NAME
Lexical::Types - Extend the semantics of typed lexicals.
VERSION
Version 0.13
SYNOPSIS
{ package Str; }
{
package My::Types::Str;
sub new { bless { }, shift }
}
use Lexical::Types as => sub { 'My::Types::' . $_[0] => 'new' };
my Str $x; # $x is now a My::Types::Str object
{
package My::Types::Int;
sub TYPEDSCALAR { bless { }, shift }
}
use Lexical::Types;
use constant Int => 'My::Types::Int';
my Int $y; # $y is now a My::Types::Int object
DESCRIPTION
This pragma allows you to hook the execution of typed lexicals
declarations ("my Str $x") by calling a configurable method in a
configurable package at each run. In particular, it can be used to
automatically tie or bless typed lexicals whenever they are initialized.
Remind that for "perl" to be able to parse "my Str $x", you need :
* either the "Str" package to be defined ;
* or for "Str" to be a constant sub returning a valid defined package.
so make sure you follow one of those two strategies to define your
types.
This pragma is not implemented with a source filter.
METHODS
"import"
use Lexical::Types;
use Lexical::Types as => $prefix;
use Lexical::Types as => sub { ... }; # = $mangler
Magically called when "use Lexical::Types" is encountered. All the
occurences of "my Str $x" in the current lexical scope will be changed
to call at each run a given method in a given package. The method and
package are determined by the parameter 'as' :
* If it's left unspecified, the "TYPEDSCALAR" method in the "Str"
package will be called.
use Lexical::Types;
my Str $x; # calls Str->TYPEDSCALAR
* If a plain scalar $prefix is passed as the value, the "TYPEDSCALAR"
method in the "${prefix}::Str" package will be used.
use Lexical::Types as => 'My::'; # or "as => 'My'"
my Str $x; # calls My::Str->TYPEDSCALAR
* If the value given is a code reference $mangler, it will be called
at compile-time with arguments 'Str' and 'TYPEDSCALAR' and is
expected to return :
* either an empty list, in which case the current typed lexical
definition will be skipped (thus it won't be altered to trigger
a run-time hook) ;
use Lexical::Types as => sub {
return $_[0] =~ /Str/ ? @_ : ()
};
my Str $y; # calls Str->TYPEDSCALAR
my Int $x; # nothing special
* or the desired package and method name, in that order (if any of
those is "undef", the default value will be used instead).
use Lexical::Types as => sub { 'My', 'new_' . lc($_[0]) };
my Str $x; # the coderef indicates to call My->new_str
Note that if the type is a constant, $_[0] will be set to the
*value* of constant and not to its name.
use Lexical::Types as => sub { $_[0] => 'new' };
use constant Str => 'MyStr';
my Str $x; # calls MyStr->new
This means in particular that you can't both use constant types and
redirect several types to different methods of the same package,
because then you can't distinguish between the original types with
$_[0].
"unimport"
no Lexical::Types;
Magically called when "no Lexical::Types" is encountered. Turns the
pragma off.
RUN-TIME INITIALIZER METHOD
The initializer method receives an alias to the pad slot of the
initialized lexical in $_[1] and the original type name in $_[2]. You
can either edit $_[1] in place, in which case you should return an empty
list, or return a new scalar that will be copied into the pad slot.
use Lexical::Types as => 'My';
my Str $x;
...
sub My::Str::TYPEDSCALAR {
# $_[1] is an alias to $x, and $_[2] is 'Str'
...
}
INTEGRATION
You can integrate Lexical::Types in your module so that using it will
provide types to your users without asking them to load either
Lexical::Types or the type classes manually.
package MyTypes;
BEGIN { require Lexical::Types; }
sub import {
eval 'package Str; package Int'; # The types you want to support
Lexical::Types->import(
as => sub { __PACKAGE__, 'new_' . lc($_[0]) }
);
}
sub unimport {
Lexical::Types->unimport;
}
sub new_str { ... }
sub new_int { ... }
If you prefer to use constants rather than creating empty packages, you
can replace the previous example with something like this :
package MyTypes;
BEGIN { require Lexical::Types; }
sub import {
my $pkg = caller;
for (qw<Str Int>) {
my $type = __PACKAGE__ . '::' . $_;
no strict 'refs';
no warnings 'redefine';
*{$pkg.'::'.$_} = eval "sub () { '$type' }";
}
Lexical::Types->import(
as => sub { $_[0] => 'new' }
);
}
sub unimport {
Lexical::Types->unimport;
}
package MyTypes::Str;
sub new { ... }
package MyTypes::Int;
sub new { ... }
CONSTANTS
"LT_THREADSAFE"
True iff the module could have been built with thread-safety features
enabled.
"LT_FORKSAFE"
True iff this module could have been built with fork-safety features
enabled. This will always be true except on Windows where it's false for
perl 5.10.0 and below .
CAVEATS
Using this pragma will cause a slight global slowdown of any subsequent
compilation phase that happens anywere in your code - even outside of
the scope of use of "use Lexical::Types" - which may become noticeable
if you rely heavily on numerous calls to "eval STRING".
The restrictions on the type (being either a defined package name or a
constant) apply even if you use the 'as' option to redirect to another
package, and are unlikely to find a workaround as this happens deep
inside the lexer - far from the reach of an extension.
Only one mangler or prefix can be in use at the same time in a given
scope.
Typed lexicals declarations that appear in code "eval"'d during the
global destruction phase of a spawned thread or pseudo-fork (the
processes used internally for the "fork" emulation on Windows) are
ignored.
The implementation was tweaked to work around several limitations of
vanilla "perl" pragmas : it's thread safe, and doesn't suffer from a
"perl 5.8.x-5.10.0" bug that causes all pragmas to propagate into
"require"d scopes.
With 5.8 perls, the pragma does not propagate into "eval STRING". This
is due to a shortcoming in the way perl handles the hints hash, which is
addressed in perl 5.10.
DEPENDENCIES
perl 5.8.3.
A C compiler. This module may happen to build with a C++ compiler as
well, but don't rely on it, as no guarantee is made in this regard.
XSLoader (standard since perl 5.6.0).
SEE ALSO
fields.
Attribute::Handlers.
AUTHOR
Vincent Pit, "<perl at profvince.com>", <http://www.profvince.com>.
You can contact me by mail or on "irc.perl.org" (vincent).
BUGS
Please report any bugs or feature requests to "bug-lexical-types at
rt.cpan.org", or through the web interface at
<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Lexical-Types>. I will
be notified, and then you'll automatically be notified of progress on
your bug as I make changes.
SUPPORT
You can find documentation for this module with the perldoc command.
perldoc Lexical::Types
Tests code coverage report is available at
<http://www.profvince.com/perl/cover/Lexical-Types>.
ACKNOWLEDGEMENTS
Inspired by Ricardo Signes.
Thanks Florian Ragwitz for suggesting the use of constants for types.
COPYRIGHT & LICENSE
Copyright 2009,2010,2011,2012,2013,2014 Vincent Pit, all rights
reserved.
This program is free software; you can redistribute it and/or modify it
under the same terms as Perl itself.