NAME
lexical::underscore - access your caller's lexical underscore
SYNOPSIS
use 5.010;
use lexical::underscore;
use Test::More;
sub is_uppercase {
my $var = @_ ? shift : ${lexical::underscore()};
return $var eq uc($var);
}
my $thing = 'FOO';
my $works = 0;
given ( $thing ) {
when ( is_uppercase ) { $works++ }
}
ok($works);
done_testing();
DESCRIPTION
Starting with Perl 5.10, it is possible to create a lexical version of the
Perl default variable $_. Certain Perl constructs like the `given` keyword
automatically use a lexical $_ rather than the global $_.
It is occasionallly useful for a sub to be able to access its caller's $_
variable regardless of whether it was lexical or not. The `(_)` sub
prototype is the official way to do so, however there are sometimes
disadvantages to this; in particular it can only appear as the final
required argument in a prototype, and there is no way of the sub
differentiating between an explicitly passed argument and $_.
This caused me problems with Scalar::Does, because I wanted to enable the
`does` function to be called as either:
does($thing, $role);
does($role); # assumes $thing = $_
With `_` in the prototype, $_ was passed to the function at the end of its
argument list; effectively `does($role, $thing)`, making it impossible to
tell which argument was the role.
Enter `lexical::underscore` which allows you to access your caller's
lexical $_ variable as easily as:
${lexical::underscore()}
You can access lexical $_ further up the call stack using:
${lexical::underscore($level)}
If you happen to ask for $_ at a level where no lexical $_ is available,
you get the global $_ instead.
This module does work on Perl 5.8 but as there is no lexical $_, always
returns the global $_.
Technical Details
The `lexical::underscore` function returns a scalar reference to either a
lexical $_ variable somewhere up the call stack (using PadWalker magic),
or to the global $_ if there was no lexical version.
Wrapping `lexical::underscore` in `${ ... }` dereferences the scalar
reference, allowing you to access (and even assign to) it.
BUGS
Please report any bugs to
<http://rt.cpan.org/Dist/Display.html?Queue=lexical-underscore>.
SEE ALSO
PadWalker.
AUTHOR
Toby Inkster <tobyink@cpan.org>.
COPYRIGHT AND LICENCE
This software is copyright (c) 2012, 2014 by Toby Inkster.
This is free software; you can redistribute it and/or modify it under the
same terms as the Perl 5 programming language system itself.
DISCLAIMER OF WARRANTIES
THIS PACKAGE IS PROVIDED "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.