=head1 DESCRIPTION
+=head2 Is this the document you were after?
+
+There are other documents which might contain the information that you're
+looking for:
+
+=over 2
+
+=item This doc
+
+Perl's packages, namespaces, and some info on classes.
+
+=item L<perlnewmod>
+
+Tutorial on making a new module.
+
+=item L<perlmodstyle>
+
+Best practices for making a new module.
+
+=back
+
=head2 Packages
X<package> X<namespace> X<variable, global> X<global variable> X<global>
-Perl provides a mechanism for alternative namespaces to protect
-packages from stomping on each other's variables. In fact, there's
-really no such thing as a global variable in Perl. The package
-statement declares the compilation unit as being in the given
-namespace. The scope of the package declaration is from the
+Unlike Perl 4, in which all the variables were dynamic and shared one
+global name space, causing maintainability problems, Perl 5 provides two
+mechanisms for protecting code from having its variables stomped on by
+other code: lexically scoped variables created with C<my> or C<state> and
+namespaced global variables, which are exposed via the C<vars> pragma,
+or the C<our> keyword. Any global variable is considered to
+be part of a namespace and can be accessed via a "fully qualified form".
+Conversely, any lexically scoped variable is considered to be part of
+that lexical-scope, and does not have a "fully qualified form".
+
+In perl namespaces are called "packages" and
+the C<package> declaration tells the compiler which
+namespace to prefix to C<our> variables and unqualified dynamic names.
+This both protects
+against accidental stomping and provides an interface for deliberately
+clobbering global dynamic variables declared and used in other scopes or
+packages, when that is what you want to do.
+
+The scope of the C<package> declaration is from the
declaration itself through the end of the enclosing block, C<eval>,
-or file, whichever comes first (the same scope as the my() and
-local() operators). Unqualified dynamic identifiers will be in
-this namespace, except for those few identifiers that if unqualified,
+or file, whichever comes first (the same scope as the my(), our(), state(), and
+local() operators, and also the effect
+of the experimental "reference aliasing," which may change), or until
+the next C<package> declaration. Unqualified dynamic identifiers will be in
+this namespace, except for those few identifiers that, if unqualified,
default to the main package instead of the current one as described
-below. A package statement affects only dynamic variables--including
-those you've used local() on--but I<not> lexical variables created
-with my(). Typically it would be the first declaration in a file
-included by the C<do>, C<require>, or C<use> operators. You can
-switch into a package in more than one place; it merely influences
-which symbol table is used by the compiler for the rest of that
-block. You can refer to variables and filehandles in other packages
+below. A C<package> statement affects only dynamic global
+symbols, including subroutine names, and variables you've used local()
+on, but I<not> lexical variables created with my(), our() or state().
+
+Typically, a C<package> statement is the first declaration in a file
+included in a program by one of the C<do>, C<require>, or C<use> operators. You can
+switch into a package in more than one place: C<package> has no
+effect beyond specifying which symbol table the compiler will use for
+dynamic symbols for the rest of that block or until the next C<package> statement.
+You can refer to variables and filehandles in other packages
by prefixing the identifier with the package name and a double
colon: C<$Package::Variable>. If the package name is null, the
C<main> package is assumed. That is, C<$::sail> is equivalent to
from the outer package name down. For instance, there is nowhere
within package C<OUTER> that C<$INNER::var> refers to
C<$OUTER::INNER::var>. C<INNER> refers to a totally
-separate global package.
+separate global package. The custom of treating package names as a
+hierarchy is very strong, but the language in no way enforces it.
Only identifiers starting with letters (or underscore) are stored
in a package's symbol table. All other symbols are kept in package
from). See L<perldebug>.
The special symbol C<__PACKAGE__> contains the current package, but cannot
-(easily) be used to construct variable names.
+(easily) be used to construct variable names. After C<my($foo)> has hidden
+package variable C<$foo>, it can still be accessed, without knowing what
+package you are in, as C<${__PACKAGE__.'::foo'}>.
See L<perlsub> for other scoping issues related to my() and local(),
and L<perlref> regarding closures.
instance. The standard but antiquated F<dumpvar.pl> library and
the CPAN module Devel::Symdump make use of this.
+The results of creating new symbol table entries directly or modifying any
+entries that are not already typeglobs are undefined and subject to change
+between releases of perl.
+
Assignment to a typeglob performs an aliasing operation, i.e.,
*dick = *richard;
sub identify_typeglob {
my $glob = shift;
- print 'You gave me ', *{$glob}{PACKAGE}, '::', *{$glob}{NAME}, "\n";
+ print 'You gave me ', *{$glob}{PACKAGE},
+ '::', *{$glob}{NAME}, "\n";
}
identify_typeglob *foo;
identify_typeglob *bar::baz;
C<UNITCHECK> blocks are run just after the unit which defined them has
been compiled. The main program file and each module it loads are
-compilation units, as are string C<eval>s, code compiled using the
+compilation units, as are string C<eval>s, run-time code compiled using the
C<(?{ })> construct in a regex, calls to C<do FILE>, C<require FILE>,
and code after the C<-e> switch on the command line.
}
INIT { print " 9. You'll see the difference right away.\n" }
- print "13. It merely _looks_ like it should be confusing.\n";
+ print "13. It only _looks_ like it should be confusing.\n";
__END__
by listing the other package name(s) in its global @ISA array (which
must be a package global, not a lexical).
-For more on this, see L<perl
toot> and L<perlobj>.
+For more on this, see L<perl
ootut> and L<perlobj>.
=head2 Perl Modules
X<module>
use strict;
use warnings;
- BEGIN {
- use Exporter ();
- our ($VERSION, @ISA, @EXPORT, @EXPORT_OK, %EXPORT_TAGS);
+ # Get the import method from Exporter to export functions and
+ # variables
+ use Exporter 5.57 'import';
- # set the version for version checking
- $VERSION = 1.00;
- # if using RCS/CVS, this may be preferred
- $VERSION = sprintf "%d.%03d", q$Revision: 1.1 $ =~ /(\d+)/g;
+ # set the version for version checking
+ our $VERSION = '1.00';
- @ISA = qw(Exporter);
- @EXPORT = qw(&func1 &func2 &func4);
- %EXPORT_TAGS = ( ); # eg: TAG => [ qw!name1 name2! ],
+ # Functions and variables which are exported by default
+ our @EXPORT = qw(func1 func2);
- # your exported package globals go here,
- # as well as any optionally exported functions
- @EXPORT_OK = qw($Var1 %Hashit &func3);
- }
- our @EXPORT_OK;
+ # Functions and variables which can be optionally exported
+ our @EXPORT_OK = qw($Var1 %Hashit func3);
# exported package globals go here
- our $Var1;
- our %Hashit;
+ our $Var1 = '';
+ our %Hashit = ();
# non-exported package globals go here
- our @more;
- our $stuff;
+ # (they are still accessible as $Some::Module::stuff)
+ our @more = ();
+ our $stuff = '';
- # initialize package globals, first exported ones
- $Var1 = '';
- %Hashit = ();
-
- # then the others (which are still accessible as $Some::Module::stuff)
- $stuff = '';
- @more = ();
-
- # all file-scoped lexicals must be created before
- # the functions below that use them.
-
- # file-private lexicals go here
+ # file-private lexicals go here, before any functions which use them
my $priv_var = '';
my %secret_hash = ();
# here's a file-private function as a closure,
- # callable as &$priv_func; it cannot be prototyped.
+ # callable as $priv_func->();
my $priv_func = sub {
- # stuff goes here.
+ ...
};
# make all your functions, whether exported or not;
# remember to put something interesting in the {} stubs
- sub func1 {} # no prototype
- sub func2() {} # proto'd void
- sub func3($$) {} # proto'd to 2 scalars
-
- # this one isn't exported, but could be called!
- sub func4(\%) {} # proto'd to 1 hash ref
+ sub func1 { ... }
+ sub func2 { ... }
- END { } # module clean-up code here (global destructor)
+ # this one isn't always exported, but could be called directly
+ # as Some::Module::func3()
+ sub func3 { ... }
- ## YOUR CODE GOES HERE
+ END { ... } # module clean-up code here (global destructor)
1; # don't forget to return a true value from the file
This is exactly equivalent to
- BEGIN { require Module; import Module; }
+ BEGIN { require 'Module.pm'; 'Module'->import; }
or
- BEGIN { require Module; import Module LIST; }
+ BEGIN { require 'Module.pm'; 'Module'->import( LIST ); }
As a special case
is exactly equivalent to
- BEGIN { require Module; }
+ BEGIN { require 'Module.pm'; }
All Perl module files have the extension F<.pm>. The C<use> operator
assumes this so you don't have to spell out "F<Module.pm>" in quotes.
X<module, threadsafe> X<module, thread safe>
X<CLONE> X<CLONE_SKIP> X<thread> X<threads> X<ithread>
-Since 5.6.0, Perl has had support for a new type of threads called
-interpreter threads (ithreads). These threads can be used explicitly
-and implicitly.
+Perl supports a type of threads called interpreter threads (ithreads).
+These threads can be used explicitly and implicitly.
Ithreads work by cloning the data tree so that no data is shared
between different threads. These threads can be used by using the C<threads>
module or by doing fork() on win32 (fake fork() support). When a
thread is cloned all Perl data is cloned, however non-Perl data cannot
-be cloned automatically. Perl after 5.7.2 has support for the C<CLONE>
+be cloned automatically. Perl after 5.8.0 has support for the C<CLONE>
special subroutine. In C<CLONE> you can do whatever
you need to do,
like for example handle the cloning of non-Perl data, if necessary.
C<CLONE> will be called once as a class method for every package that has it
defined (or inherits it). It will be called in the context of the new thread,
so all modifications are made in the new area. Currently CLONE is called with
-no parameters other than the invocand package name, but code should not assume
+no parameters other than the invocant package name, but code should not assume
that this will remain unchanged, as it is likely that in future extra parameters
will be passed in to give more information about the state of cloning.
needed.
Like C<CLONE>, C<CLONE_SKIP> is currently called with no parameters other
-than the invocand package name, although that may change. Similarly, to
+than the invocant package name, although that may change. Similarly, to
allow for future expansion, the return value should be a single C<0> or
C<1> value.
See L<perlmodlib> for general style issues related to building Perl
modules and classes, as well as descriptions of the standard library
and CPAN, L<Exporter> for how Perl's standard import/export mechanism
-works, L<perltoot> and L<perltooc> for an in-depth tutorial on
+works, L<perlootut> and L<perlobj> for in-depth information on
creating classes, L<perlobj> for a hard-core reference document on
objects, L<perlsub> for an explanation of functions and scoping,
and L<perlxstut> and L<perlguts> for more information on writing
https://perl5.git.perl.org / perl5.git / blobdiff