/ 
Exporter-ConditionalSubs-v1.11.1
River stage one • 1 direct dependent • 2 total dependents
/ Exporter::ConditionalSubs

NAME

Exporter::ConditionalSubs - Conditionally export subroutines

VERSION

version v1.11.1

SYNOPSIS

Allows subroutines to be conditionally exported. If the condition is satisfied, the subroutine will be exported as usual. But if not, the subroutine will be replaced with a stub that gets optimized away by the compiler. When stubbed out, not even the arguments to the subroutine will get evaluated.

This allows for e.g. assertion-like behavior, where subroutine calls can be left in the code but effectively ignored under certain conditions.

First create a module that ISA Exporter::ConditionalSubs:

package My::Assertions;

require Exporter::ConditionalSubs;
our @ISA = qw( Exporter::ConditionalSubs );

our @EXPORT    = ();
our @EXPORT_OK = qw( _assert_non_empty );

sub _assert_non_empty
{
    carp "Found empty value" unless length(shift // '') > 0;
}

Then, specify an -if or -unless condition when useing that module:

package My::App;

use My::Assertions qw( _assert_non_empty ), -if => $ENV{DEBUG};

use My::MoreAssertions -unless => $ENV{RUNTIME} eq 'prod';

# Coderefs work too:
use My::OtherAssertions -if => sub { ... some logic ... };

_assert_non_empty($foo);    # this subroutine call might be a no-op

This is a subclass of Exporter and works just like it, with the addition of support for the -if and -unless import arguments.

SUBROUTINES

import

Works like the Exporter import() function, except that it checks for an optional -if or -unless import arg, followed by either a boolean, or a coderef that returns true/false.

If the condition evaluates to true for -if, or false for -unless, then any subs are exported as-is. Otherwise, any subs in @EXPORT_OK are replaced with stubs that get optimized away by the compiler (with one exception - see "CAVEATS" below).

You can specify either -if or -unless, but not both. Croaks if both are specified, or if you specify the same option more than once.

CAVEATS

This module uses B::CallChecker and B::Generate under the covers to optimize away the exported subroutines. Loading one or the other of those modules can potentially break test coverage metrics generated by Devel::Cover in mysterious ways.

To avoid this problem, subroutines are never optimized away if Devel::Cover is in use, and are always exported as-is regardless of any -if or -unless conditions. (You probably want Devel::Cover to assess the coverage of your real exported subroutines in any case.)

SEE ALSO

Exporter

B::CallChecker

B::Generate

ACKNOWLEDGEMENTS

Thanks to Grant Street Group http://www.grantstreet.com for funding development of this code.

Thanks to Tom Christiansen (<tchrist@perl.com>) for help with the symbol table hackery and Larry Leszczynski, <larryl at cpan.org> for writing most of the code.

Thanks to Zefram (<zefram@fysh.org>) for the pointer to his Debug::Show hackery.

AUTHOR

Grant Street Group <developers@grantstreet.com>

COPYRIGHT AND LICENSE

This software is Copyright (c) 2015 - 2020 by Grant Street Group.

This is free software, licensed under:

The Artistic License 2.0 (GPL Compatible)