8 Scope::Upper - Act on upper scopes.
25 use Scope::Upper qw/reap localize localize_elem localize_delete/;
27 sub desc { shift->{desc} }
32 # First localize $x so that it gets destroyed last
33 localize '$x' => bless({ desc => $desc }, __PACKAGE__) => 1;
37 my $x = do { no strict 'refs'; ${$pkg.'::x'} }; # Get the $x in the scope
38 print $x->desc . ": done\n";
41 localize_elem '%SIG', '__WARN__' => sub {
43 my $x = do { no strict 'refs'; ${$pkg.'::x'} }; # Get the $x in the scope
44 CORE::warn($x->desc . ': ' . join('', @_));
47 localize_delete '@ARGV', $#ARGV => 1; # delete last @ARGV element
54 # $x is now a X object, and @ARGV has one element less
55 warn 'what'; # warns "pie: what at ..."
57 } # "pie: done" is printed
61 This module lets you defer actions that will take place when the control flow returns into an upper scope.
62 Currently, you can hook an upper scope end, or localize variables, array/hash values or deletions of elements in higher contexts.
70 XSLoader::load(__PACKAGE__, $VERSION);
73 =head2 C<reap $callback, $level>
75 Add a destructor that calls C<$callback> when the C<$level>-th upper scope ends, where C<0> corresponds to the current scope.
77 =head2 C<localize $what, $value, $level>
79 A C<local> delayed to the time of first return into the C<$level>-th upper scope.
86 A glob, in which case C<$value> can either be a glob or a reference.
87 L</localize> follows then the same syntax as C<local *x = $value>.
88 For example, if C<$value> is a scalar reference, then the C<SCALAR> slot of the glob will be set to C<$$value> - just like C<local *x = \1> sets C<$x> to C<1>.
92 A string beginning with a sigil, representing the symbol to localize and to assign to.
93 If the sigil is C<'$'>, L</localize> follows the same syntax as C<local $x = $value>, i.e. C<$value> isn't dereferenced.
96 localize '$x', \'foo' => 0;
98 will set C<$x> to a reference to the string C<'foo'>.
99 Other sigils (C<'@'>, C<'%'>, C<'&'> and C<'*'>) require C<$value> to be a reference of the corresponding type.
101 When the symbol is given by a string, it is resolved when the actual localization takes place and not when C<localize> is called.
104 sub tag { localize '$x', $_[0] => 1; }
106 will localize in the caller's namespace.
110 =head2 C<localize_elem $what, $key, $value, $level>
112 Similar to L</localize> but for array and hash elements.
113 If C<$what> is a glob, the slot to fill is determined from which type of reference C<$value> is ; otherwise it's inferred from the sigil.
114 C<$key> is either an array index or a hash key, depending of which kind of variable you localize.
116 =head2 C<localize_delete $what, $key, $level>
118 Similiar to L</localize>, but for deleting variables or array/hash elements.
125 A glob, in which case C<$key> is ignored and the call is equivalent to C<local *x>.
129 A string beginning with C<'@'> or C<'%'>, for which the call is equivalent to respectiveley C<local $a[$key]; delete $a[$key]> and C<local $h{$key}; delete $h{$key}>.
133 A string beginning with C<'&'>, which more or less does C<undef &func> in the upper scope.
134 It's actually more powerful, as C<&func> won't even C<exists> anymore.
139 =head2 C<unwind @values, $level>
141 Returns C<@values> I<from> the context indicated by C<$level>, i.e. from the subroutine, eval or format just above C<$level>.
142 The upper level isn't coerced onto C<@values>, which is hence always evaluated in list context.
144 =head2 C<want_at $level>
146 Like C<wantarray>, but for the subroutine/eval/format context just above C<$level>.
152 Returns the level that currently represents the highest scope.
156 The current level - i.e. C<0>.
160 The level of the scope just above C<$from>.
164 The level of the scope just below C<$from>.
168 The level of the closest subroutine context above C<$from>.
172 The level of the closest eval context above C<$from>.
174 If C<$from> is omitted in any of those functions, the current level is used as the reference level.
176 =head2 C<CALLER $stack>
178 The level corresponding to the stack referenced by C<caller $stack>.
182 The functions L</reap>, L</localize>, L</localize_elem>, L</localize_delete>, L</unwind> and L</want_at> are only exported on request, either individually or by the tags C<':funcs'> and C<':all'>.
184 Same goes for the words L</TOP>, L</HERE>, L</UP>, L</DOWN>, L</SUB>, L</EVAL> and L</CALLER> that are only exported on request, individually or by the tags C<':words'> and C<':all'>.
188 use base qw/Exporter/;
192 funcs => [ qw/reap localize localize_elem localize_delete unwind want_at/ ],
193 words => [ qw/TOP HERE UP DOWN SUB EVAL CALLER/ ],
195 our @EXPORT_OK = map { @$_ } values %EXPORT_TAGS;
196 $EXPORT_TAGS{'all'} = [ @EXPORT_OK ];
200 Be careful that local variables are restored in the reverse order in which they were localized.
201 Consider those examples:
205 reap sub { print $x } => 0;
213 reap sub { $x = 2 } => 0;
218 The first case is "solved" by moving the C<local> before the C<reap>, and the second by using L</localize> instead of L</reap>.
220 L</reap>, L</localize> and L</localize_elem> effects can't cross C<BEGIN> blocks, hence calling those functions in C<import> is deemed to be useless.
221 This is an hopeless case because C<BEGIN> blocks are executed once while localizing constructs should do their job at each run.
225 L<XSLoader> (standard since perl 5.006).
229 L<Alias>, L<Hook::Scope>, L<Scope::Guard>, L<Guard>.
233 Vincent Pit, C<< <perl at profvince.com> >>, L<http://www.profvince.com>.
235 You can contact me by mail or on C<irc.perl.org> (vincent).
239 Please report any bugs or feature requests to C<bug-scope-upper at rt.cpan.org>, or through the web interface at L<http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Scope-Upper>. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.
243 You can find documentation for this module with the perldoc command.
247 Tests code coverage report is available at L<http://www.profvince.com/perl/cover/Scope-Upper>.
249 =head1 ACKNOWLEDGEMENTS
251 Inspired by Ricardo Signes.
253 =head1 COPYRIGHT & LICENSE
255 Copyright 2008-2009 Vincent Pit, all rights reserved.
257 This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
261 1; # End of Scope::Upper