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Sample Perl lexical pragma
#!/usr/bin/env perl
use 5.010;
use strict;
use warnings;
package Noise;
BEGIN {
# This trick prevents 'use Noise ...' from trying to find and load
# Noise.pm.
$INC{'Noise.pm'} = $0;
}
# The convention for naming %^H keys is "name-space/key-name".
use constant NOISE => join '/', __PACKAGE__, 'noise';
# This gets called implicitly by 'use Noise ...'
sub import {
$^H{ +NOISE } = $_[1]; # $_[0] is the package name.
return;
}
sub noise {
my $hints_hash = ( caller 0 )[10];
return $hints_hash->{ +NOISE };
}
sub call_import {
my ( $invocant, @args ) = @_;
return $invocant->import( @args );
}
package main;
use Noise 'The dog barks';
say Noise->noise(); # The dog barks
{
use Noise 'The cat meows';
say Noise->noise(); # The cat meows
}
# The previous value is restored on scope exit
say Noise->noise(); # The dog barks
BEGIN {
Noise->import( 'The cow moos' );
}
# A BEGIN block is good enough. No magic specific to 'use'
say Noise->noise(); # The cow moos
BEGIN {
{
Noise->call_import( 'The giraffe says nothing' );
}
}
# Scopes, or even call frames, in a BEGIN do not matter when setting %^H
say Noise->noise(); # The giraffe says nothing
# ex: set textwidth=72 :
@matthewpersico
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matthewpersico commented Dec 31, 2021

# ex: set textwidth=72 :

That's just fantastic!

@matthewpersico
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matthewpersico commented Dec 31, 2021

So THAT'S how that works! I've been Perling since 1997 and yet I still manage to find out new things. Thank you.

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