/ 
Devel-Pragma-0.32
River stage one • 2 direct dependents • 7 total dependents
/ Devel::Pragma

NAME

Devel::Pragma - helper functions for developers of lexical pragmas

SYNOPSIS

package MyPragma;

use Devel::Pragma qw(my_hints ccstash new_scope);

sub import {
    my ($class, %options) = @_;
    my $hints = my_hints;   # lexically-scoped %^H
    my $caller = ccstash(); # currently-compiling stash

    $hints->{MyPragma} = 1;

    if (new_scope($class)) {
        ...
    }

    my $scope_id = scope();
}

DESCRIPTION

This module provides helper functions for developers of lexical pragmas. These can be used both in older versions of perl (from 5.8.0), which have limited support for lexical pragmas, and in the most recent versions, which have improved support.

EXPORTS

Devel::Pragma exports the following functions on demand. They can all be imported at once by using the :all tag. e.g.

use Devel::Pragma qw(:all);

my_hints

Until perl change #33311, which isn't currently available in any stable perl release, values set in %^H are visible in files compiled by use, require and do FILE. This makes pragmas leak from the scope in which they're meant to be enabled into scopes in which they're not. my_hints fixes that by making %^H lexically scoped i.e. it prevents %^H leaking across file boundaries.

my_hints installs versions of perl's require and do FILE builtins in the currently-compiling scope which clear %^H before they execute and restore its values afterwards. Thus it can be thought of a lexically-scoped backport of change #33311.

Note that my_hints also sets the $^H bit that "localizes" (or in this case "lexicalizes") %^H.

The return value is a reference to %^H.

new_scope

This function returns true if the currently-compiling scope differs from the scope being compiled the last time new_scope was called. Subsequent calls will return false while the same scope is being compiled.

new_scope takes an optional parameter that is used to uniquely identify its caller. This should usually be supplied as the pragma's class name unless new_scope is called by a module that is not intended to be subclassed. e.g.

package MyPragma;

sub import {
    my ($class, %options) = @_;

    if (new_scope($class)) {
        ...
    }
}

If not supplied, the identifier defaults to the name of the calling package.

scope

This returns an integer that uniquely identifies the currently-compiling scope. It can be used to distinguish or compare scopes.

A warning is issued if scope (or new_scope) is called in a context in which it doesn't make sense i.e. if the scoped behaviour of %^H has not been enabled - either by explcitly modifying $^H, or by calling use Devel::Pragma or my_hints.

ccstash

This returns the name of the currently-compiling stash. It can be used as a replacement for the scalar form of caller to provide the name of the package in which use MyPragma is called. Unlike caller it returns the same value regardless of the number of intervening calls before MyPragma::import is reached.

e.g. given a pragma:

package MySuperPragma;

use Devel::Hints qw(ccstash);

sub import {
    my ($class, %options) = @_;
    my $caller = ccstash();

    no strict 'refs';

    *{"$caller\::whatever"} = ... ;
}

and a subclass:

package MySubPragma

use base qw(MySuperPragma);

sub import {
    my ($class, %options) = @_;
    $class->SUPER::import(...);
}

and a script that uses the subclass:

#!/usr/bin/env perl

use MySubPragma;

- the ccstash call in MySuperPragma::import returns the name of the package that's being compiled when the call to MySuperPragma::import (via MySubPragma::import) takes place i.e. main in this case.

VERSION

0.32

SEE ALSO

AUTHOR

chocolateboy <chocolate.boy@email.com>

COPYRIGHT AND LICENSE

Copyright (C) 2008-2009 by chocolateboy

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.8.8 or, at your option, any later version of Perl 5 you may have available.