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diff --git a/Master/texmf-dist/doc/generic/pgf/pgfmanual-en-oo.tex b/Master/texmf-dist/doc/generic/pgf/pgfmanual-en-oo.tex new file mode 100644 index 00000000000..66ddbc6c4a7 --- /dev/null +++ b/Master/texmf-dist/doc/generic/pgf/pgfmanual-en-oo.tex @@ -0,0 +1,690 @@ +% Copyright 2018 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{Object-Oriented Programming} +\label{section-oop} + +This section describes the |oo| module. + +\begin{pgfmodule}{oo} + This module defines a relatively small set of \TeX\ commands for defining + classes, methods, attributes and objects in the sense of object-oriented + programming. +\end{pgfmodule} + +In this chapter it is assumed that you are familiar with the basics of a +typical object-oriented programming language like Java, C++ or Eiffel. + + +\subsection{Overview} + +\TeX\ does not support object-oriented programming, presumably because it was +written at a time when this style of programming was not yet ``en vogue''. When +one is used to the object-oriented style of thinking, some programming +constructs in \TeX\ often seem overly complicated. The object-oriented +programming module of \pgfname\ may help here. It is written completely using +simple \TeX\ macros and is, thus, perfectly portable. This also means, however, +that it is not particularly fast (but not too slow either), so you should use +it only for non-time-critical things. + +Basically, the oo-system supports \emph{classes} (in the object-oriented sense, +this has nothing to do with \LaTeX-classes), \emph{methods}, +\emph{constructors}, \emph{attributes}, \emph{objects}, \emph{object +identities}, and (thanks to Sa\v so \v Zivanovi\'c) \emph{inheritance} and +\emph{overloading.} + +The first step is to define a class, using the macro |\pgfooclass| (all normal +macros in \pgfname's object-oriented system start with |\pgfoo|). This macro +gets the name of a class and in its body a number of \emph{methods} are +defined. These are defined using the |\method| macro (which is defined only +inside such a class definition) and they look a bit like method definitions in, +say, Java. Object attributes are declared using the |\attribute| command, which +is also defined only inside a class definition. + +Once a class has been defined, you can create objects of this class. Objects +are created using |\pgfoonew|. Such an object has many characteristics of +objects in a normal object-oriented programming language: Each object has a +\emph{unique identity}, so when you create another object, this object is +completely distinct from all other objects. Each object also has a set of +private attributes, which may change over time. Suppose, for instance, that we +have a |point| class. Then creating a new object (called an instance) of this +class would typically have an |x|-attribute and a |y|-attribute. These can be +changed over time. Creating another instance of the |point| class creates +another object with its own |x|- and |y|-attributes. + +Given an object, you can call a method for this object. Inside the method the +attributes of the object for which the method is being called can be accessed. + +The life of an object always ends with the end of the \TeX\ scope in which it +was created. However, changes to attribute values are not local to scopes, so +when you change an attribute anywhere, this change persists till the end of the +life of the object or until the attribute is changed again. + + +\subsection{A Running Example: The Stamp Class} + +As a running example we will develop a |stamp| class and |stamp| objects. The +idea is that a stamp object is able to ``stamp something'' on a picture. This +means that a stamp object has an attribute storing the ``stamp text'' and there +is a method that asks the object to place this text somewhere on a canvas. The +method can be called repeatedly and there can be several different stamp +objects, each producing a different text. Stamp objects can either be created +dynamically when needed or a library might define many such objects in an outer +scope. + +Such stamps are similar to many things present in \pgfname\ such as arrow tips, +patterns, or shadings and, indeed, these could all have been implemented in +this object-oriented fashion (which might have been better, but the +object-oriented subsystem is a fairly new addition to \pgfname). + + +\subsection{Classes} + +We start with the definition of the |stamp| class. This is done using the +|\pgfooclass| macro: + +\begin{command}{\pgfooclass\opt{|(|\meta{list of superclasses}|)|}\marg{class name}\marg{body}} + This command defines a class named \meta{class name}. The name of the class + can contain spaces and most other characters, but no periods. So, valid + class names are |MyClass| or |my class| or |Class_C++_emulation??1|. The + \meta{list of superclasses} is optional just like the parenthesis around + it. + + The \meta{body} is actually just executed, so any normal \TeX-code is + permissible here. However, while the \meta{body} is being executed, the + macros |\method| and |\attribute| are set up so that they can be used to + define methods and attributes for this class (the original meanings are + restored afterward). + + The definition of a class is local to the scope where the class has been + defined. + % +\begin{codeexample}[code only] +\pgfooclass{stamp}{ + % This is the class stamp + + \attribute text; + \attribute rotation angle=20; + + \method stamp(#1) { % The constructor + ... + } + + \method apply(#1,#2) { % Causes the stamp to be shown at coordinate (#1,#2) + ... + } +} + +% We can now create objects of type "stamp" +\end{codeexample} + + Concerning the list of base classes, the Method Resolution Order + (\textsc{mro}) is computed using the C3 algorithm also used in Python, v2.3 + and higher. The linearization computed by the algorithm respects both + local precedence ordering and monotonicity. Resolution of both methods and + attributes depends on the \textsc{mro}: when a method method name is called + on an object of class $C$, the system invokes method method name from the + first class in the \textsc{mro} of $C$ which defines method method name; + when an object is created, each attribute |attr| is initialized to the + value specified in the first class in the \textsc{mro} of $C$ which + declares attribute |attr|. +\end{command} + +The \meta{body} of a class usually just consists of calls to the macros +|\attribute| and |\method|, which will be discussed in more detail in later +sections. + + +\subsection{Objects} + +Once a class has been declared, we can start creating objects for this class. +For this the |\pgfoonew| command can be used, which has a peculiar syntax: + +\begin{command}{\pgfoonew\opt{\meta{object handle or attribute}|=|}|new |\meta{class name}|(|\meta{constructor arguments}|)|} + Causes a new object to be created. The class of the object will be + \meta{class name}, which must previously have been declared using + |\pgfooclass|. Once the object has been created, the constructor method of + the object will be called with the parameter list set to \meta{constructor + arguments}. + + The resulting object is stored internally and its lifetime will end exactly + at the end of the current scope. + + Here is an example in which three stamp objects are created. + % +\begin{codeexample}[code only] +\pgfoonew \firststamp=new stamp() +\pgfoonew \secondstamp=new stamp() +{ + \pgfoonew \thirdstamp=new stamp() + ... +} +% \thirdstamp no longer exists, but \firststamp and \secondstamp do +% even if you try to store \thirdstamp in a global variable, trying +% to access it will result in an error. +\end{codeexample} + + The optional \meta{object handle or attribute} can either be an + \meta{object handle} or an \meta{attribute}. When an \meta{object handle} + is given, it must be a normal \TeX\ macro name that will ``point'' to the + object (handles are discussed in more detail in + Section~\ref{section-identities}). You can use this macro to call methods + of the object as discussed in the following section. When an + \meta{attribute} is given, it must be given in curly braces (the curly + braces are used to detect the presence of an attribute). In this case, a + handle to the newly created object is stored in this attribute. + % +\begin{codeexample}[code only] +\pgfooclass{foo} +{ + \attribute stamp obj; + \attribute another object; + + \method foo() { + \pgfoonew{stamp obj}=new stamp() + \pgfoonew{another object}=new bar() + } + ... +} +\end{codeexample} + % +\end{command} + +\begin{command}{\pgfoogc} + This command causes the ``garbage collector'' to be invoked. The job of + this garbage collector is to free the global \TeX-macros that are used by + ``dead'' objects (objects whose life-time has ended). This macro is called + automatically after every scope in which an object has been created, so you + normally do not need to call this macro yourself. +\end{command} + + +\subsection{Methods} + +Methods are defined inside the body of classes using the following command: + +\begin{command}{\method \meta{method name}|(|\meta{parameter list}|)|\marg{method body}} + This macro, which is only defined inside a class definition, defines a new + method named \meta{method name}. Just like class names, method names can + contain spaces and other characters, so \meta{method names} like + |put_stamp_here| or |put stamp here| are both legal. + + Three method names are special: First, a method having either the same name + as the class or having the name |init| is called the \emph{constructor} of + the class. There are (currently) no destructors; objects simply become + ``undefined'' at the end of the scope in which they have been created. The + other two methods are called |get id| and |get handle|, which are always + automatically defined and which you cannot redefine. They are discussed in + Section~\ref{section-identities}. + + Overloading of methods by differing numbers of parameters is not possible, + that is, it is illegal to have two methods inside a single class with the + same name (despite possibly different parameter lists). However, two + different classes may contain a method with the same name, that is, classes + form namespaces for methods. Also, a class can (re)implement a method from + a superclass. + + The \meta{method name} must be followed by a \meta{parameter list} in + parentheses, which must be present even when the \meta{parameter list} is + empty. The \meta{parameter list} is actually a normal \TeX\ parameter list + that will be matched against the parameters inside the parentheses upon + method invocation and, thus, could be something like |#1#2 foo #3 bar.|, + but a list like |#1,#2,#3| is more customary. By setting the parameter list + to just |#1| and then calling, say, |\pgfkeys{#1}| at the beginning of a + method, you can implement Objective-C-like named parameters. + + When a method is called, the \meta{body} of the method will be executed. + The main difference to a normal macro is that while the \meta{body} is + executed, a special macro called |\pgfoothis| is set up in such a way that + it references the object for which the method is executed. +\end{command} + +In order to call a method for an object, you first need to create the object +and you need a handle for this object. In order to invoke a method for this +object, a special syntax is used that is similar to Java or C++ syntax: + +\begin{pgfmanualentry} + \pgfmanualentryheadline{\meta{object handle}\opt{|.|\meta{super class}}|.|\meta{method name}|(|\meta{parameters}|)|}% + \pgfmanualbody + This causes the method \meta{method name} to be called for the object + referenced by the \meta{object handle}. The method is the one defined in + the class of the object or, if it is not defined there, the method defined + in the superclasses of the object's class (if there are several + superclasses that define the same method, the method resolution order is + used to determine which one gets called). If the optional \meta{super + class} is specified, the method implementation of that class will be used + rather than the implementation in the object's class. The \meta{parameters} + are matched against the parameters of the method and, then, the method body + is executed. The execution of the method body is \emph{not} done inside a + scope, so the effects of a method body persist. + % +\begin{codeexample}[code only] +\pgfooclass{stamp}{ + % This is the class stamp + + \method stamp() { % The constructor + } + + \method apply(#1,#2) { % Causes the stamp to be shown at coordinate (#1,#2) + % Draw the stamp: + \node [rotate=20,font=\huge] at (#1,#2) {Passed}; + } +} + +\pgfoonew \mystamp=new stamp() + +\begin{tikzpicture} + \mystamp.apply(1,2) + \mystamp.apply(3,4) +\end{tikzpicture} +\end{codeexample} + + Inside a method, you can call other methods. If you have a handle for + another object, you can simply call it in the manner described above. In + order to call a method of the current object, you can use the special + object handle |\pgfoothis|. + + \begin{command}{\pgfoothis} + This object handle is well-defined only when a method is being executed. + There, it is then set to point to the object for which the method is + being called, which allows you to call another method for the same + object. + % +\begin{codeexample}[code only] +\pgfooclass{stamp}{ + % This is the class stamp + + \method stamp() {} + + \method apply(#1,#2) { + \pgfoothis.shift origin(#1,#2) + + % Draw the stamp: + \node [rotate=20,font=\huge] {Passed}; + } + + % Private method: + \method shift origin(#1,#2) { + \tikzset{xshift=#1,yshift=#2} + } +} +\end{codeexample} + \end{command} +\end{pgfmanualentry} + +\begin{command}{\pgfoosuper|(|\meta{class},\meta{object handle}|).|\meta{method name}|(|\meta{arguments}|)|} + This macro gives you finer control over which method gets invoked in case + of multiple inheritance. This macro calls \meta{method name} of the object + specified by \meta{object handle}, but which implementation of the method + is called is determined as follows: it will be the implementation in the + first class (in the method resolution order) after \meta{class} that + defines \meta{method name}. +\end{command} + + +\subsection{Attributes} + +Every object has a set of attributes, which may change over time. Attributes +are declared using the |\attribute| command, which, like the |\method| command, +is defined only inside the scope of |\pgfooclass|. Attributes can be modified +(only) by methods. To take the |stamp| example, an attribute of a |stamp| +object might be the text that should be stamped when the |apply| method is +called. + +When an attribute is changed, this change is \emph{not} local to the current +\TeX\ group. Changes will persist till the end of the object's life or until +the attribute is changed once more. + +To declare an attribute you should use the |\attribute| command: +% +\begin{command}{\attribute \meta{attribute name}\opt{|=|\meta{initial value}}|;|} + This command can only be given inside the body of an |\pgfooclass| command. + It declares the attribute named \meta{attribute name}. This name, like + method or class names, can be quite arbitrary, but should not contain + periods. Valid names are |an_attribute?| or |my attribute|. + + You can optionally specify an \meta{initial value} for the attribute; if + none is given, the empty string is used automatically. The initial value is + the value that the attribute will have just after the object has been + created and before the constructor is called. + % +\begin{codeexample}[code only] +\pgfooclass{stamp}{ + % This is the class stamp + + \attribute text; + \attribute rotation angle = 20; + + \method stamp(#1) { + \pgfooset{text}{#1} % Set the text + } + + \method apply(#1,#2) { + \pgfoothis.shift origin(#1,#2) + + % Draw the stamp: + \node [rotate=\pgfoovalueof{rotation angle},font=\huge] + {\pgfoovalueof{text}}; + } + + \method shift origin(#1,#2) { ... } + + \method set rotation (#1) { + \pgfooset{rotation angle}{#1} + } +} +\end{codeexample} + % +\end{command} + +Attributes can be set and read only inside methods, it is not possible to do so +using an object handle. Spoken in terms of traditional object-oriented +programming, attributes are always private. You need to define getter and +setter methods if you wish to read or modify attributes. + +Reading and writing attributes is not done using the ``dot-notation'' that is +used for method calls. This is mostly due to efficiency reasons. Instead, a set +of special macros is used, all of which can \emph{only be used inside methods}. + +\begin{command}{\pgfooset\marg{attribute}\marg{value}} + Sets the \meta{attribute} of the current object to \meta{value}. + % +\begin{codeexample}[code only] +\method set rotation (#1) { + \pgfooset{rotation angle}{#1} +} +\end{codeexample} + % +\end{command} + +\begin{command}{\pgfooeset\marg{attribute}\marg{value}} + Performs the same action as |\pgfooset| but in an |\edef| full expansion + context. +\end{command} + +\begin{command}{\pgfooappend\marg{attribute}\marg{value}} + This method adds the given \meta{value} to the \meta{attribute} at the end. +\end{command} + +\begin{command}{\pgfooprefix\marg{attribute}\marg{value}} + This method adds the given \meta{value} to the \meta{attribute} at the + beginning. +\end{command} + +\begin{command}{\pgfoolet\marg{attribute}\marg{macro}} + Sets the \meta{attribute} of the current value to the current value of + \meta{macro} using \TeX's |\let| command. + % +\begin{codeexample}[code only] +\method foo () { + \pgfoolet{my func}\myfunc + % Changing \myfunc now has no effect on the value of attribute my func +} +\end{codeexample} + % +\end{command} + +\begin{command}{\pgfoovalueof\marg{attribute}} + Expands (eventually) to the current value of \meta{attribute} of the + current object. + % +\begin{codeexample}[code only] +\method apply(#1,#2) { + \pgfoothis.shift origin(#1,#2) + + \node [rotate=\pgfoovalueof{rotation angle},font=\huge] + {\pgfoovalueof{text}}; +} +\end{codeexample} + % +\end{command} + +\begin{command}{\pgfooget\marg{attribute}\marg{macro}} + Reads the current value of \meta{attribute} and stores the result in + \meta{macro}. + % +\begin{codeexample}[code only] +... + \method get rotation (#1) { + \pgfooget{rotation angle}{#1} + } +... + +\mystamp.get rotation(\therotation) +``\therotation'' is now ``20'' (or whatever). +\end{codeexample} + % +\end{command} + + +\subsection{Identities} +\label{section-identities} + +Every object has a unique identity, which is simply an integer. It is possible +to retrieve the object id using the |get id| method (discussed below), but +normally you will not need to do so because the id itself cannot be used to +access an object. Rather, you access objects via their methods and these, in +turn, can only be called via object handles. + +Object handles can be created in four ways: +% +\begin{enumerate} + \item Calling |\pgfoonew|\meta{object handle}|=...| will cause \meta{object + handle} to be a handle to the newly created object. + \item Using |\let| to create an alias of an existing object handle: If + |\mystamp| is a handle, saying |\let\myotherstamp=\mystamp| creates a + second handle to the same object. + \item |\pgfooobj|\marg{id} can be used as an object handle to the object + with the given \meta{id}. + \item Using the |get handle| method to create a handle to a given object. +\end{enumerate} + +Let us have a look at the last two methods. + +\begin{command}{\pgfooobj\marg{id}} + Provided that \meta{id} is the id of an existing object (an object whose + life-time has not expired), calling this command yields a handle to this + object. The handle can then be used to call methods: + % +\begin{codeexample}[code only] +% Create a new object: +\pgfoonew \mystamp=new stamp() + +% Get the object's id and store it in \myid: +\mystamp.get id(\myid) + +% The following two calls have the same effect: +\mystamp.apply(1,1) +\pgfooobj{\myid}.apply(1,1) +\end{codeexample} + % +\end{command} + +The |get id| method can be used to retrieve the id of an object. This method is +predefined for every class and you should not try to define a method of this +name yourself. + +\begin{predefinedmethod}{get id(\meta{macro})} + Calling \meta{obj}|.get id(|\meta{macro}|)| stores the id \meta{obj} in + \meta{macro}. This is mainly useful when you wish to store an object for a + longer time and you cannot guarantee that any handle that you happen to + have for this object will be available later on. + + The only way to use the retrieved id later on is to call |\pgfooobj|. + + Different object that are alive (that are still within the scope in which + they were created) will always have different ids, so you can use the id to + test for equality of objects. However, after an object has been destroyed + because its scope has ended, the same id may be used again for newly + created objects. + + Here is a typical application where you need to call this method: You wish + to collect a list of objects for which you wish to call a specific method + from time to time. For the collection process you wish to offer a macro + called |\addtoobjectlist|, which takes an object handle as parameter. It is + quite easy to store this handle somewhere, but a handle is, well, just a + handle. Typically, shortly after the call to |\addtoobjectlist| the handle + will no longer be valid or even exist, even though the object still exists. + In this case, you wish to store the object id somewhere instead of the + handle. Thus, for the object passed to |\addtoobjectlist| you call the + |get id| method and store the resulting id, rather than the handle. +\end{predefinedmethod} + +There is a second predefined method, called |get handle|, which is also used to +create object handles. + +\begin{predefinedmethod}{get handle(\marg{macro name})} + Calling this method for an object will cause \meta{macro name} to become a + handle to the given object. For any object handle |\obj| -- other than + |\pgfoothis| -- the following two have the same effect: + % + \begin{enumerate} + \item |\let|\meta{macro name}|=\obj| + \item |\obj.get handle(|\meta{macro name}|)| + \end{enumerate} + + The first method is simpler and faster. However, for |\pgfoothis| there is + a difference: The call |\pgfoothis.get handle(|\meta{macro name}|)| will + cause \meta{macro name} to be an object handle to the current object and + will persist to be so even after the method is done. By comparison, + |\let|\meta{macro name}|=\pgfoothis| causes |\obj| to be the same as the + very special macro |\pgfoothis|, so |\obj| will always refer to the current + object, which may change over time. +\end{predefinedmethod} + + +\subsection{The Object Class} +\label{section-object} + +The object-oriented module predefines a basic class |object| that can be used +as a base class in different context. + +\begin{ooclass}{object} + This class current only implements one method: + + \begin{method}{copy(\meta{handle})} + Creates a new object and initializes the values of its (declared) + attributes to the values of the original. The method takes one + argument: a control sequence which receives the handle of the copy. + \end{method} +\end{ooclass} + + +\subsection{The Signal Class} +\label{section-signals} + +In addition to the basic mechanism for defining and using classes and object, +the class |signal| is predefined. It implements a so-called signal--slot +mechanism. + +\begin{ooclass}{signal} + This class is used to implement a simple signal--slot mechanism. The idea + is the following: From time to time special things happen about which a + number of objects need to be informed. Different things can happen and + different object will be interested in these things. A |signal| object can + be used to signal that such special things of a certain kind have happened. + For example, one signal object might be used to signal the event that ``a + page has been shipped out''. Another signal might be used to signal that + ``a figure is about to be typeset'', and so on. + + Objects can ``tune in'' to signals. They do so by \emph{connecting} one of + their methods (then called a \emph{slot}) to the signal. Then, whenever the + signal is \emph{emitted}, the method of the connected object(s) get called. + Different objects can connect different slots to the same signal as long as + the argument lists will fit. For example, the object that is used to signal + the ``end of page has been reached'' might emit signals that have, say, the + box number in which the finished page can be found as a parameter + (actually, the finished page is always in box 255). Then one object could + connect a method |handle page(#1)| to this signal, another might connect + the method |emergency action(#1)| to this signal, and so on. + + Currently, it is not possible to ``unregister'' or ``detach'' a slot from a + signal, that is, once an object has been connect to a signal, it will + continue to receive emissions of this signal till the end of the life-time + of the signal. This is even true when the object no longer exists (but the + signal does), so care must be taken that signal objects are always created + after the objects that are listening to them. + + \begin{method}{signal()} + The constructor does nothing. + \end{method} + + \begin{method}{connect(\meta{object handle},\meta{method name})} + This method gets an \meta{object handle} as parameter and a + \meta{method name} of this object. It will queue the object-method pair + in an internal list and each time the signal emits something, this + object's method is called. + + Be careful not to pass |\pgfoothis| as \meta{object handle}. This would + cause the signal object to connect to itself. Rather, if you wish to + connect a signal to a method of the current object you first need to + create an alias using the |get handle| method: + % +\begin{codeexample}[code only] +\pgfooclass{some class}{ + \method some class() { + \pgfoothis.get handle(\me) + \somesignal.connect(\me,foo) + \anothersignal.connect(\me,bar) + } + \method foo () {} + \method bar (#1,#2) {} +} +\pgfoonew \objA=new some class() +\pgfoonew \objB=new some class() +\end{codeexample} + \end{method} + + \begin{method}{emit(\meta{arguments})} + This method emits a signal to all connected slots. This means that for + all objects that have previously been connected via a call of + |connect|, the method (slot) that was specified during the call of + |connect| is invoked with given \meta{arguments}. + % +\begin{codeexample}[code only] +\anothersignal.emit(1,2) +% will call \objA.bar(1,2) and \objB.bar(1,2) +\end{codeexample} + \end{method} +\end{ooclass} + + +\subsection{Implementation Notes} + +For the curious, here are some notes on how the oo-system is implemented: +% +\begin{itemize} + \item There is an object id counter that gets incremented each time an + object is created. However, this counter is local to the current scope, + which means that it is reset at the end of each scope, corresponding to + the fact that at the end of a scope all objects created in this scope + become invalid. Newly created objects will then have the same id as + ``deleted'' objects. + \item Attributes are stored globally. For each attribute of each object + there is a macro whose name is composed of the object's id and the + attribute name. Changes to object attributes are always global. + \item A call to the garbage collector causes a loop to be executed that + tries to find objects whose object number is larger than the current + maximum alive objects. The global attributes of these objects are then + freed (set to |\relax|) by calling a special internal method of these + (dead) objects. + + The garbage collector is automatically called after each group in + which an object was created using |\aftergroup|. + \item When a method is called, before the method call some code is executed + that sets a global counter storing the current object id to the object + id of the object being called. After the method call some code is + inserted that restores the global counter to its original value. This + is done without scopes, so some tricky |\expandafter| magic is needed. + Note that, because of this process, you cannot use commands like + |\pgfutil@ifnextchar| at the end of a method. + \item An object handle contains just the code to set up and restore the + current object number to the number of the object being called. +\end{itemize} |