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+=head1 NAME
+X<reference> X<pointer> X<data structure> X<structure> X<struct>
+
+perlref - Perl references and nested data structures
+
+=head1 NOTE
+
+This is complete documentation about all aspects of references.
+For a shorter, tutorial introduction to just the essential features,
+see L<perlreftut>.
+
+=head1 DESCRIPTION
+
+Before release 5 of Perl it was difficult to represent complex data
+structures, because all references had to be symbolic--and even then
+it was difficult to refer to a variable instead of a symbol table entry.
+Perl now not only makes it easier to use symbolic references to variables,
+but also lets you have "hard" references to any piece of data or code.
+Any scalar may hold a hard reference. Because arrays and hashes contain
+scalars, you can now easily build arrays of arrays, arrays of hashes,
+hashes of arrays, arrays of hashes of functions, and so on.
+
+Hard references are smart--they keep track of reference counts for you,
+automatically freeing the thing referred to when its reference count goes
+to zero. (Reference counts for values in self-referential or
+cyclic data structures may not go to zero without a little help; see
+L<perlobj/"Two-Phased Garbage Collection"> for a detailed explanation.)
+If that thing happens to be an object, the object is destructed. See
+L<perlobj> for more about objects. (In a sense, everything in Perl is an
+object, but we usually reserve the word for references to objects that
+have been officially "blessed" into a class package.)
+
+Symbolic references are names of variables or other objects, just as a
+symbolic link in a Unix filesystem contains merely the name of a file.
+The C<*glob> notation is something of a symbolic reference. (Symbolic
+references are sometimes called "soft references", but please don't call
+them that; references are confusing enough without useless synonyms.)
+X<reference, symbolic> X<reference, soft>
+X<symbolic reference> X<soft reference>
+
+In contrast, hard references are more like hard links in a Unix file
+system: They are used to access an underlying object without concern for
+what its (other) name is. When the word "reference" is used without an
+adjective, as in the following paragraph, it is usually talking about a
+hard reference.
+X<reference, hard> X<hard reference>
+
+References are easy to use in Perl. There is just one overriding
+principle: Perl does no implicit referencing or dereferencing. When a
+scalar is holding a reference, it always behaves as a simple scalar. It
+doesn't magically start being an array or hash or subroutine; you have to
+tell it explicitly to do so, by dereferencing it.
+
+=head2 Making References
+X<reference, creation> X<referencing>
+
+References can be created in several ways.
+
+=over 4
+
+=item 1.
+X<\> X<backslash>
+
+By using the backslash operator on a variable, subroutine, or value.
+(This works much like the & (address-of) operator in C.)
+This typically creates I<another> reference to a variable, because
+there's already a reference to the variable in the symbol table. But
+the symbol table reference might go away, and you'll still have the
+reference that the backslash returned. Here are some examples:
+
+ $scalarref = \$foo;
+ $arrayref = \@ARGV;
+ $hashref = \%ENV;
+ $coderef = \&handler;
+ $globref = \*foo;
+
+It isn't possible to create a true reference to an IO handle (filehandle
+or dirhandle) using the backslash operator. The most you can get is a
+reference to a typeglob, which is actually a complete symbol table entry.
+But see the explanation of the C<*foo{THING}> syntax below. However,
+you can still use type globs and globrefs as though they were IO handles.
+
+=item 2.
+X<array, anonymous> X<[> X<[]> X<square bracket>
+X<bracket, square> X<arrayref> X<array reference> X<reference, array>
+
+A reference to an anonymous array can be created using square
+brackets:
+
+ $arrayref = [1, 2, ['a', 'b', 'c']];
+
+Here we've created a reference to an anonymous array of three elements
+whose final element is itself a reference to another anonymous array of three
+elements. (The multidimensional syntax described later can be used to
+access this. For example, after the above, C<< $arrayref->[2][1] >> would have
+the value "b".)
+
+Taking a reference to an enumerated list is not the same
+as using square brackets--instead it's the same as creating
+a list of references!
+
+ @list = (\$a, \@b, \%c);
+ @list = \($a, @b, %c); # same thing!
+
+As a special case, C<\(@foo)> returns a list of references to the contents
+of C<@foo>, not a reference to C<@foo> itself. Likewise for C<%foo>,
+except that the key references are to copies (since the keys are just
+strings rather than full-fledged scalars).
+
+=item 3.
+X<hash, anonymous> X<{> X<{}> X<curly bracket>
+X<bracket, curly> X<brace> X<hashref> X<hash reference> X<reference, hash>
+
+A reference to an anonymous hash can be created using curly
+brackets:
+
+ $hashref = {
+ 'Adam' => 'Eve',
+ 'Clyde' => 'Bonnie',
+ };
+
+Anonymous hash and array composers like these can be intermixed freely to
+produce as complicated a structure as you want. The multidimensional
+syntax described below works for these too. The values above are
+literals, but variables and expressions would work just as well, because
+assignment operators in Perl (even within local() or my()) are executable
+statements, not compile-time declarations.
+
+Because curly brackets (braces) are used for several other things
+including BLOCKs, you may occasionally have to disambiguate braces at the
+beginning of a statement by putting a C<+> or a C<return> in front so
+that Perl realizes the opening brace isn't starting a BLOCK. The economy and
+mnemonic value of using curlies is deemed worth this occasional extra
+hassle.
+
+For example, if you wanted a function to make a new hash and return a
+reference to it, you have these options:
+
+ sub hashem { { @_ } } # silently wrong
+ sub hashem { +{ @_ } } # ok
+ sub hashem { return { @_ } } # ok
+
+On the other hand, if you want the other meaning, you can do this:
+
+ sub showem { { @_ } } # ambiguous (currently ok, but may change)
+ sub showem { {; @_ } } # ok
+ sub showem { { return @_ } } # ok
+
+The leading C<+{> and C<{;> always serve to disambiguate
+the expression to mean either the HASH reference, or the BLOCK.
+
+=item 4.
+X<subroutine, anonymous> X<subroutine, reference> X<reference, subroutine>
+X<scope, lexical> X<closure> X<lexical> X<lexical scope>
+
+A reference to an anonymous subroutine can be created by using
+C<sub> without a subname:
+
+ $coderef = sub { print "Boink!\n" };
+
+Note the semicolon. Except for the code
+inside not being immediately executed, a C<sub {}> is not so much a
+declaration as it is an operator, like C<do{}> or C<eval{}>. (However, no
+matter how many times you execute that particular line (unless you're in an
+C<eval("...")>), $coderef will still have a reference to the I<same>
+anonymous subroutine.)
+
+Anonymous subroutines act as closures with respect to my() variables,
+that is, variables lexically visible within the current scope. Closure
+is a notion out of the Lisp world that says if you define an anonymous
+function in a particular lexical context, it pretends to run in that
+context even when it's called outside the context.
+
+In human terms, it's a funny way of passing arguments to a subroutine when
+you define it as well as when you call it. It's useful for setting up
+little bits of code to run later, such as callbacks. You can even
+do object-oriented stuff with it, though Perl already provides a different
+mechanism to do that--see L<perlobj>.
+
+You might also think of closure as a way to write a subroutine
+template without using eval(). Here's a small example of how
+closures work:
+
+ sub newprint {
+ my $x = shift;
+ return sub { my $y = shift; print "$x, $y!\n"; };
+ }
+ $h = newprint("Howdy");
+ $g = newprint("Greetings");
+
+ # Time passes...
+
+ &$h("world");
+ &$g("earthlings");
+
+This prints
+
+ Howdy, world!
+ Greetings, earthlings!
+
+Note particularly that $x continues to refer to the value passed
+into newprint() I<despite> "my $x" having gone out of scope by the
+time the anonymous subroutine runs. That's what a closure is all
+about.
+
+This applies only to lexical variables, by the way. Dynamic variables
+continue to work as they have always worked. Closure is not something
+that most Perl programmers need trouble themselves about to begin with.
+
+=item 5.
+X<constructor> X<new>
+
+References are often returned by special subroutines called constructors. Perl
+objects are just references to a special type of object that happens to know
+which package it's associated with. Constructors are just special subroutines
+that know how to create that association. They do so by starting with an
+ordinary reference, and it remains an ordinary reference even while it's also
+being an object. Constructors are often named C<new()>. You I<can> call them
+indirectly:
+
+ $objref = new Doggie( Tail => 'short', Ears => 'long' );
+
+But that can produce ambiguous syntax in certain cases, so it's often
+better to use the direct method invocation approach:
+
+ $objref = Doggie->new(Tail => 'short', Ears => 'long');
+
+ use Term::Cap;
+ $terminal = Term::Cap->Tgetent( { OSPEED => 9600 });
+
+ use Tk;
+ $main = MainWindow->new();
+ $menubar = $main->Frame(-relief => "raised",
+ -borderwidth => 2)
+
+=item 6.
+X<autovivification>
+
+References of the appropriate type can spring into existence if you
+dereference them in a context that assumes they exist. Because we haven't
+talked about dereferencing yet, we can't show you any examples yet.
+
+=item 7.
+X<*foo{THING}> X<*>
+
+A reference can be created by using a special syntax, lovingly known as
+the *foo{THING} syntax. *foo{THING} returns a reference to the THING
+slot in *foo (which is the symbol table entry which holds everything
+known as foo).
+
+ $scalarref = *foo{SCALAR};
+ $arrayref = *ARGV{ARRAY};
+ $hashref = *ENV{HASH};
+ $coderef = *handler{CODE};
+ $ioref = *STDIN{IO};
+ $globref = *foo{GLOB};
+ $formatref = *foo{FORMAT};
+
+All of these are self-explanatory except for C<*foo{IO}>. It returns
+the IO handle, used for file handles (L<perlfunc/open>), sockets
+(L<perlfunc/socket> and L<perlfunc/socketpair>), and directory
+handles (L<perlfunc/opendir>). For compatibility with previous
+versions of Perl, C<*foo{FILEHANDLE}> is a synonym for C<*foo{IO}>, though it
+is deprecated as of 5.8.0. If deprecation warnings are in effect, it will warn
+of its use.
+
+C<*foo{THING}> returns undef if that particular THING hasn't been used yet,
+except in the case of scalars. C<*foo{SCALAR}> returns a reference to an
+anonymous scalar if $foo hasn't been used yet. This might change in a
+future release.
+
+C<*foo{IO}> is an alternative to the C<*HANDLE> mechanism given in
+L<perldata/"Typeglobs and Filehandles"> for passing filehandles
+into or out of subroutines, or storing into larger data structures.
+Its disadvantage is that it won't create a new filehandle for you.
+Its advantage is that you have less risk of clobbering more than
+you want to with a typeglob assignment. (It still conflates file
+and directory handles, though.) However, if you assign the incoming
+value to a scalar instead of a typeglob as we do in the examples
+below, there's no risk of that happening.
+
+ splutter(*STDOUT); # pass the whole glob
+ splutter(*STDOUT{IO}); # pass both file and dir handles
+
+ sub splutter {
+ my $fh = shift;
+ print $fh "her um well a hmmm\n";
+ }
+
+ $rec = get_rec(*STDIN); # pass the whole glob
+ $rec = get_rec(*STDIN{IO}); # pass both file and dir handles
+
+ sub get_rec {
+ my $fh = shift;
+ return scalar <$fh>;
+ }
+
+=back
+
+=head2 Using References
+X<reference, use> X<dereferencing> X<dereference>
+
+That's it for creating references. By now you're probably dying to
+know how to use references to get back to your long-lost data. There
+are several basic methods.
+
+=over 4
+
+=item 1.
+
+Anywhere you'd put an identifier (or chain of identifiers) as part
+of a variable or subroutine name, you can replace the identifier with
+a simple scalar variable containing a reference of the correct type:
+
+ $bar = $$scalarref;
+ push(@$arrayref, $filename);
+ $$arrayref[0] = "January";
+ $$hashref{"KEY"} = "VALUE";
+ &$coderef(1,2,3);
+ print $globref "output\n";
+
+It's important to understand that we are specifically I<not> dereferencing
+C<$arrayref[0]> or C<$hashref{"KEY"}> there. The dereference of the
+scalar variable happens I<before> it does any key lookups. Anything more
+complicated than a simple scalar variable must use methods 2 or 3 below.
+However, a "simple scalar" includes an identifier that itself uses method
+1 recursively. Therefore, the following prints "howdy".
+
+ $refrefref = \\\"howdy";
+ print $$$$refrefref;
+
+=item 2.
+
+Anywhere you'd put an identifier (or chain of identifiers) as part of a
+variable or subroutine name, you can replace the identifier with a
+BLOCK returning a reference of the correct type. In other words, the
+previous examples could be written like this:
+
+ $bar = ${$scalarref};
+ push(@{$arrayref}, $filename);
+ ${$arrayref}[0] = "January";
+ ${$hashref}{"KEY"} = "VALUE";
+ &{$coderef}(1,2,3);
+ $globref->print("output\n"); # iff IO::Handle is loaded
+
+Admittedly, it's a little silly to use the curlies in this case, but
+the BLOCK can contain any arbitrary expression, in particular,
+subscripted expressions:
+
+ &{ $dispatch{$index} }(1,2,3); # call correct routine
+
+Because of being able to omit the curlies for the simple case of C<$$x>,
+people often make the mistake of viewing the dereferencing symbols as
+proper operators, and wonder about their precedence. If they were,
+though, you could use parentheses instead of braces. That's not the case.
+Consider the difference below; case 0 is a short-hand version of case 1,
+I<not> case 2:
+
+ $$hashref{"KEY"} = "VALUE"; # CASE 0
+ ${$hashref}{"KEY"} = "VALUE"; # CASE 1
+ ${$hashref{"KEY"}} = "VALUE"; # CASE 2
+ ${$hashref->{"KEY"}} = "VALUE"; # CASE 3
+
+Case 2 is also deceptive in that you're accessing a variable
+called %hashref, not dereferencing through $hashref to the hash
+it's presumably referencing. That would be case 3.
+
+=item 3.
+
+Subroutine calls and lookups of individual array elements arise often
+enough that it gets cumbersome to use method 2. As a form of
+syntactic sugar, the examples for method 2 may be written:
+
+ $arrayref->[0] = "January"; # Array element
+ $hashref->{"KEY"} = "VALUE"; # Hash element
+ $coderef->(1,2,3); # Subroutine call
+
+The left side of the arrow can be any expression returning a reference,
+including a previous dereference. Note that C<$array[$x]> is I<not> the
+same thing as C<< $array->[$x] >> here:
+
+ $array[$x]->{"foo"}->[0] = "January";
+
+This is one of the cases we mentioned earlier in which references could
+spring into existence when in an lvalue context. Before this
+statement, C<$array[$x]> may have been undefined. If so, it's
+automatically defined with a hash reference so that we can look up
+C<{"foo"}> in it. Likewise C<< $array[$x]->{"foo"} >> will automatically get
+defined with an array reference so that we can look up C<[0]> in it.
+This process is called I<autovivification>.
+
+One more thing here. The arrow is optional I<between> brackets
+subscripts, so you can shrink the above down to
+
+ $array[$x]{"foo"}[0] = "January";
+
+Which, in the degenerate case of using only ordinary arrays, gives you
+multidimensional arrays just like C's:
+
+ $score[$x][$y][$z] += 42;
+
+Well, okay, not entirely like C's arrays, actually. C doesn't know how
+to grow its arrays on demand. Perl does.
+
+=item 4.
+
+If a reference happens to be a reference to an object, then there are
+probably methods to access the things referred to, and you should probably
+stick to those methods unless you're in the class package that defines the
+object's methods. In other words, be nice, and don't violate the object's
+encapsulation without a very good reason. Perl does not enforce
+encapsulation. We are not totalitarians here. We do expect some basic
+civility though.
+
+=back
+
+Using a string or number as a reference produces a symbolic reference,
+as explained above. Using a reference as a number produces an
+integer representing its storage location in memory. The only
+useful thing to be done with this is to compare two references
+numerically to see whether they refer to the same location.
+X<reference, numeric context>
+
+ if ($ref1 == $ref2) { # cheap numeric compare of references
+ print "refs 1 and 2 refer to the same thing\n";
+ }
+
+Using a reference as a string produces both its referent's type,
+including any package blessing as described in L<perlobj>, as well
+as the numeric address expressed in hex. The ref() operator returns
+just the type of thing the reference is pointing to, without the
+address. See L<perlfunc/ref> for details and examples of its use.
+X<reference, string context>
+
+The bless() operator may be used to associate the object a reference
+points to with a package functioning as an object class. See L<perlobj>.
+
+A typeglob may be dereferenced the same way a reference can, because
+the dereference syntax always indicates the type of reference desired.
+So C<${*foo}> and C<${\$foo}> both indicate the same scalar variable.
+
+Here's a trick for interpolating a subroutine call into a string:
+
+ print "My sub returned @{[mysub(1,2,3)]} that time.\n";
+
+The way it works is that when the C<@{...}> is seen in the double-quoted
+string, it's evaluated as a block. The block creates a reference to an
+anonymous array containing the results of the call to C<mysub(1,2,3)>. So
+the whole block returns a reference to an array, which is then
+dereferenced by C<@{...}> and stuck into the double-quoted string. This
+chicanery is also useful for arbitrary expressions:
+
+ print "That yields @{[$n + 5]} widgets\n";
+
+Similarly, an expression that returns a reference to a scalar can be
+dereferenced via C<${...}>. Thus, the above expression may be written
+as:
+
+ print "That yields ${\($n + 5)} widgets\n";
+
+=head2 Symbolic references
+X<reference, symbolic> X<reference, soft>
+X<symbolic reference> X<soft reference>
+
+We said that references spring into existence as necessary if they are
+undefined, but we didn't say what happens if a value used as a
+reference is already defined, but I<isn't> a hard reference. If you
+use it as a reference, it'll be treated as a symbolic
+reference. That is, the value of the scalar is taken to be the I<name>
+of a variable, rather than a direct link to a (possibly) anonymous
+value.
+
+People frequently expect it to work like this. So it does.
+
+ $name = "foo";
+ $$name = 1; # Sets $foo
+ ${$name} = 2; # Sets $foo
+ ${$name x 2} = 3; # Sets $foofoo
+ $name->[0] = 4; # Sets $foo[0]
+ @$name = (); # Clears @foo
+ &$name(); # Calls &foo() (as in Perl 4)
+ $pack = "THAT";
+ ${"${pack}::$name"} = 5; # Sets $THAT::foo without eval
+
+This is powerful, and slightly dangerous, in that it's possible
+to intend (with the utmost sincerity) to use a hard reference, and
+accidentally use a symbolic reference instead. To protect against
+that, you can say
+
+ use strict 'refs';
+
+and then only hard references will be allowed for the rest of the enclosing
+block. An inner block may countermand that with
+
+ no strict 'refs';
+
+Only package variables (globals, even if localized) are visible to
+symbolic references. Lexical variables (declared with my()) aren't in
+a symbol table, and thus are invisible to this mechanism. For example:
+
+ local $value = 10;
+ $ref = "value";
+ {
+ my $value = 20;
+ print $$ref;
+ }
+
+This will still print 10, not 20. Remember that local() affects package
+variables, which are all "global" to the package.
+
+=head2 Not-so-symbolic references
+
+A new feature contributing to readability in perl version 5.001 is that the
+brackets around a symbolic reference behave more like quotes, just as they
+always have within a string. That is,
+
+ $push = "pop on ";
+ print "${push}over";
+
+has always meant to print "pop on over", even though push is
+a reserved word. This has been generalized to work the same outside
+of quotes, so that
+
+ print ${push} . "over";
+
+and even
+
+ print ${ push } . "over";
+
+will have the same effect. (This would have been a syntax error in
+Perl 5.000, though Perl 4 allowed it in the spaceless form.) This
+construct is I<not> considered to be a symbolic reference when you're
+using strict refs:
+
+ use strict 'refs';
+ ${ bareword }; # Okay, means $bareword.
+ ${ "bareword" }; # Error, symbolic reference.
+
+Similarly, because of all the subscripting that is done using single
+words, we've applied the same rule to any bareword that is used for
+subscripting a hash. So now, instead of writing
+
+ $array{ "aaa" }{ "bbb" }{ "ccc" }
+
+you can write just
+
+ $array{ aaa }{ bbb }{ ccc }
+
+and not worry about whether the subscripts are reserved words. In the
+rare event that you do wish to do something like
+
+ $array{ shift }
+
+you can force interpretation as a reserved word by adding anything that
+makes it more than a bareword:
+
+ $array{ shift() }
+ $array{ +shift }
+ $array{ shift @_ }
+
+The C<use warnings> pragma or the B<-w> switch will warn you if it
+interprets a reserved word as a string.
+But it will no longer warn you about using lowercase words, because the
+string is effectively quoted.
+
+=head2 Pseudo-hashes: Using an array as a hash
+X<pseudo-hash> X<pseudo hash> X<pseudohash>
+
+Pseudo-hashes have been removed from Perl. The 'fields' pragma
+remains available.
+
+=head2 Function Templates
+X<scope, lexical> X<closure> X<lexical> X<lexical scope>
+X<subroutine, nested> X<sub, nested> X<subroutine, local> X<sub, local>
+
+As explained above, an anonymous function with access to the lexical
+variables visible when that function was compiled, creates a closure. It
+retains access to those variables even though it doesn't get run until
+later, such as in a signal handler or a Tk callback.
+
+Using a closure as a function template allows us to generate many functions
+that act similarly. Suppose you wanted functions named after the colors
+that generated HTML font changes for the various colors:
+
+ print "Be ", red("careful"), "with that ", green("light");
+
+The red() and green() functions would be similar. To create these,
+we'll assign a closure to a typeglob of the name of the function we're
+trying to build.
+
+ @colors = qw(red blue green yellow orange purple violet);
+ for my $name (@colors) {
+ no strict 'refs'; # allow symbol table manipulation
+ *$name = *{uc $name} = sub { "<FONT COLOR='$name'>@_</FONT>" };
+ }
+
+Now all those different functions appear to exist independently. You can
+call red(), RED(), blue(), BLUE(), green(), etc. This technique saves on
+both compile time and memory use, and is less error-prone as well, since
+syntax checks happen at compile time. It's critical that any variables in
+the anonymous subroutine be lexicals in order to create a proper closure.
+That's the reasons for the C<my> on the loop iteration variable.
+
+This is one of the only places where giving a prototype to a closure makes
+much sense. If you wanted to impose scalar context on the arguments of
+these functions (probably not a wise idea for this particular example),
+you could have written it this way instead:
+
+ *$name = sub ($) { "<FONT COLOR='$name'>$_[0]</FONT>" };
+
+However, since prototype checking happens at compile time, the assignment
+above happens too late to be of much use. You could address this by
+putting the whole loop of assignments within a BEGIN block, forcing it
+to occur during compilation.
+
+Access to lexicals that change over time--like those in the C<for> loop
+above, basically aliases to elements from the surrounding lexical scopes--
+only works with anonymous subs, not with named subroutines. Generally
+said, named subroutines do not nest properly and should only be declared
+in the main package scope.
+
+This is because named subroutines are created at compile time so their
+lexical variables get assigned to the parent lexicals from the first
+execution of the parent block. If a parent scope is entered a second
+time, its lexicals are created again, while the nested subs still
+reference the old ones.
+
+Anonymous subroutines get to capture each time you execute the C<sub>
+operator, as they are created on the fly. If you are accustomed to using
+nested subroutines in other programming languages with their own private
+variables, you'll have to work at it a bit in Perl. The intuitive coding
+of this type of thing incurs mysterious warnings about "will not stay
+shared" due to the reasons explained above.
+For example, this won't work:
+
+ sub outer {
+ my $x = $_[0] + 35;
+ sub inner { return $x * 19 } # WRONG
+ return $x + inner();
+ }
+
+A work-around is the following:
+
+ sub outer {
+ my $x = $_[0] + 35;
+ local *inner = sub { return $x * 19 };
+ return $x + inner();
+ }
+
+Now inner() can only be called from within outer(), because of the
+temporary assignments of the anonymous subroutine. But when it does,
+it has normal access to the lexical variable $x from the scope of
+outer() at the time outer is invoked.
+
+This has the interesting effect of creating a function local to another
+function, something not normally supported in Perl.
+
+=head1 WARNING
+X<reference, string context> X<reference, use as hash key>
+
+You may not (usefully) use a reference as the key to a hash. It will be
+converted into a string:
+
+ $x{ \$a } = $a;
+
+If you try to dereference the key, it won't do a hard dereference, and
+you won't accomplish what you're attempting. You might want to do something
+more like
+
+ $r = \@a;
+ $x{ $r } = $r;
+
+And then at least you can use the values(), which will be
+real refs, instead of the keys(), which won't.
+
+The standard Tie::RefHash module provides a convenient workaround to this.
+
+=head1 SEE ALSO
+
+Besides the obvious documents, source code can be instructive.
+Some pathological examples of the use of references can be found
+in the F<t/op/ref.t> regression test in the Perl source directory.
+
+See also L<perldsc> and L<perllol> for how to use references to create
+complex data structures, and L<perltoot>, L<perlobj>, and L<perlbot>
+for how to use them to create objects.