one large indistinguishable list.
If no C<return> is found and if the last statement is an expression, its
-value is returned. Otherwise, if the last statement is a control structure
-like a C<foreach>, the returned value is unspecified. The empty sub
-returns the empty list.
+value is returned. If the last statement is a loop control structure
+like a C<foreach> or a C<while>, the returned value is unspecified. The
+empty sub returns the empty list.
X<subroutine, return value> X<return value> X<return>
Perl does not have named formal parameters. In practice all you
Subroutines that do special, pre-defined things include C<AUTOLOAD>, C<CLONE>,
C<DESTROY> plus all functions mentioned in L<perltie> and L<PerlIO::via>.
-The C<BEGIN>, C<CHECK>, C<INIT> and C<END> subroutines are not so much
-subroutines as named special code blocks, of which you can have more
-than one in a package, and which you can B<not> call explicitly. See
-L<perlmod/"BEGIN, CHECK, INIT and END">
+The C<BEGIN>, C<UNITCHECK>, C<CHECK>, C<INIT> and C<END> subroutines
+are not so much subroutines as named special code blocks, of which you
+can have more than one in a package, and which you can B<not> call
+explicitly. See L<perlmod/"BEGIN, UNITCHECK, CHECK, INIT and END">
=head2 Private Variables via my()
X<my> X<variable, lexical> X<lexical> X<lexical variable> X<scope, lexical>
allowed to try to make a package variable (or other global) lexical:
my $pack::var; # ERROR! Illegal syntax
- my $_; # also illegal (currently)
In fact, a dynamic variable (also known as package or global variables)
are still accessible using the fully qualified C<::> notation even while a
this.
=head2 Persistent Private Variables
-X<static> X<variable, persistent> X<variable, static> X<closure>
+X<state> X<state variable> X<static> X<variable, persistent> X<variable, static> X<closure>
+
+There are two ways to build persistent private variables in Perl 5.10.
+First, you can simply use the C<state> feature. Or, you can use closures,
+if you want to stay compatible with releases older than 5.10.
+
+=head3 Persistent variables via state()
+
+Beginning with perl 5.9.4, you can declare variables with the C<state>
+keyword in place of C<my>. For that to work, though, you must have
+enabled that feature beforehand, either by using the C<feature> pragma, or
+by using C<-E> on one-liners. (see L<feature>)
+
+For example, the following code maintains a private counter, incremented
+each time the gimme_another() function is called:
+
+ use feature 'state';
+ sub gimme_another { state $x; return ++$x }
+
+Also, since C<$x> is lexical, it can't be reached or modified by any Perl
+code outside.
+
+Be aware that assignment to C<state> variables (as in C<state $x = 42>)
+are executed every time; to initialize (or re-initialize) an undefined
+state scalar, you can use, for example, the defined-or assignment :
+
+ state $x //= initial_value();
+
+=head3 Persistent variables with closures
Just because a lexical variable is lexically (also called statically)
scoped to its enclosing block, C<eval>, or C<do> FILE, this doesn't mean that
}
}
-See L<perlmod/"BEGIN, CHECK, INIT and END"> about the
-special triggered code blocks, C<BEGIN>, C<CHECK>, C<INIT> and C<END>.
+See L<perlmod/"BEGIN, UNITCHECK, CHECK, INIT and END"> about the
+special triggered code blocks, C<BEGIN>, C<UNITCHECK>, C<CHECK>,
+C<INIT> and C<END>.
If declared at the outermost scope (the file scope), then lexicals
work somewhat like C's file statics. They are available to all
sub myopen (*;$) myopen HANDLE, $name
sub mypipe (**) mypipe READHANDLE, WRITEHANDLE
sub mygrep (&@) mygrep { /foo/ } $a, $b, $c
- sub myrand ($) myrand 42
+ sub myrand (;$) myrand 42
sub mytime () mytime
Any backslashed prototype character represents an actual argument
...
}
-A semicolon separates mandatory arguments from optional arguments.
+A semicolon (C<;>) separates mandatory arguments from optional arguments.
It is redundant before C<@> or C<%>, which gobble up everything else.
+As the last character of a prototype, or just before a semicolon, you can
+use C<_> in place of C<$>: if this argument is not provided, C<$_> will be
+used instead.
+
Note how the last three examples in the table above are treated
specially by the parser. C<mygrep()> is parsed as a true list
operator, C<myrand()> is parsed as a true unary operator with unary
C<glob>, the C<< <*> >> glob operator is overridden as well.
In a similar fashion, overriding the C<readline> function also overrides
-the equivalent I/O operator C<< <FILEHANDLE> >>.
+the equivalent I/O operator C<< <FILEHANDLE> >>. Also, overriding
+C<readpipe> also overrides the operators C<``> and C<qx//>.
Finally, some built-ins (e.g. C<exists> or C<grep>) can't be overridden.
Examples of valid syntax (even though the attributes are unknown):
- sub fnord (&\%) : switch(10,foo(7,3)) : expensive ;
- sub plugh () : Ugly('\(") :Bad ;
+ sub fnord (&\%) : switch(10,foo(7,3)) : expensive;
+ sub plugh () : Ugly('\(") :Bad;
sub xyzzy : _5x5 { ... }
Examples of invalid syntax:
- sub fnord : switch(10,foo() ; # ()-string not balanced
- sub snoid : Ugly('(') ; # ()-string not balanced
- sub xyzzy : 5x5 ; # "5x5" not a valid identifier
- sub plugh : Y2::north ; # "Y2::north" not a simple identifier
- sub snurt : foo + bar ; # "+" not a colon or space
+ sub fnord : switch(10,foo(); # ()-string not balanced
+ sub snoid : Ugly('('); # ()-string not balanced
+ sub xyzzy : 5x5; # "5x5" not a valid identifier
+ sub plugh : Y2::north; # "Y2::north" not a simple identifier
+ sub snurt : foo + bar; # "+" not a colon or space
The attribute list is passed as a list of constant strings to the code
which associates them with the subroutine. In particular, the second example
https://perl5.git.perl.org / perl5.git / blobdiff