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 # $x is now a X object, and @ARGV has one element less
55 warn 'what'; # warns "pie: what at ..."
57 } # "pie: done" is printed
61 use Scope::Upper qw/unwind want_at :words/;
64 my @result = shift->();
66 unwind +(want_at($cx) ? @result : scalar @result) => $cx;
73 return @things; # returns to try() and then outside zap()
77 my @what = zap(); # @what contains @things
81 This module lets you defer actions that will take place when the control flow returns into an upper scope.
82 Currently, you can hook an upper scope end, or localize variables, array/hash values or deletions of elements in higher contexts.
83 You can also return to an upper level and know which context was in use then.
91 XSLoader::load(__PACKAGE__, $VERSION);
94 =head2 C<reap $callback, $level>
96 Add a destructor that calls C<$callback> when the C<$level>-th upper scope ends, where C<0> corresponds to the current scope.
98 =head2 C<localize $what, $value, $level>
100 A C<local> delayed to the time of first return into the C<$level>-th upper scope.
107 A glob, in which case C<$value> can either be a glob or a reference.
108 L</localize> follows then the same syntax as C<local *x = $value>.
109 For example, if C<$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<$x> to C<1>.
113 A string beginning with a sigil, representing the symbol to localize and to assign to.
114 If the sigil is C<'$'>, L</localize> follows the same syntax as C<local $x = $value>, i.e. C<$value> isn't dereferenced.
117 localize '$x', \'foo' => 0;
119 will set C<$x> to a reference to the string C<'foo'>.
120 Other sigils (C<'@'>, C<'%'>, C<'&'> and C<'*'>) require C<$value> to be a reference of the corresponding type.
122 When the symbol is given by a string, it is resolved when the actual localization takes place and not when C<localize> is called.
125 sub tag { localize '$x', $_[0] => 1; }
127 will localize in the caller's namespace.
131 =head2 C<localize_elem $what, $key, $value, $level>
133 Similar to L</localize> but for array and hash elements.
134 If C<$what> is a glob, the slot to fill is determined from which type of reference C<$value> is ; otherwise it's inferred from the sigil.
135 C<$key> is either an array index or a hash key, depending of which kind of variable you localize.
137 =head2 C<localize_delete $what, $key, $level>
139 Similiar to L</localize>, but for deleting variables or array/hash elements.
146 A glob, in which case C<$key> is ignored and the call is equivalent to C<local *x>.
150 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}>.
154 A string beginning with C<'&'>, which more or less does C<undef &func> in the upper scope.
155 It's actually more powerful, as C<&func> won't even C<exists> anymore.
160 =head2 C<unwind @values, $level>
162 Returns C<@values> I<from> the context indicated by C<$level>, i.e. from the subroutine, eval or format just above C<$level>.
164 The upper level isn't coerced onto C<@values>, which is hence always evaluated in list context.
168 my @a = ('a' .. 'z');
172 will set C<$num> to C<'z'>.
173 You can use L</want_at> to handle these cases.
175 =head2 C<want_at $level>
177 Like C<wantarray>, but for the subroutine/eval/format context just above C<$level>.
179 The previous example can then be "corrected" :
182 my @a = ('a' .. 'z');
183 unwind +(want_at(0) ? @a : scalar @a) => 0;
186 will righteously set C<$num> to C<26>.
192 Returns the level that currently represents the highest scope.
196 The current level - i.e. C<0>.
200 The level of the scope just above C<$from>.
204 The level of the scope just below C<$from>.
208 The level of the closest subroutine context above C<$from>.
212 The level of the closest eval context above C<$from>.
214 If C<$from> is omitted in any of those functions, the current level is used as the reference level.
216 =head2 C<CALLER $stack>
218 The level of the C<$stack>-th upper subroutine/eval/format context.
219 It kind of corresponds to the context represented by C<caller $stack>, but while e.g. C<caller 0> refers to the caller context, C<CALLER 0> will refer to the top scope in the current context.
222 reap ... => CALLER(0)
224 will fire the destructor when the current subroutine/eval/format ends.
228 The functions L</reap>, L</localize>, L</localize_elem>, L</localize_delete>, L</unwind> and L</want_at> are only exported on request, either individually or by the tags C<':funcs'> and C<':all'>.
230 Same goes for the words L</TOP>, L</HERE>, L</UP>, L</DOWN>, L</SUB>, L</EVAL> and L</CALLER> that are only exported on request, individually or by the tags C<':words'> and C<':all'>.
234 use base qw/Exporter/;
238 funcs => [ qw/reap localize localize_elem localize_delete unwind want_at/ ],
239 words => [ qw/TOP HERE UP DOWN SUB EVAL CALLER/ ],
241 our @EXPORT_OK = map { @$_ } values %EXPORT_TAGS;
242 $EXPORT_TAGS{'all'} = [ @EXPORT_OK ];
246 Be careful that local variables are restored in the reverse order in which they were localized.
247 Consider those examples:
251 reap sub { print $x } => 0;
259 reap sub { $x = 2 } => 0;
264 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>.
266 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.
267 This is an hopeless case because C<BEGIN> blocks are executed once while localizing constructs should do their job at each run.
271 L<XSLoader> (standard since perl 5.006).
275 L<Alias>, L<Hook::Scope>, L<Scope::Guard>, L<Guard>.
279 Vincent Pit, C<< <perl at profvince.com> >>, L<http://www.profvince.com>.
281 You can contact me by mail or on C<irc.perl.org> (vincent).
285 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.
289 You can find documentation for this module with the perldoc command.
293 Tests code coverage report is available at L<http://www.profvince.com/perl/cover/Scope-Upper>.
295 =head1 ACKNOWLEDGEMENTS
297 Inspired by Ricardo Signes.
299 =head1 COPYRIGHT & LICENSE
301 Copyright 2008-2009 Vincent Pit, all rights reserved.
303 This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
307 1; # End of Scope::Upper