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# You may distribute under the terms of either the GNU General Public License |
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# or the Artistic License (the same terms as Perl itself) |
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# |
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# (C) Paul Evans, 2023 -- leonerd@leonerd.org.uk |
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package Signature::Attribute::Alias 0.01; |
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use v5.14; |
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use warnings; |
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require XSLoader; |
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XSLoader::load( __PACKAGE__, our $VERSION ); |
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=head1 NAME |
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C - make signature parameters that alias caller-provided values |
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=head1 SYNOPSIS |
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use v5.26; |
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use Sublike::Extended; |
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use Signature::Attribute::Alias; |
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use experimental 'signatures'; |
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extended sub trim_spaces ($s :Alias) { |
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$s =~ s/^\s+//; |
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$s =~ s/\s+$//; |
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} |
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my $string = " hello, world! "; |
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trim_spaces $string; |
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say "<$string>"; |
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=head1 DESCRIPTION |
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This module provides a third-party subroutine parameter attribute via |
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L, which declares that the parameter will alias the value |
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passed by the caller, rather than take a copy of it. |
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B The ability for sublike constructions to take third-party parameter |
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attributes is still new and highly experimental, and subject to much API |
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change in future. As a result, this module should be considered equally |
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experimental. Core perl's parser does not permit parameters to take |
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attributes. This ability must be requested specially; either by using |
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L, or perhaps enabled directly by some other sublike |
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keyword using the C infrastructure. |
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=head1 PARAMETER ATTRIBUTES |
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=head2 :Alias |
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extended sub f($x :Alias) { ... } |
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Declares that the lexical variable created by the parameter will be an alias |
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to the value passed in by the caller rather than, as would normally be the |
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case, simply contain a copy it. This means that any modifications of the |
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lexical within the subroutine will be reflected in the value from the caller - |
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which, therefore - must be mutable. |
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It is not automatically an error if the caller passes in an immutable value |
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(such as a constant), but any attempt to modify it will yield the usual |
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"Modification of read-only value attempted ..." warning from within the body |
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of the subroutine. |
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This attribute can only be applied to positional, scalar parameters that are |
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mandatory; i.e. do not have a defaulting expression. |
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=cut |
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sub import |
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{ |
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$^H{"Signature::Attribute::Alias/Alias"}++; |
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} |
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sub unimport |
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{ |
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delete $^H{"Signature::Attribute::Alias/Alias"}; |
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} |
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=head1 AUTHOR |
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Paul Evans |
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=cut |
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0x55AA; |