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diff --git a/graphics/pgf/base/doc/pgfmanual-en-pgfkeys.tex b/graphics/pgf/base/doc/pgfmanual-en-pgfkeys.tex new file mode 100644 index 0000000000..aee930a298 --- /dev/null +++ b/graphics/pgf/base/doc/pgfmanual-en-pgfkeys.tex @@ -0,0 +1,1742 @@ +% Copyright 2019 by Till Tantau +% +% This file may be distributed and/or modified +% +% 1. under the LaTeX Project Public License and/or +% 2. under the GNU Free Documentation License. +% +% See the file doc/generic/pgf/licenses/LICENSE for more details. + + +\section{Key Management} +\label{section-keys} + +This section describes the package |pgfkeys|. It is loaded automatically by +both \pgfname\ and \tikzname. + +\begin{package}{pgfkeys} + This package can be used independently of \pgfname. Note that no + other package of \pgfname\ needs to be loaded (so neither the + emulation layer nor the system layer is needed). The Con\TeX t + abbreviation is |pgfkey| \todosp{pgfkey --> pgfkeys?} if |pgfmod| is not loaded. +\end{package} + + +\subsection{Introduction} + +\subsubsection{Comparison to Other Packages} + +The |pgfkeys| package defines a key--value management system that is in some +sense similar to the more light-weight |keyval| system and the improved +|xkeyval| system. However, |pgfkeys| uses a slightly different philosophy than +these systems and it will coexist peacefully with both of them. + +The main differences between |pgfkeys| and |xkeyval| are the following: +% +\begin{itemize} + \item |pgfkeys| organizes keys in a tree, while |keyval| and |xkeyval| + use families. In |pgfkeys| the families correspond to the root + entries of the key tree. + \item |pgfkeys| has no save-stack impact (you will have to read the \TeX + Book very carefully to appreciate this). + \item |pgfkeys| is slightly slower than |keyval|, but not much. + \item |pgfkeys| supports styles. This means that keys can just stand for + other keys (which can stand for other keys in turn or which can also + just execute some code). \tikzname\ uses this mechanism heavily. + \item |pgfkeys| supports multi-argument key code. This can, however, be + emulated in |keyval|. + \item |pgfkeys| supports handlers. These are call-backs that are called + when a key is not known. They are very flexible, in fact even + defining keys in different ways is handled by, well, handlers. +\end{itemize} + + +\subsubsection{Quick Guide to Using the Key Mechanism} + +The following quick guide to \pgfname's key mechanism only treats the most +commonly used features. For an in-depth discussion of what is going on, please +consult the remainder of this section. + +Keys are organized in a large tree that is reminiscent of the Unix file tree. A +typical key might be, say, |/tikz/coordinate system/x| or just |/x|. Again as +in Unix, when you specify keys you can provide the complete path of the key, +but you usually just provide the name of the key (corresponding to the file +name without any path) and the path is added automatically. + +Typically (but not necessarily) some code is associated with a key. To execute +this code, you use the |\pgfkeys| command. This command takes a list of +so-called key--value pairs. Each pair is of the form \meta{key}|=|\meta{value}. +For each pair the |\pgfkeys| command will execute the code stored for the +\meta{key} with its parameter set to \meta{value}. + +Here is a typical example of how the |\pgfkeys| command is used: +% +\begin{codeexample}[code only] +\pgfkeys{/my key=hallo,/your keys/main key=something\strange, + key name without path=something else} +\end{codeexample} + +Now, to set the code that is stored in a key you do not need to learn a new +command. Rather, the |\pgfkeys| command can also be used to set the code of a +key. This is done using so-called \emph{handlers}. They look like keys whose +names look like ``hidden files in Unix'' since they start with a dot. The +handler for setting the code of a key is appropriately called |/.code| and it +is used as follows: +% +\begin{codeexample}[] +\pgfkeys{/my key/.code=The value is '#1'.} +\pgfkeys{/my key=hi!} +\end{codeexample} +% +As you can see, in the first line we defined the code for the key |/my key|. In +the second line we executed this code with the parameter set to |hi!|. + +There are numerous handlers for defining a key. For instance, we can also +define a key whose value actually consists of more than one parameter. +% +\begin{codeexample}[] +\pgfkeys{/my key/.code 2 args=The values are '#1' and '#2'.} +\pgfkeys{/my key={a1}{a2}} +\end{codeexample} + +We often want to have keys where the code is called with some default value if +the user does not provide a value. Not surprisingly, this is also done using a +handler, this time called |/.default|. +% +\begin{codeexample}[] +\pgfkeys{/my key/.code=(#1)} +\pgfkeys{/my key/.default=hello} +\pgfkeys{/my key=hallo,/my key} +\end{codeexample} + +The other way round, it is also possible to specify that a value \emph{must} be +specified, using a handler called |/.value required|. Finally, you can also +require that no value \emph{may} be specified using |/.value forbidden|. + +All keys for a package like, say, \tikzname\ start with the path |/tikz|. We +obviously do not like to write this path down every time we use a key (so we do +not have to write things like |\draw[/tikz/line width=1cm]|). What we need is +to somehow ``change the default path to a specific location''. This is done +using the handler |/.cd| (for ``change directory''). Once this handler has been +used on a key, all subsequent keys {\itshape in the current call of |\pgfkeys| +only} are automatically prefixed with this path, if necessary. + +Here is an example: +% +\begin{codeexample}[code only] +\pgfkeys{/tikz/.cd,line width=1cm,line cap=round} +\end{codeexample} +% +This makes it easy to define commands like |\tikzset|, which could be defined +as follows (the actual definition is a bit faster, but the effect is the same): +% +\begin{codeexample}[code only] +\def\tikzset#1{\pgfkeys{/tikz/.cd,#1}} +\end{codeexample} + +When a key is handled, instead of executing some code, the key can also cause +further keys to be executed. Such keys will be called \emph{styles}. A style +is, in essence, just a key list that should be executed whenever the style is +executed. Here is an example: +% +\begin{codeexample}[] +\pgfkeys{/a/.code=(a:#1)} +\pgfkeys{/b/.code=(b:#1)} +\pgfkeys{/my style/.style={/a=foo,/b=bar,/a=#1}} +\pgfkeys{/my style=wow} +\end{codeexample} +% +As the above example shows, styles can also be parameterized, just like the +normal code keys. + +As a typical use of styles, suppose we wish to set up the key |/tikz| so that +it will change the default path to |/tikz|. This can be achieved as follows: +% +\begin{codeexample}[code only] +\pgfkeys{/tikz/.style=/tikz/.cd} +\pgfkeys{tikz,line width=1cm,draw=red} +\end{codeexample} + +Note that when |\pgfkeys| is executed, the default path is set to~|/|. This +means that the first |tikz| will be completed to |/tikz|. Then |/tikz| is a +style and, thus, replaced by |/tikz/.cd|, which changes the default path to +|/tikz|. Thus, the |line width| is correctly prefixed with |/tikz|. + + +\subsection{The Key Tree} + +The |pgfkeys| package organizes keys in a so-called \emph{key tree}. This tree +will be familiar to anyone who has used a Unix operating system: A key is +addressed by a path, which consists of different parts separated by slashes. A +typical key might be |/tikz/line width| or just |/tikz| or something more +complicated like |/tikz/cs/x/.store in|. + +Let us fix some further terminology: Given a key like |/a/b/c|, we call the +part leading up the last slash (|/a/b|) the \emph{path} of the key. We call +everything after the last slash (|c|) the \emph{name} of the key (in a file +system this would be the file name). + +We do not always wish to specify keys completely. Instead, we usually specify +only part of a key (typically only the name) and the \emph{default path} is +then added to the key at the front. So, when the default path is |/tikz| and +you refer to the (partial) key |line width|, the actual key that is used is +|/tikz/line width|. There is a simple rule for deciding whether a key is a +partial key or a full key: If it starts with a slash, then it is a full key and +it is not modified; if it does not start with a slash, then the default path is +automatically prefixed. + +\emph{Remark:} The above rule is actually a definition, hence the corresponding +sufficiency conditions hold. That is, if it is a full key, then it starts with +a slash; if it is a partial key, then it does not start with a slash. Moreover, +a path always starts with a slash. + +Note that the default path is not the same as a search path. In particular, the +default path is just a single path. When a partial key is given, only this +single default path is prefixed; |pgfkeys| does not try to look up the key in +different parts of a search path. It is, however, possible to emulate search +paths, but a much more complicated mechanism must be used. + +When you set keys (to be explained in a moment), you can freely mix partial and +full keys and you can change the default path. This makes it possible to +temporarily use keys from another part of the key tree (this turns out to be a +very useful feature). + +Each key (may) store some \emph{tokens} and there exist commands, described +below, for setting, getting, and changing the tokens stored in a key. However, +you will only very seldom use these commands directly. Rather, the standard way +of using keys is the |\pgfkeys| command or some command that uses it internally +like, say, |\tikzset|. So, you may wish to skip the following commands and +continue with the next subsection. + +\begin{command}{\pgfkeyssetvalue\marg{full key}\marg{token text}} + Stores the \meta{token text} in the \meta{full key}. The \meta{full key} + may not be a partial key, so no default-path-adding is done. The + \meta{token text} can be arbitrary tokens and may even contain things like + |#| or unbalanced \TeX-ifs. + % +\begin{codeexample}[] +\pgfkeyssetvalue{/my family/my key}{Hello, world!} +\pgfkeysvalueof{/my family/my key} +\end{codeexample} + + The setting of a key is always local to the current \TeX\ group. +\end{command} + +\begin{command}{\pgfkeyssetevalue\marg{full key}\marg{token text}} + The |\edef| version of |\pgfkeyssetvalue|. +\end{command} + +\begin{command}{\pgfkeyslet\marg{full key}\marg{macro}} + Performs a |\let| statement so the \meta{full key} points to the contents + of \meta{macro}. + % +\begin{codeexample}[] +\def\helloworld{Hello, world!} +\pgfkeyslet{/my family/my key}{\helloworld} +\pgfkeysvalueof{/my family/my key} +\end{codeexample} + % + You should never let a key be equal to |\relax|. Such a key may or may not + be indistinguishable from an undefined key. +\end{command} + +\begin{command}{\pgfkeysgetvalue\marg{full key}\marg{macro}} + Retrieves the tokens stored in the \meta{full key} and lets \meta{macro} be + equal to these tokens. If the key has not been set, the \meta{macro} will + be equal to |\relax|. + % +\begin{codeexample}[] +\pgfkeyssetvalue{/my family/my key}{Hello, world!} +\pgfkeysgetvalue{/my family/my key}{\helloworld} +\helloworld +\end{codeexample} + % +\end{command} + +\begin{command}{\pgfkeysvalueof\marg{full key}} + Inserts the value stored in \meta{full key} at the current position into the + text. It expands to an alias of the primitive |\relax| if the key is undefined. + % +\begin{codeexample}[] +\pgfkeyssetvalue{/my family/my key}{Hello, world!} +\pgfkeysvalueof{/my family/my key} +\end{codeexample} + % + \emph{Note:} It is an error to assign to the result of the expansion of + |\pgfkeysvalueof|, not only semantically but in recent versions of \pgfname\ + also logically. To set the value of a key \emph{always} use the appropriate + interfaces, e.g.\ |\pgfkeyssetvalue|. +\end{command} + +\begin{command}{\pgfkeysifdefined\marg{full key}\marg{if}\marg{else}} + Checks whether this key was previously set using either |\pgfkeyssetvalue| + or |\pgfkeyslet|. If so, the code in \meta{if} is executed, otherwise the + code in \meta{else}. + % +\begin{codeexample}[] +\pgfkeyssetvalue{/my family/my key}{Hello, world!} +\pgfkeysifdefined{/my family/my key}{yes}{no} +\end{codeexample} + % +\end{command} + + +\subsection{Setting Keys} + +Setting keys is done using a powerful command called |\pgfkeys|. This command +takes a list of so-called \emph{key--value pairs}. These are pairs of the form +\meta{key}|=|\meta{value}. The principal idea is the following: For each pair +in the list, some \emph{action} is taken. This action can be one of the +following: +% +\begin{enumerate} + \item A command is executed whose argument(s) are \meta{value}. This + command is stored in a special subkey of \meta{key}. + \item The \meta{value} is stored in the \meta{key} itself. + \item If the key's name (the part after the last slash) is a known + \emph{handler}, then this handler will take care of the key. + \item If the key is totally unknown, one of several possible \emph{unknown + key handlers} is called. +\end{enumerate} + +Additionally, if the \meta{value} is missing, a default value may or may not be +substituted. Before we plunge into all the details, let us have a quick look at +the command itself. + +\begin{command}{\pgfkeys\marg{key list}} + The \meta{key list} should be a list of key--value pairs, separated by + commas. A key--value pair can have the following two forms: + \meta{key}|=|\meta{value} or just \meta{key}. Any spaces around the + \meta{key} or around the \meta{value} are removed. It is permissible to + surround both the \meta{key} or the \meta{value} in curly braces, which are + also removed. Especially putting the \meta{value} in curly braces needs to + be done quite often, namely whenever the \meta{value} contains an + equal-sign or a comma. + + The key--value pairs in the list are handled in the order they appear. How + this handling is done, exactly, is described in the rest of this section. + + If a \meta{key} is a partial key, the current value of the default path is + prefixed to the \meta{key} and this ``upgraded'' key is then used. The + default path is just the root path |/| when the first key is handled, but + it may change later on. At the end of the command, the default path is + reset to the value it had before this command was executed. + + Calls of this command may be nested. Thus, it is permissible to call + |\pgfkeys| inside the code that is executed for a key. Since the default + path is restored after a call of |\pgfkeys|, the default path will not + change when you call |\pgfkeys| while executing code for a key (which is + exactly what you want). +\end{command} + +\begin{command}{\pgfqkeys\marg{default path}\marg{key list}} + This command has the same effect as |\pgfkeys{|\meta{default + path}|/.cd,|\meta{key list}|}|, it is only marginally quicker. This command + should not be used in user code, but rather in commands like |\tikzset| or + |\pgfset| that get called very often. +\end{command} + +\begin{command}{\pgfkeysalso\marg{key list}} + This command has exactly the same effect as |\pgfkeys|, only the default + path is not modified before or after the keys are being set. This command + is mainly intended to be called by the code that is being processed for a + key. +\end{command} + +\begin{command}{\pgfqkeysalso\marg{default path}\marg{key list}} + This command has the same effect as |\pgfkeysalso{|\meta{default + path}|/.cd,|\meta{key list}|}|, it is only quicker. Changing the default + path inside a |\pgfkeyalso| is dangerous, so use with care. A rather safe + place to call this command is at the beginning of a \TeX\ group. +\end{command} + + +\subsubsection{First Char Syntax Detection} +\label{sec:pgf:first:char:syntax} + +Usually, keys are of the form \meta{key}|=|\meta{value} and how such keys are +handled is discussed in the rest of this section. However, it is also possible +to setup a different syntax for certain parts of the input to |\pgfkeys|. Since +this is a rather advanced option, most readers may wish to skip the following +discussion upon first reading; it is discussed here because this special syntax +detection is the very first thing that is done when a key is processed, before +any of the following operations are performed. + +The |\pgfkeys| command and its variants decompose their input into a list of +\meta{string}s that are separated by commas. By default, each such +\meta{string} must either have the form \meta{key}|=|\meta{value} or of the +form \meta{key} with the value-part missing. However, you might wish to +interpret some of these strings differently. For instance, when a \meta{string} +has the form |"|\meta{text}|"|, you might wish the \meta{string} to be +interpreted as if one had written |label text={|\meta{text}|}|. Then, people +could write +% +\begin{codeexample}[code only] +\myset{red, "main valve", thick} +\end{codeexample} +% +instead of the more cumbersome +% +\begin{codeexample}[code only] +\myset{red, label text=main valve, thick} +\end{codeexample} +% +An example where such a syntax reinterpretation is done is the |quotes| +library, which allows you to write things like +% +\begin{codeexample}[preamble={\usetikzlibrary{graphs,quotes}}] +\tikz \graph { a ->["1" red] b ->["0"] c }; +\end{codeexample} +% +\noindent instead of the somewhat longer +% +\begin{codeexample}[preamble={\usetikzlibrary{graphs}}] +\tikz \graph { a ->[edge node={node[red,auto]{1}}] b ->[edge label=0] c }; +\end{codeexample} + +In order to detect whether a \meta{string} has a special syntax, you can +request that the \emph{first character} of \meta{string} is analysed by the key +parser. If this first character matches a character that has been flagged as a +special character, the \meta{string} is not interpreted as a usual key--value +pair. Instead, \meta{string} is passed as a parameter to a special macro that +should take care of the \meta{string}. After this macro has finished, the +parsing continues with the \meta{next string} in the list. + +In order to setup a special syntax handling for \meta{strings} that begin with +a certain character, two things need to be done: +% +\begin{enumerate} + \item First, the whole |first char syntax| detection must be ``switched on'', + since, by default, it is turned off for efficiency reasons (the + overhead is rather small, however). This is done by setting the + following key: + % + \begin{key}{/handlers/first char syntax=\opt{\meta{true or false}} (default true, initially false)} + \end{key} + \item Second, in order to handle strings starting with a certain + \meta{character} in a special way, you need to store a macro in the + following key: + % + \begin{key}{/handlers/first char syntax/\meta{meaning of character}} + The \meta{meaning of character} should be the text that \TeX's + command |\meaning| returns for a macro that has been |\let| to the + \meta{character}. For instance, when strings starting with |"| + should be treated in a special way, the \meta{meaning of character} + would be the string |the character "| since this is what \TeX\ + writes when you say + % +\begin{codeexample}[] +\let\mycharacter=" +\meaning\mycharacter +\end{codeexample} + % + Now, the key |/handlers/first char syntax/|\meta{meaning of + character} should be setup (using |\pgfkeyssetvalue| or using the + |.initial| handler) to store a \meta{macro name}. + + If this is the case and if \meta{string} starts with the + \meta{character} (blanks at the beginning of \meta{string} are + deleted prior to this test), then \meta{macro name} is called with + \meta{string} as its argument. + \end{key} +\end{enumerate} + +Let us now have a look at an example. We install two handlers, one for strings +starting with |"| and one for strings starting with |<|. +% +\begin{codeexample}[] +\pgfkeys{ + /handlers/first char syntax=true, + /handlers/first char syntax/the character "/.initial=\myquotemacro, + /handlers/first char syntax/the character </.initial=\mypointedmacro, +} + +\def\myquotemacro#1{Quoted: #1. } +\def\mypointedmacro#1{Pointed: #1. } + +\ttfamily \pgfkeys{"foo", <bar>} +\end{codeexample} + +Naturally, in the above examples, the two handling macros did not do something +particularly exciting. In the next example, we setup a more elaborate macro +that mimics a small part the behavior of the |quotes| library, only for single +quotes: +% +\begin{codeexample}[] +\pgfkeys{ + /handlers/first char syntax=true, + /handlers/first char syntax/the character '/.initial=\mysinglequotemacro +} + +\def\mysinglequotemacro#1{\pgfkeysalso{label={#1}}} + +\tikz \node [circle, 'foo', draw] {bar}; +\end{codeexample} + +Note that in the above example, the macro |\mysinglequotemacro| gets passed the +complete string, including the single quotes. It is the job of the macro to get +rid of them, if this is necessary. + +The first char syntax detection allows you to perform rather powerful +transformations on the syntax of keys -- provided you can ``pin down'' the +syntax on the first character. In the following example, you can write +expressions in parentheses in front of a key--value pair and the pair will only +be executed when the expression evaluates to true: +% +\begin{codeexample}[] +\pgfkeys{ + /handlers/first char syntax=true, + /handlers/first char syntax/the character (/.initial=\myparamacro +} + +\def\myparamacro#1{\myparaparser#1\someendtext} +\def\myparaparser(#1)#2\someendtext{ + \pgfmathparse{#1} + \ifx\pgfmathresult\onetext + \pgfkeysalso{#2} + \fi +} +\def\onetext{1} + +\foreach \i in {1,...,4} + \tikz \node [draw, thick, rectangle, (pi>\i) circle, (pi>\i*2) draw=red] {x}; +\end{codeexample} + + +\subsubsection{Default Arguments} + +The arguments of the |\pgfkeys| command can either be of the form +\meta{key}|=|\meta{value} or of the form \meta{key} with the value-part +missing. In the second case, the |\pgfkeys| will try to provide a \emph{default +value} for the \meta{value}. If such a default value is defined, it will be +used as if you had written \meta{key}|=|\meta{default value}. + +In the following, the details of how default values are determined is +described; however, you should normally use the handlers |/.default| and +|/.value required| as described in Section~\ref{section-default-handlers} and +you may wish to skip the following details. + +When |\pgfkeys| encounters a \meta{key} without an equal-sign, the following +happens: +% +\begin{enumerate} + \item The input is replaced by \meta{key}|=\pgfkeysnovalue|. In particular, + the commands |\pgfkeys{my key}| and + % FIXME: there is a bug in the pretty printer ... fix it and get rid of '||' here: + |\pgfkeys{my key=||\pgfkeysnovalue}| have exactly the same effect and + you can ``simulate'' a missing value by providing the value + |\pgfkeysnovalue|, which is sometimes useful. + \item If the \meta{value} is |\pgfkeysnovalue|, then it is checked whether + the subkey \meta{key}|/.@def| exists. For instance, if you write + |\pgfkeys{/my key}|, then it is checked whether the key |/my key/.@def| + exists. + \item If the key \meta{key}|/.@def| exists, then the tokens stored in this + key are used as \meta{value}. + \item If the key does not exist, then |\pgfkeysnovalue| is used as the + \meta{value}. + \item At the end, if the \meta{value} is now equal to + |\pgfkeysvaluerequired|, then the code (or something fairly equivalent) + |\pgfkeys{/errors/value required=|\meta{key}|{}}| is executed. Thus, by + changing this key you can change the error message that is printed or + you can handle the missing value in some other way. +\end{enumerate} + + +\subsubsection{Keys That Execute Commands} +\label{section-key-code} + +After the transformation process described in the previous subsection, we +arrive at a key of the form \meta{key}=\meta{value}, where \meta{key} is a full +key. Different things can now happen, but always the macro |\pgfkeyscurrentkey| +will have been set up to expand to the text of the \meta{key} that is currently +being processed. + +The first things that is tested is whether the key \meta{key}|/.@cmd| exists. +If this is the case, then it is assumed that this key stores the code of a +macro and this macro is executed. The argument of this macro is \meta{value} +directly followed by |\pgfeov|, which stands for ``end of value''. The +\meta{value} is not surrounded by braces. After this code has been executed, +|\pgfkeys| continues with the next key in the \meta{key list}. + +It may seem quite peculiar that the macro stored in the key \meta{key}|/.@cmd| +is not simply executed with the argument |{|\meta{value}|}|. However, the +approach taken in the |pgfkeys| packages allows for more flexibility. For +instance, assume that you have a key that expects a \meta{value} of the form +``\meta{text}|+|\meta{more text}'' and wishes to store \meta{text} and +\meta{more text} in two different macros. This can be achieved as follows: +% +\begin{codeexample}[] +\def\mystore#1+#2\pgfeov{\def\a{#1}\def\b{#2}} +\pgfkeyslet{/my key/.@cmd}{\mystore} +\pgfkeys{/my key=hello+world} + +|\a| is \a, |\b| is \b. +\end{codeexample} + +Naturally, defining the code to be stored in a key in the above manner is too +awkward. The following commands simplify things a bit, but the usual manner of +setting up code for a key is to use one of the handlers described in +Section~\ref{section-code-handlers}. + +\begin{command}{\pgfkeysdef\marg{key}\marg{code}} + This command temporarily defines a \TeX-macro with the argument list + |#1\pgfeov| and then lets \meta{key}|/.@cmd| be equal to this macro. The + net effect of all this is that you have then set up code for the key + \meta{key} so that when you write |\pgfkeys{|\meta{key}|=|\meta{value}|}|, + then the \meta{code} is executed with all occurrences of |#1| in + \meta{code} being replaced by \meta{value}. (This behavior is quite + similar to the |\define@key| command of |keyval| and |xkeyval|). + % +\begin{codeexample}[] +\pgfkeysdef{/my key}{#1, #1.} +\pgfkeys{/my key=hello} +\end{codeexample} +\end{command} + +\begin{command}{\pgfkeysedef\marg{key}\marg{code}} + This command works like |\pgfkeysdef|, but it uses |\edef| rather than + |\def| when defining the key macro. If you do not know the difference + between the two, then you will not need this command; and if you know the + difference, then you will know when you need this command. +\end{command} + +\begin{command}{\pgfkeysdefnargs\marg{key}\marg{argument count}\marg{code}} + This command works like |\pgfkeysdef|, but it allows you to provide an + arbitrary \meta{argument count} between $0$ and $9$ (inclusive). + % +\begin{codeexample}[] +\pgfkeysdefnargs{/my key}{2}{\def\a{#1}\def\b{#2}} +\pgfkeys{/my key= + {hello} + {world}} + +|\a| is `\a', |\b| is `\b'. +\end{codeexample} + % + The resulting key will expect exactly \marg{argument count} arguments. +\end{command} +% +\begin{command}{\pgfkeysedefnargs\marg{key}\marg{argument count}\marg{code}} + The |\edef| version of |\pgfkeysdefnargs|. +\end{command} + +\begin{command}{\pgfkeysdefargs\marg{key}\marg{argument pattern}\marg{code}} + This command works like |\pgfkeysdefnargs|, but it allows you to provide an + arbitrary \meta{argument pattern} rather than just a number of arguments. + % +\begin{codeexample}[] +\pgfkeysdefargs{/my key}{#1+#2}{\def\a{#1}\def\b{#2}} +\pgfkeys{/my key=hello+world} + +|\a| is \a, |\b| is \b. +\end{codeexample} + % + Note that |\pgfkeysdefnargs| is \emph{better} when it comes to simple + argument \emph{counts}\footnote{When the resulting keys are used, the + \texttt{defnargs} variant allows spaces between arguments whereas the + \texttt{defargs} variant does not; it considers the spaces as part of the + argument.}. +\end{command} + +\begin{command}{\pgfkeysedefargs\marg{key}\marg{argument pattern}\marg{code}} + The |\edef| version of |\pgfkeysdefargs|. +\end{command} + + +\subsubsection{Keys That Store Values} + +Let us continue with what happens when |\pgfkeys| processes the current key and +the subkey \meta{key}|/.@cmd| is not defined. Then it is checked whether the +\meta{key} itself exists (has been previously assigned a value using, for +instance, |\pgfkeyssetvalue|). In this case, the tokens stored in \meta{key} +are replaced by \meta{value} and |\pgfkeys| proceeds with the next key in the +\meta{key list}. + + +\subsubsection{Keys That Are Handled} +\label{section-key-handlers} + +If neither the \meta{key} itself nor the subkey \meta{key}|/.@cmd| are defined, +then the \meta{key} cannot be processed ``all by itself''. Rather, a +\meta{handler} is needed for this key. Most of the power of |pgfkeys| comes +from the proper use of such handlers. + +Recall that the \meta{key} is always a full key (if it was not originally, it +has already been upgraded at this point to a full key). It decomposed into two +parts: + +\begin{enumerate} + \item The \meta{path} of \meta{key} (everything before the last slash) is + stored in the macro |\pgfkeyscurrentpath|. + \item The \meta{name} of \meta{key} (everything after the last slash) is + stored in the macro |\pgfkeyscurrentname|. + + It is recommended (but not necessary) that the name of a handler starts + with a dot (but not with |.@|), so that they are easy to detect for the + reader. +\end{enumerate} + +(For efficiency reasons, these two macros are only set up at this point; so +when code is executed for a key in the ``usual'' manner then these macros are +not set up.) + +The |\pgfkeys| command now checks whether the key +|/handlers/|\meta{name}|/.@cmd| exists. If so, it should store a command and +this command is executed exactly in the same manner as described in +Section~\ref{section-key-code}. Thus, this code gets the \meta{value} that was +originally intended for \meta{key} as its argument, followed by |\pgfeov|. It +is the job of the handlers to do something useful with the \meta{value}. + +For an example, let us write a handler that will output the value stored in a +key to the log file. We call this handler |/.print to log|. The idea is that +when someone tries to use the key |/my key/.print to log|, then this key will +not be defined and the handler gets executed. The handler will then have access +to the path-part of the key, which is |/my key|, via the macro +|\pgfkeyscurrentpath|. It can then lookup which value is stored in this key and +print it. +% +\begin{codeexample}[code only] +\pgfkeysdef{/handlers/.print to log} +{% + \pgfkeysgetvalue{\pgfkeyscurrentpath}{\temp} + \writetolog{\temp} +} +\pgfkeyssetvalue{/my key}{Hi!} +... +\pgfkeys{/my key/.print to log} +\end{codeexample} +% +The above code will print |Hi!| in the log, provided the macro |\writetolog| is +set up appropriately. + +For a more interesting handler, let us program a handler that will set up a key +so that when the key is used, some code is executed. This code is given as +\meta{value}. All the handler must do is to call |\pgfkeysdef| for the path of +the key (which misses the handler's name) and assign the parameter value to it. +% +\begin{codeexample}[] +\pgfkeysdef{/handlers/.my code}{\pgfkeysdef{\pgfkeyscurrentpath}{#1}} +\pgfkeys{/my key/.my code=(#1)} +\pgfkeys{/my key=hallo} +\end{codeexample} + +There are some parameters for handled keys which prove to be useful in some +(possibly rare) special cases: +% +\begin{key}{/handler config=\mchoice{all,only existing,full or existing} (initially all)} + Changes the initial configuration how key handlers will be used. + + This configuration is for advanced users and rarely necessary. + % + \begin{description} + \item[\texttt{all}] The preconfigured setting |all| works as described + above and imposes no restriction on the key setting process. + \item[\texttt{only existing}] The value |only existing| modifies the + algorithm for handled keys as follows: a handler \meta{key + name}|/.|\meta{handler} will be executed only if \meta{key name} is + either a key which stores its value directly or a command key for + which |/.@cmd| exists. If \meta{key name} does \emph{not} exist + already, the complete string \meta{key name}|/.|\meta{handler} is + considered to be an unknown key and the procedure described in the + next section applies (for the path of \meta{key name}). + % +\begin{codeexample}[] +% Define a test key and error handlers: +\pgfkeys{/the/key/.code={Initial definition. }} +\pgfkeys{/handlers/.unknown/.code={Unknown key `\pgfkeyscurrentkey'. }} + +% calling the test key yields 'Initial definition. ': +\pgfkeys{/the/key} + +% Change configuration: +\pgfkeys{/handler config=only existing} + +% allowed: key *re*-definition: +\pgfkeys{/the/key/.code={Re-Definition. }} +% calling the key yields 'Re-Definition. ': +\pgfkeys{/the/key} + +% not allowed: definition of new keys: +% this checks for '/the/other key/.unknown' +% and '/handlers/.unknown' +% and yields finally +% 'Unknown key `/the/other key/.code`' +\pgfkeys{/the/other key/.code={New definition. }} +\end{codeexample} + % + It is necessary to exclude some key handlers from this procedure. + Altogether, the detailed procedure is as follows: + % + \begin{enumerate} + \item If a handled key like |/a path/a key/.a handler=value| is + encountered, it is checked whether the handler should be + invoked. This is the case if + % + \begin{itemize} + \item An exception from |only existing| for this key + exists (see below), + \item The key |/a path/a key| exists already -- either + directly as storage key or with the |.@cmd| suffix. + \end{itemize} + % + \item If the check passes, everything works as before. + \item If the check fails, the complete key will be considered + to be unknown. In that case, the handling of unknown keys + as described in the next section applies. There, the + current key path will be set to |/a path| and the current + key's name to |key/.a handler|. + \end{enumerate} + + A consequence of this configuration is to provide more meaningful + processing of handled keys if a search path for keys is in effect, + see section~\ref{sec:pgf:unknown:keys} for an example. + \item[\texttt{full or existing}] Finally, the choice |full or existing| + is a variant of |only existing|: it works in the same way for keys + which do not have a full key path. For example, the style + + |\pgfkeys{/my path/.cd,key/.style={|$\dotsc$|}}| + + can only be redefined: it doesn't have a full path, so the + |only existing| mechanism applies. But the style + + |\pgfkeys{/my path/key/.style={|$\dotsc$|}}| + + will still work. This allows users to override the |only existing| + feature if they know what they're doing (and provide full key + paths). + \end{description} +\end{key} + +\begin{key}{/handler config/only existing/add exception=\marg{key handler name}} + Allows to add exceptions to the |/handler config=only existing| feature. + Initially exceptions for the key handlers |/.cd|, |/.try|, |/.retry|, + |/.lastretry| and |/.unknown| are defined. The value \marg{key handler + name} should be the name of a key handler. +\end{key} + + +\subsubsection{Keys That Are Unknown} +\label{sec:pgf:unknown:keys} + +For some keys, neither the key, nor its |.@cmd| subkey nor a handler is +defined. In this case, it is checked whether the key \meta{current +path}|/.unknown/.@cmd| exists. Thus, when you try to use the key +|/tikz/strange|, then it is checked whether |/tikz/.unknown/.@cmd| exists. If +this key exists (which it does), it is executed. This code can then try to make +sense of the key. For instance, the handler for \tikzname\ will try to +interpret the key's name as a color or as an arrow specification or as a +\pgfname\ option. + +You can set up unknown key handlers for your own keys by simply setting the +code of the key \meta{my path prefix}|/.unknown|. This also allows you to set +up ``search paths''. The idea is that you would like keys to be searched not +only in a single default path, but in several. Suppose, for instance, that you +would like keys to be searched for in |/a|, |/b|, and |/b/c|. We set up a key +|/my search path| for this: +% +\begin{codeexample}[code only] +\pgfkeys{/my search path/.unknown/.code= + {% + \let\searchname=\pgfkeyscurrentname% + \pgfkeysalso{% + /a/\searchname/.try=#1, + /b/\searchname/.retry=#1, + /b/c/\searchname/.retry=#1% + }% + }% +} +\pgfkeys{/my search path/.cd,foo,bar} +\end{codeexample} +% +In the above code, |foo| and |bar| will be searched for in the three +directories |/a|, |/b|, and |/b/c|. Before you start implementing search paths +using this pattern, consider the |/.search also| handler discussed below. + +If the key \meta{current path}|/.unknown/.@cmd| does not exist, the handler +|/handlers/.unknown| is invoked instead, which is always defined and which +prints an error message by default. + + +\subsubsection{Search Paths And Handled Keys} + +There is one special case which occurs in the search path example above. What +happens if we want to change a style? For example, +% +\begin{codeexample}[code only] +\pgfkeys{/my search path/.cd,custom/.style={variables}} +\end{codeexample} +% +\noindent could mean a style in |/my search path/|, |/a/|, |/b/| or even +|/b/c/|! + +Due to the rules for handled keys, the answer is +|/my search path/custom/.style={variables}|. It may be useful to modify this +default behavior. One useful thing would be to search for \emph{existing} +styles named |custom| and redefine them. For example, if a style |/b/custom| +exists, the assignment |custom/.style={variables}| should probably redefine +|/b/custom| instead of |/my search path/custom|. This can be done using +|handler config|: +% +\begin{codeexample}[] +\pgfkeys{/my search path/.unknown/.code= + {% + \let\searchname=\pgfkeyscurrentname% + \pgfkeysalso{% + /a/\searchname/.try=#1, + /b/\searchname/.retry=#1, + /b/c/\searchname/.retry=#1% + }% + }% +} + +% Let's define /b/custom here: +\pgfkeys{/b/custom/.code={This is `\pgfkeyscurrentkey'. }} + +% Reconfigure treatment of key handlers: +\pgfkeys{/handler config=only existing} + +% The search path procedure will find /b/custom +% -> leads to This is `/b/custom' +\pgfkeys{/my search path/.cd,custom} + +% Due to the reconfiguration, this will find /b/custom instead of +% defining /my search path/custom: +\pgfkeys{/my search path/.cd,custom/.append code={Modified. }} + +% So using the search path, we again find /b/custom which +% leads to This is `/b/custom' Modified +\pgfkeys{/my search path/.cd,custom} +\end{codeexample} + +A slightly different approach to search paths can be realized using the +|/.search also| key handler, see below. + + +\subsection{Key Handlers} + +We now describe which key handlers are defined by default. You can also define +new ones as described in Section~\ref{section-key-handlers}. + + +\subsubsection{Handlers for Path Management} + +\begin{handler}{{.cd}} + This handler causes the default path to be set to \meta{key}. Note that the + default path is reset at the beginning of each call to |\pgfkeys| to be + equal to~|/|. + + \example |\pgfkeys{/tikz/.cd,...}| +\end{handler} + +\begin{handler}{{.is family}} +\label{section-is family-handler} + This handler sets up things such that when \meta{key} is executed, then the + current path is set to \meta{key}. A typical use is the following: + % +\begin{codeexample}[code only] +\pgfkeys{/tikz/.is family} +\pgfkeys{tikz,line width=1cm} +\end{codeexample} + % + The effect of this handler is the same as if you had written + \meta{key}|/.style=|\meta{key}|/.cd|, only the code produced by the + |/.is family| handler is quicker. +\end{handler} + + +\subsubsection{Setting Defaults} +\label{section-default-handlers} + +\begin{handler}{{.default}|=|\meta{value}} + Sets the default value of \meta{key} to \meta{value}. This means that + whenever no value is provided in a call to |\pgfkeys|, then this + \meta{value} will be used instead. + + \example |\pgfkeys{/width/.default=1cm}| +\end{handler} + +\begin{handler}{{.value required}} + This handler causes the error message key |/errors/value required| to be + issued whenever the \meta{key} is used without a value. + + \example |\pgfkeys{/width/.value required}| +\end{handler} + +\begin{handler}{{.value forbidden}} + This handler causes the error message key |/errors/value forbidden| to be + issued whenever the \meta{key} is used with a value. + + This handler works be adding code to the code of the key. This means that + you have to define the key first before you can use this handler. + % +\begin{codeexample}[code only] +\pgfkeys{/my key/.code=I do not want an argument!} +\pgfkeys{/my key/.value forbidden} + +\pgfkeys{/my key} % Ok +\pgfkeys{/my key=foo} % Error +\end{codeexample} + % +\end{handler} + + +\subsubsection{Defining Key Codes} +\label{section-code-handlers} + +A number of handlers exist for defining the code of keys. + +\begin{handler}{{.code}|=|\meta{code}} + This handler executes |\pgfkeysdef| with the parameters \meta{key} and + \meta{code}. This means that, afterwards, whenever the \meta{key} is used, + the \meta{code} gets executed. More precisely, when + \meta{key}|=|\meta{value} is encountered in a key list, \meta{code} is + executed with any occurrence of |#1| replaced by \meta{value}. As always, + if no \meta{value} is given, the default value is used, if defined, or the + special value |\pgfkeysnovalue|. + + It is permissible that \meta{code} calls the command |\pgfkeys|. It is also + permissible the \meta{code} calls the command |\pgfkeysalso|, which is + useful for styles, see below. + % +\begin{codeexample}[code only] +\pgfkeys{/par indent/.code={\parindent=#1},/par indent/.default=2em} +\pgfkeys{/par indent=1cm} +... +\pgfkeys{/par indent} +\end{codeexample} + % +\end{handler} + +\begin{handler}{{.ecode}|=|\meta{code}} + This handler works like |/.code|, only the command |\pgfkeysedef| is used. +\end{handler} + +\begin{handler}{{.code 2 args}|=|\meta{code}} + This handler works like |/.code|, only two arguments rather than one are + expected when the \meta{code} is executed. This means that when + \meta{key}|=|\meta{value} is encountered in a key list, the \meta{value} + should consist of two arguments. For instance, \meta{value} could be + |{first}{second}|. Then \meta{code} is executed with any occurrence of |#1| + replaced |first| and any occurrence of |#2| replaced by |second|. + % +\begin{codeexample}[code only] +\pgfkeys{/page size/.code 2 args={\paperheight=#2\paperwidth=#1}} +\pgfkeys{/page size={30cm}{20cm}} +\end{codeexample} + % + Because of the special way the \meta{value} is parsed, if you set + \meta{value} to, for instance, |first| (without any braces), then |#1| will + be set to |f| and |#2| will be set to |irst|. +\end{handler} + +\begin{handler}{{.ecode 2 args}|=|\meta{code}} + This handler works like |/.code 2 args|, only an |\edef| is used rather + than a |\def| to define the macro. +\end{handler} + +\begin{handler}{{.code n args}|=|\marg{argument count}\marg{code}} + This handler also works like |/.code|, but you can now specify a number of + arguments between $0$ and $9$ (inclusive). + % +\begin{codeexample}[] +\pgfkeys{/a key/.code n args={2}{First=`#1', Second=`#2'}} +\pgfkeys{/a key={A}{B}} +\end{codeexample} + % + In contrast to |/.code 2 args|, there must be exactly \meta{argument count} + arguments, not more and not less and these arguments should be properly + delimited. +\end{handler} + +\begin{handler}{{.ecode n args}|=|\marg{argument count}\marg{code}} + This handler works like |/.code n args|, only an |\edef| is used rather + than a |\def| to define the macro. +\end{handler} + +\begin{handler}{{.code args}|=|\marg{argument pattern}\marg{code}} + This handler is the most flexible way to define a |/.code| key: you can now + specify an arbitrary \meta{argument pattern}. Such a pattern is a usual + \TeX\ macro pattern. For instance, suppose \meta{argument pattern} is + |(#1/#2)| and \meta{key}|=|\meta{value} is encountered in a key list with + \meta{value} being |(first/second)|. Then \meta{code} is executed with any + occurrence of |#1| replaced |first| and any occurrence of |#2| replaced by + |second|. So, the actual \meta{value} is matched against the \meta{argument + pattern} in the standard \TeX\ way. + % +\begin{codeexample}[code only] +\pgfkeys{/page size/.code args={#1 and #2}{\paperheight=#2\paperwidth=#1}} +\pgfkeys{/page size=30cm and 20cm} +\end{codeexample} + + Note that |/.code n args| should be preferred in case you need just a + number of arguments (when the resulting keys are used, |/.code n args| + gobbles spaces between the arguments whereas |/.code args| considers spaces + to be part of the argument). +\end{handler} + +\begin{handler}{{.ecode args}|=|\marg{argument pattern}\marg{code}} + This handler works like |/.code args|, only an |\edef| is used rather than + a |\def| to define the macro. +\end{handler} + +There are also handlers for modifying existing keys. + +\begin{handler}{{.add code}|=|\marg{prefix code}\marg{append code}} + This handler adds code to an existing key. The \meta{prefix code} is added + to the code stored in \meta{key}|/.@cmd| at the beginning, the \meta{append + code} is added to this code at the end. Either can be empty. The argument + list of \meta{code} cannot be changed using this handler. Note that both + \meta{prefix code} and \meta{append code} may contain parameters like |#2|. + % +\begin{codeexample}[code only] +\pgfkeys{/par indent/.code={\parindent=#1}} +\newdimen\myparindent +\pgfkeys{/par indent/.add code={}{\myparindent=#1}} +... +\pgfkeys{/par indent=1cm} % This will set both \parindent and + % \myparindent to 1cm +\end{codeexample} + % +\end{handler} + +\begin{handler}{{.prefix code}|=|\meta{prefix code}} + This handler is a shortcut for \meta{key}|/.add code={|\meta{prefix + code}|}{}|. That is, this handler adds the \meta{prefix code} at the + beginning of the code stored in \meta{key}|/.@cmd|. +\end{handler} + +\begin{handler}{{.append code}|=|\meta{append code}} + This handler is a shortcut for \meta{key}|/.add code={}{|\meta{append + code}|}|. +\end{handler} + + +\subsubsection{Defining Styles} + +The following handlers allow you to define \emph{styles}. A style is a key list +that is processed whenever the style is given as a key in a key list. Thus, a +style ``stands for'' a certain key value list. Styles can be parameterized just +like normal code. + +\begin{handler}{{.style}|=|\meta{key list}} + This handler sets things up so that whenever \meta{key}|=|\meta{value} is + encountered in a key list, then the \meta{key list}, with every occurrence + of |#1| replaced by \meta{value}, is processed instead. As always, if no + \meta{value} is given, the default value is used, if defined, or the + special value |\pgfkeysnovalue|. + + You can achieve the same effect by writing + \meta{key}|/.code=\pgfkeysalso{|\meta{key list}|}|. This means, in + particular, that the code of a key could also first execute some normal + code and only then process some further keys. + % +\begin{codeexample}[code only] +\pgfkeys{/par indent/.code={\parindent=#1}} +\pgfkeys{/no indent/.style={/par indent=0pt}} +\pgfkeys{/normal indent/.style={/par indent=2em}} +\pgfkeys{/no indent} +... +\pgfkeys{/normal indent} +\end{codeexample} + % + The following example shows a parameterized style ``in action''. + % +\begin{codeexample}[] +\begin{tikzpicture}[outline/.style={draw=#1,fill=#1!20}] + \node [outline=red] {red box}; + \node [outline=blue] at (0,-1) {blue box}; +\end{tikzpicture} +\end{codeexample} + % +\end{handler} + +\begin{handler}{{.estyle}|=|\meta{key list}} + This handler works like |/.style|, only the \meta{code} is set using + |\edef| rather than |\def|. Thus, all macros in the \meta{code} are + expanded prior to saving the style. +\end{handler} + +For styles the corresponding handlers as for normal code exist: + +\begin{handler}{{.style 2 args}|=|\meta{key list}} + This handler works like |/.code 2 args|, only for styles. Thus, the + \meta{key list} may contain occurrences of both |#1| and |#2| and when the + style is used, two parameters must be given as \meta{value}. + % +\begin{codeexample}[code only] +\pgfkeys{/paper height/.code={\paperheight=#1},/paper width/.code={\paperwidth=#1}} +\pgfkeys{/page size/.style 2 args={/paper height=#1,/paper width=#2}} +\pgfkeys{/page size={30cm}{20cm}} +\end{codeexample} + % +\end{handler} + +\begin{handler}{{.estyle 2 args}|=|\meta{key list}} + This handler works like |/.style 2 args|, only an |\edef| is used rather + than a |\def| to define the macro. +\end{handler} + +\begin{handler}{{.style n args}|=|\marg{argument count}\meta{key list}} + This handler works like |/.code n args|, only for styles. Here, \meta{key + list} may depend on all \meta{argument count} parameters. +\end{handler} + +\begin{handler}{{.add style}|=|\marg{prefix key list}\marg{append key list}} + This handler works like |/.add code|, only for styles. However, it is + permissible to add styles to keys that have previously been set using + |/.code|. (It is also permissible to add normal \meta{code} to a key that + has previously been set using |/.style|). When you add a style to a key + that was previously set using |/.code|, the following happens: When + \meta{key} is processed, the \meta{prefix key list} will be processed + first, then the \meta{code} that was previously stored in + \meta{key}|/.@cmd|, and then the keys in \meta{append key list} are + processed. + % +\begin{codeexample}[code only] +\pgfkeys{/par indent/.code={\parindent=#1}} +\pgfkeys{/par indent/.add style={}{/my key=#1}} +... +\pgfkeys{/par indent=1cm} % This will set \parindent and + % then execute /my key=#1 +\end{codeexample} + % +\end{handler} + +\begin{handler}{{.style args}|=|\marg{argument pattern}\marg{key list}} + This handler works like |/.code args|, only for styles. +\end{handler} + +\begin{handler}{{.estyle args}|=|\marg{argument pattern}\marg{code}} + This handler works like |/.ecode args|, only for styles. +\end{handler} + +\begin{handler}{{.prefix style}|=|\meta{prefix key list}} + Works like |/.add style|, but only for the prefix key list. +\end{handler} + +\begin{handler}{{.append style}|=|\meta{append key list}} + Works like |/.add style|, but only for the append key list. +\end{handler} + + +\subsubsection{Defining Value-, Macro-, If- and Choice-Keys} + +For some keys, the code that should be executed for them is rather +``specialized''. For instance, it happens often that the code for a key just +sets a certain \TeX-if to true or false. For these cases, predefined handlers +make it easier to install the necessary code. + +However, we start with some handlers that are used to manage the value that is +directly stored in a key. + +\begin{handler}{{.initial}|=|\meta{value}} + This handler sets the value of \meta{key} to \meta{value}. Note that no + subkeys are involved. After this handler has been used, by the rules + governing keys, you can subsequently change the value of the \meta{key} by + just writing \meta{key}|=|\meta{value}. Thus, this handler is used to set + the initial value of key. + % +\begin{codeexample}[code only] +\pgfkeys{/my key/.initial=red} +% "/my key" now stores the value "red" +\pgfkeys{/my key=blue} +% "/my key" now stores the value "blue" +\end{codeexample} + + Note that with this configuration, writing |\pgfkeys{/my key}| will not + have the effect you might expect (namely that |blue| is inserted into the + main text). Rather, |/my key| will be promoted to |/my key=\pgfkeysnovalue| + and, thus, |\pgfkeysnovalue| will be stored in |/my key|. + + To retrieve the value stored in a key, the handler |/.get| is used. + + \medskip + \emph{Remark:} A key can both store a value and execute commands% + \footnote{This behavior was partially changed in \pgfname{} 3.1.6 and then + restored in 3.1.7. For compatibility reasons, this behavior will not be + changed in future releases anymore.}. + If so, using \meta{key} will \emph{always} execute commands with the passed + value, or the default value |\pgfkeysnovalue| if no value is provided. + Note that the stored value is never used. To update the stored value, the + handler |/.initial| or command |\pgfkeyssetvalue| is used. + % +\begin{codeexample}[] +\pgfkeys{/my key/.initial=red} +\pgfkeys{/my key/.code=#1} +% "/my key" now both stores the value "red" and executes commands +\pgfkeys{/my key=blue} +% "/my key" now still stores the value "red" +\end{codeexample} + % +\end{handler} + +\begin{handler}{{.get}|=|\meta{macro}} + Executes a |\let| command so that \meta{macro} contains the contents stored + in \meta{key}. + % +\begin{codeexample}[] +\pgfkeys{/my key/.initial=red} +\pgfkeys{/my key=blue} +\pgfkeys{/my key/.get=\mymacro} +\mymacro +\end{codeexample} + % +\end{handler} + +\begin{handler}{{.add}|=|\marg{prefix value}\marg{append value}} + Adds the \meta{prefix value} at the beginning and the \meta{append value} + at the end of the value stored in \meta{key}. +\end{handler} + +\begin{handler}{{.prefix}|=|\marg{prefix value}} + Adds the \meta{prefix value} and the beginning of the value stored in + \meta{key}. +\end{handler} + +\begin{handler}{{.append}|=|\marg{append value}} + Adds the \meta{append value} at the end of the value stored in \meta{key}. +\end{handler} + +\begin{handler}{{.link}|=|\meta{another key}} + Stores the value |\pgfkeysvalueof{|\meta{another key}|}| in the \meta{key}. + The idea is that when you expand the \meta{key}, the value of \meta{another + key} is expanded instead. This corresponds loosely to the notion of soft + links in Unix, hence the name. +\end{handler} + +The next handler is useful for the common situation where +\meta{key}|=|\meta{value} should cause the \meta{value} to be stored in some +macro. Note that, typically, you could just as well store the value in the key +itself. + +\begin{handler}{{.store in}|=|\meta{macro}} + This handler has the following effect: When you write + \meta{key}|=|\meta{value}, the code |\def|\meta{macro}|{|\meta{value}|}| is + executed. Thus, the given value is ``stored'' in the \meta{macro}. + % +\begin{codeexample}[] +\pgfkeys{/text/.store in=\mytext} +\def\a{world} +\pgfkeys{/text=Hello \a!} +\def\a{Gruffalo} +\mytext +\end{codeexample} + % +\end{handler} + +\begin{handler}{{.estore in}|=|\meta{macro}} + This handler is similar to |/.store in|, only the code + |\edef|\meta{macro}|{|\meta{value}|}| is used. Thus, the macro-expanded + version of \meta{value} is stored in the \meta{macro}. + % +\begin{codeexample}[] +\pgfkeys{/text/.estore in=\mytext} +\def\a{world} +\pgfkeys{/text=Hello \a!} +\def\a{Gruffalo} +\mytext +\end{codeexample} + % +\end{handler} + +In another common situation a key is used to set a \TeX-if to true or false. + +\begin{handler}{{.is if}|=|\meta{\TeX-if name}} + This handler has the following effect: When you write + \meta{key}|=|\meta{value}, it is first checked that \meta{value} is |true| + or |false| (the default is |true| if no \meta{value} is given). If this is + not the case, the error key |/errors/boolean expected| is executed. + Otherwise, the code |\|\meta{\TeX-if name}\meta{value} is executed, which + sets the \TeX-if accordingly. + % +\begin{codeexample}[] +\newif\iftheworldisflat +\pgfkeys{/flat world/.is if=theworldisflat} +\pgfkeys{/flat world=false} +\iftheworldisflat + Flat +\else + Round? +\fi +\end{codeexample} + % +\end{handler} + +The next handler deals with the problem when a \meta{key}|=|\meta{value} makes +sense only for a small set of possible \meta{value}s. For instance, the line +cap can only be |rounded| or |rect| or |butt|, but nothing else. For this +situation the following handler is useful. + +\begin{handler}{{.is choice}} + This handler sets things up so that writing \meta{key}|=|\meta{value} will + cause the subkey \meta{key}|/|\meta{value} to be executed. So, each of the + different possible choices should be given by a subkey of \meta{key}. + % +\begin{codeexample}[code only] +\pgfkeys{/line cap/.is choice} +\pgfkeys{/line cap/round/.code={\pgfsetbuttcap}} +\pgfkeys{/line cap/butt/.code={\pgfsetroundcap}} +\pgfkeys{/line cap/rect/.code={\pgfsetrectcap}} +\pgfkeys{/line cap/rectangle/.style={/line cap=rect}} +... +\draw [/line cap=butt] ... +\end{codeexample} + % + If the subkey \meta{key}|/|\meta{value} does not exist, the error key + |/errors/unknown choice value| is executed. +\end{handler} + + +\subsubsection{Expanded and Multiple Values} + +When you write \meta{key}|=|\meta{value}, you usually wish to use the +\meta{value} ``as is''. Indeed, great care is taken to ensure that you can even +use things like |#1| or unbalanced \TeX-ifs inside \meta{value}. However, +sometimes you want the \meta{value} to be expanded before it is used. For +instance, \meta{value} might be a macro name like |\mymacro| and you do not +want |\mymacro| to be used as the macro, but rather the \emph{contents} of +|\mymacro|. Thus, instead of using \meta{value}, you wish to use whatever +\meta{value} expands to. Instead of using some fancy |\expandafter| hackery, +you can use the following handlers: + +\begin{handler}{{.expand once}|=|\meta{value}} + This handler expands \meta{value} once (more precisely, it executes an + |\expandafter| command on the first token of \meta{value}) and then process + the resulting \meta{result} as if you had written + \meta{key}|=|\meta{result}. Note that if \meta{key} contains a handler + itself, this handler will be called normally. + % +\begin{codeexample}[] +\def\a{bottom} +\def\b{\a} +\def\c{\b} + +\pgfkeys{/key1/.initial=\c} +\pgfkeys{/key2/.initial/.expand once=\c} +\pgfkeys{/key3/.initial/.expand twice=\c} +\pgfkeys{/key4/.initial/.expanded=\c} + +\def\a{{\ttfamily\string\a}} +\def\b{{\ttfamily\string\b}} +\def\c{{\ttfamily\string\c}} + +\begin{tabular}{ll} +Key 1:& \pgfkeys{/key1} \\ +Key 2:& \pgfkeys{/key2} \\ +Key 3:& \pgfkeys{/key3} \\ +Key 4:& \pgfkeys{/key4} +\end{tabular} +\end{codeexample} + % +\end{handler} + +\begin{handler}{{.expand twice}|=|\meta{value}} + This handler works like saying + \meta{key}|/.expand once/.expand once=|\meta{value}. +\end{handler} + +\begin{handler}{{.expanded}|=|\meta{value}} + This handler will completely expand \meta{value} (using |\edef|) before + processing \meta{key}|=|\meta{result}. +\end{handler} + +\begin{handler}{{.evaluated}|=|\meta{value}} + This handler will evaluate \meta{value} as a mathematical + expression with |\pgfmathparse| and assign \meta{key}|=\pgfmathresult|. + % +\begin{codeexample}[] +\pgfkeys{ + /golden ratio/.initial/.evaluated={(1 + sqrt(5))/2}, +} +\pgfkeys{/golden ratio} +\end{codeexample} + % +\end{handler} + +\begin{handler}{{.list}|=|\meta{comma-separated list of values}} + This handler causes the key to be used repeatedly, namely once for every + element of the list of values. Note that the list of values should + typically be surrounded by braces since, otherwise, \TeX\ will not be able + to tell whether a comma starts a new key or a new value. + + The \meta{list of values} is processed using the |\foreach| statement, so + you can use the |...| notation. + % +\begin{codeexample}[] +\pgfkeys{/foo/.code=(#1)} +\pgfkeys{/foo/.list={a,b,0,1,...,5}} +\end{codeexample} + % +\end{handler} + + +\subsubsection{Handlers for Forwarding} + +\begin{handler}{{.forward to}|=|\meta{another key}} + This handler causes the \meta{key} to ``forward'' its argument to + \meta{another key}. When the \meta{key} is used, its normal code will be + executed first. Then, the value is (additionally) passed to \meta{another + key}. If the \meta{key} has not yet been defined prior to the use of + |.forward to|, it will be defined then (and do nothing by itself, expect + for forwarding it to \meta{key name}). The \meta{another key} must be a + fully qualified key name. + % +\begin{codeexample}[] +\pgfkeys{ + /a/.code=(a:#1), + /b/.code=(b:#1), + /b/.forward to=/a, + /c/.forward to=/a +} +\pgfkeys{/b=1} \pgfkeys{/c=2} +\end{codeexample} + % +\end{handler} + +\begin{handler}{{.search also}=\marg{path list}} + A style which installs a |/.unknown| handler into \meta{key}. This + |/.unknown| handler will then search for unknown keys in every path + provided in \marg{path list}. + % +\begin{codeexample}[] +% define a key: +\pgfkeys{/secondary path/option/.code={Invoking /secondary path/option with `#1'}} + +% set up a search path: +\pgfkeys{/main path/.search also={/secondary path}} + +% try searching for `option=value' in '/main path': +% -> this finds `/secondary path/option'! +\pgfkeys{/main path/.cd,option=value} +\end{codeexample} + + The |/.search also| handler follows the strategy + % + \begin{enumerate} + \item If a user provides a fully qualified key which could not be + found, for example the full string |/main path/option|, it assumes + that the user knew what she is doing -- and does \emph{not} + continue searching for |option| in \marg{path list}. + \item If a user provides only the key's name, for example |option| and + |option| cannot be found in the current default path (which is + |/main path| in our example above), the current default path is set + to the next element in \marg{path list} (which is |/secondary path| + here) and |\pgfkeys| will be restarted. + + This will be iterated until either a match has been found or all + elements in \marg{path list} have been tested. + \item If all + elements in \marg{path list} have been checked and the key is still + unknown, the fall-back handler |/handlers/.unknown| will be + invoked. + \end{enumerate} + % +\begin{codeexample}[] +% define a key: +\pgfkeys{/secondary path/option/.code={Invoking /secondary path/option with `#1'}} + +% set up a search path: +\pgfkeys{/main path/.search also={/secondary path}} + +% try searching for `option=value' in '/main path': +% -> this finds `/secondary path/option'! +\pgfkeys{/main path/.cd,option=value} + +% negative example: +% try searching for fully qualified key /main path/option. +% This won't be handled by .search also. +\pgfkeys{/handlers/.unknown/.code={Found unknown option \pgfkeyscurrentkeyRAW={#1}!}}% +\pgfkeys{/main path/.cd,/main path/option=value} +\end{codeexample} + + Please note that the strategy of |/.search also| is different from the + first example provided in section~\ref{sec:pgf:unknown:keys} ``Unknown + Keys'' because |/.search also| only applies to keys that are not fully + qualified. + + For those who are familiar with |\pgfkeys|, the actual implementation of + |/.search also| might be interesting: + % + \begin{enumerate} + \item |\pgfkeys{/path/.search also={/tikz}}| is equivalent to + % +\begin{codeexample}[code only] +\pgfkeys{/path/.unknown/.code={% + \def\pgfkeys@searchalso@temp@value{#1}% + \ifpgfkeysaddeddefaultpath + \expandafter\pgfkeys@firstoftwo + \else + \expandafter\pgfkeys@secondoftwo + \fi{% + % only process keys for which no full path has been + % provided: + \pgfkeyssuccessfalse + \let\pgfkeys@searchalso@name=\pgfkeyscurrentkeyRAW + \ifpgfkeyssuccess + \else + % search with /tikz as default path: + \pgfqkeys{/tikz}{\pgfkeys@searchalso@name/.expand once=% + \pgfkeys@searchalso@temp@value}% + \fi + }{% + \pgfkeysgetvalue{/handlers/.unknown/.@cmd}{\pgfkeys@code}% + \expandafter\pgfkeys@code\pgfkeys@searchalso@temp@value\pgfeov + }% + } +} +\end{codeexample} + % + \item |\pgfkeys{/path/.search also={/tikz,/pgf}}| is equivalent to + % +\begin{codeexample}[code only] +\pgfkeys{/path/.unknown/.code={% + \def\pgfkeys@searchalso@temp@value{#1}% + \ifpgfkeysaddeddefaultpath + \expandafter\pgfkeys@firstoftwo + \else + \expandafter\pgfkeys@secondoftwo + \fi{% + \pgfkeyssuccessfalse + \let\pgfkeys@searchalso@name=\pgfkeyscurrentkeyRAW + \ifpgfkeyssuccess + \else + % step 1: search in /tikz with .try: + \pgfqkeys{/tikz}{\pgfkeys@searchalso@name/.try/.expand once=% + \pgfkeys@searchalso@temp@value}% + \fi + \ifpgfkeyssuccess + \else + % step 2: search in /pgf (without .try!): + \pgfqkeys{/pgf}{\pgfkeys@searchalso@name/.expand once=\pgfkeys@searchalso@}% + \fi + }{% + \pgfkeysgetvalue{/handlers/.unknown/.@cmd}{\pgfkeys@code}% + \expandafter\pgfkeys@code\pgfkeys@searchalso@temp@value\pgfeov + }% + } +} +\end{codeexample} + \end{enumerate} + + To also enable searching for styles (or other handled keys), consider + changing the configuration for handled keys to + |/handler config=full or existing| when you use |/.search also|, that is, + use + % +\begin{codeexample}[code only] +\pgfkeys{ + /main path/.search also={/secondary path}, + /handler config=full or existing} +\end{codeexample} + % +\end{handler} + + +\subsubsection{Handlers for Testing Keys} + +\begin{handler}{{.try}|=|\meta{value}} + This handler causes the same things to be done as if + \meta{key}|=|\meta{value} had been written instead. However, if neither + \meta{key}|/.@cmd| nor the key itself is defined, no handlers will be + called. Instead, the execution of the key just stops. Thus, this handler + will ``try'' to use the key, but no further action is taken when the key is + not defined. + + The \TeX-if |\ifpgfkeyssuccess| will be set according to whether the + \meta{key} was successfully executed or not. + % +\begin{codeexample}[] +\pgfkeys{/a/.code=(a:#1)} +\pgfkeys{/b/.code=(b:#1)} +\pgfkeys{/x/.try=hmm,/a/.try=hallo,/b/.try=welt} +\end{codeexample} + % +\end{handler} + +\begin{handler}{{.retry}|=|\meta{value}} + This handler works just like |/.try|, only it will not do anything if + |\ifpgfkeyssuccess| is false. Thus, this handler will only retry to set a + key if ``the last attempt failed''. + % +\begin{codeexample}[] +\pgfkeys{/a/.code=(a:#1)} +\pgfkeys{/b/.code=(b:#1)} +\pgfkeys{/x/.try=hmm,/a/.retry=hallo,/b/.retry=welt} +\end{codeexample} + % +\end{handler} + +\begin{handler}{{.lastretry}|=|\meta{value}} + This handler works like |/.retry|, only it will invoke the usual handlers + for unknowns keys if |\ifpgfkeyssuccess| is false. Thus, this handler + will only try to set a key if ``the last attempt failed''. Furthermore, + this here is the last such attempt. +\end{handler} + + +\subsubsection{Handlers for Key Inspection} + +\begin{handler}{{.show value}} + This handler executes a |\show| command on the value stored in \meta{key}. + This is useful mostly for debugging. + + \example |\pgfkeys{/my/obscure key/.show value}| +\end{handler} + +\begin{handler}{{.show code}} + This handler executes a |\show| command on the code stored in + \meta{key}|/.@cmd|. This is useful mostly for debugging. + + \example |\pgfkeys{/my/obscure key/.show code}| +\end{handler} + +The following key is not a handler, but it also commonly used for inspecting +things: +% +\begin{key}{/utils/exec=\meta{code}} + This key will simply execute the given \meta{code}. + + % FIXME: there is a bug in the pretty printer ... fix it! + \example \verb|\pgfkeys{some key=some value,/utils/exec=\show\hallo,obscure key=obscure}| +\end{key} + + +\subsection{Error Keys} + +In certain situations errors can occur, like using an undefined key. In these +situations error keys are executed. They should store a macro that gets two +arguments: The first is the offending key (possibly only after macro +expansion), the second is the value that was passed as a parameter (also +possibly only after macro expansion). + +Currently, error keys are simply executed. In the future it might be a good +idea to have different subkeys that are executed depending on the language +currently set so that users get a localized error message. + +\begin{key}{/errors/value required=\marg{offending key}\marg{value}} + This key is executed whenever an \meta{offending key} is used without a + value when a value is actually required. +\end{key} + +\begin{key}{/errors/value forbidden=\marg{offending key}\marg{value}} + This key is executed whenever a key is used with a value when a value is + actually forbidden. +\end{key} + +\begin{key}{/errors/boolean expected=\marg{offending key}\marg{value}} + This key is executed whenever a key set up using |/.is if| gets called with + a \meta{value} other than |true| or |false|. +\end{key} + +\begin{key}{/errors/unknown choice value=\marg{offending key}\marg{value}} + This key is executed whenever a choice is used as a \meta{value} for a key + set up using the |/.is choice| handler that is not defined. +\end{key} + +\begin{key}{/errors/unknown key=\marg{offending key}\marg{value}} + This key is executed whenever a key is unknown and no specific |/.unknown| + handler is found. +\end{key} + + +\input{pgfmanual-en-pgfkeysfiltered.tex} |