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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, 2018-2020 -- leonerd@leonerd.org.uk |
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package Syntax::Keyword::Dynamically 0.11; |
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use v5.14; |
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use warnings; |
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use Carp; |
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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 - dynamically change the value of a variable |
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=head1 SYNOPSIS |
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use Syntax::Keyword::Dynamically; |
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my $logger = ...; |
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sub operate |
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{ |
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dynamically $logger->level = LOG_DEBUG; |
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do_things(); |
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} |
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=head1 DESCRIPTION |
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This module provides a syntax plugin that implements a single keyword, |
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C, which alters the behaviour of a scalar assignment operation. |
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Syntactically and semantically it is similar to the built-in perl keyword |
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C, but is implemented somewhat differently to give two key advantages |
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over regular C: |
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=over 2 |
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=item * |
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You can C assign to lvalue functions and accessors. |
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=item * |
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You can C assign to regular lexical variables. |
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=back |
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Semantically, the behaviour can be considered equivalent to |
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{ |
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my $old = $VAR; |
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$VAR = "new value"; |
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... |
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$VAR = $old; |
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} |
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Except that the old value will also be restored in the case of exceptions, |
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C, C or similar ways to leave the controlling block |
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scope. |
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=cut |
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=head1 KEYWORDS |
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=head2 dynamically |
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{ |
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dynamically LVALUE = EXPR; |
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... |
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} |
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The C keyword modifies the behaviour of the following expression. |
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which must be a scalar assignment. Before the new value is assigned to the |
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lvalue, its current value is captured and stored internally within the Perl |
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interpreter. When execution leaves the controlling block for whatever reason, |
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as part of block scope cleanup the saved value is restored. |
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The LVALUE may be any kind of expression that allows normal scalar assignment; |
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lexical or package scalar variables, elements of arrays or hashes, or the |
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result of calling an C<:lvalue> function or method. |
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If the LVALUE has any GET magic associated with it (including a C |
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method of a tied scalar) then this will be executed exactly once when the |
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C expression is evaluated. |
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If the LVALUE has any SET magic associated with it (including a C |
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method of a tied scalar) then this will be executed exactly once when the |
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C expression is evaluated, and again a second time when the |
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controlling scope is unwound. |
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When the LVALUE being assigned to is a hash element, e.g. one of the following |
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forms |
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dynamically $hash{key} = EXPR; |
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dynamically $href->{key} = EXPR; |
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the assignment additionally ensures to remove the key if it is newly-added, |
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and restores by adding the key back again if it had been deleted in the |
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meantime. |
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=cut |
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sub import |
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{ |
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my $class = shift; |
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my $caller = caller; |
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$class->import_into( $caller, @_ ); |
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} |
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sub import_into |
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{ |
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my $class = shift; |
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my ( $caller, @syms ) = @_; |
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my %syms = map { $_ => 1 } @syms; |
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$^H{"Syntax::Keyword::Dynamically/dynamically"}++; |
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_enable_async_mode() if delete $syms{'-async'}; |
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croak "Unrecognised import symbols @{[ keys %syms ]}" if keys %syms; |
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} |
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=head1 WITH Future::AsyncAwait |
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As of L version 0.32, cross-module integration tests |
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assert that the C correctly works across an C boundary. |
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use Future::AsyncAwait; |
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use Syntax::Keyword::Dynamically; |
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our $var; |
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async sub trial |
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{ |
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dynamically $var = "value"; |
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await func(); |
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say "Var is still $var"; |
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} |
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When context-switching between scopes in which a variable is C |
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modified, the value of the variable will be swapped in and out, possibly |
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multiple times if necessary, to ensure the visible value remains as expected. |
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=head1 AUTHOR |
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Paul Evans |
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=cut |
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0x55AA; |