8 Scope::Upper - Act on upper scopes.
25 use Scope::Upper qw/reap localize localize_elem localize_delete UP/;
27 sub desc { shift->{desc} }
32 # First localize $x so that it gets destroyed last
33 localize '$x' => bless({ desc => $desc }, __PACKAGE__) => UP;
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 => UP; # 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) => $cx;
73 return @things; # returns to try() and then outside zap()
77 my @what = zap(); # @what contains @things
81 This module lets you defer actions that will take place when the control flow returns into an upper scope.
82 Currently, you can hook an upper scope end, or localize variables, array/hash values or deletions of elements in higher contexts.
83 You can also return to an upper level and know which context was in use then.
87 These control words are to be used to indicate the target scope.
91 Returns the level that currently represents the highest scope.
99 The level of the scope just above C<$from>.
103 The level of the scope just below C<$from>.
107 The level of the closest subroutine context above C<$from>.
111 The level of the closest eval context above C<$from>.
113 If C<$from> is omitted in any of those functions, the current level is used as the reference level.
115 =head2 C<CALLER $stack>
117 The level of the C<$stack>-th upper subroutine/eval/format context.
118 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.
126 XSLoader::load(__PACKAGE__, $VERSION);
129 =head2 C<reap $callback, $level>
131 Add a destructor that calls C<$callback> when the C<$level>-th upper scope ends, where C<0> corresponds to the current scope.
133 =head2 C<localize $what, $value, $level>
135 A C<local> delayed to the time of first return into the C<$level>-th upper scope.
142 A glob, in which case C<$value> can either be a glob or a reference.
143 L</localize> follows then the same syntax as C<local *x = $value>.
144 For example, if C<$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<$x> to C<1>.
148 A string beginning with a sigil, representing the symbol to localize and to assign to.
149 If the sigil is C<'$'>, L</localize> follows the same syntax as C<local $x = $value>, i.e. C<$value> isn't dereferenced.
152 localize '$x', \'foo' => HERE;
154 will set C<$x> to a reference to the string C<'foo'>.
155 Other sigils (C<'@'>, C<'%'>, C<'&'> and C<'*'>) require C<$value> to be a reference of the corresponding type.
157 When the symbol is given by a string, it is resolved when the actual localization takes place and not when C<localize> is called.
160 sub tag { localize '$x', $_[0] => UP }
162 will localize in the caller's namespace.
166 =head2 C<localize_elem $what, $key, $value, $level>
168 Similar to L</localize> but for array and hash elements.
169 If C<$what> is a glob, the slot to fill is determined from which type of reference C<$value> is ; otherwise it's inferred from the sigil.
170 C<$key> is either an array index or a hash key, depending of which kind of variable you localize.
172 =head2 C<localize_delete $what, $key, $level>
174 Similiar to L</localize>, but for deleting variables or array/hash elements.
181 A glob, in which case C<$key> is ignored and the call is equivalent to C<local *x>.
185 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}>.
189 A string beginning with C<'&'>, which more or less does C<undef &func> in the upper scope.
190 It's actually more powerful, as C<&func> won't even C<exists> anymore.
195 =head2 C<unwind @values, $level>
197 Returns C<@values> I<from> the context indicated by C<$level>, i.e. from the subroutine, eval or format just above C<$level>.
199 The upper level isn't coerced onto C<@values>, which is hence always evaluated in list context.
203 my @a = ('a' .. 'z');
207 will set C<$num> to C<'z'>.
208 You can use L</want_at> to handle these cases.
210 =head2 C<want_at $level>
212 Like C<wantarray>, but for the subroutine/eval/format context just above C<$level>.
214 The previous example can then be "corrected" :
217 my @a = ('a' .. 'z');
218 unwind +(want_at(HERE) ? @a : scalar @a) => HERE;
221 will righteously set C<$num> to C<26>.
225 The functions L</reap>, L</localize>, L</localize_elem>, L</localize_delete>, L</unwind> and L</want_at> are only exported on request, either individually or by the tags C<':funcs'> and C<':all'>.
227 Same goes for the words L</TOP>, L</HERE>, L</UP>, L</DOWN>, L</SUB>, L</EVAL> and L</CALLER> that are only exported on request, individually or by the tags C<':words'> and C<':all'>.
231 use base qw/Exporter/;
235 funcs => [ qw/reap localize localize_elem localize_delete unwind want_at/ ],
236 words => [ qw/TOP HERE UP DOWN SUB EVAL CALLER/ ],
238 our @EXPORT_OK = map { @$_ } values %EXPORT_TAGS;
239 $EXPORT_TAGS{'all'} = [ @EXPORT_OK ];
243 Be careful that local variables are restored in the reverse order in which they were localized.
244 Consider those examples:
248 reap sub { print $x } => HERE;
256 reap sub { $x = 2 } => HERE;
261 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>.
263 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.
264 This is an hopeless case because C<BEGIN> blocks are executed once while localizing constructs should do their job at each run.
268 L<XSLoader> (standard since perl 5.006).
272 L<Alias>, L<Hook::Scope>, L<Scope::Guard>, L<Guard>.
276 Vincent Pit, C<< <perl at profvince.com> >>, L<http://www.profvince.com>.
278 You can contact me by mail or on C<irc.perl.org> (vincent).
282 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.
286 You can find documentation for this module with the perldoc command.
290 Tests code coverage report is available at L<http://www.profvince.com/perl/cover/Scope-Upper>.
292 =head1 ACKNOWLEDGEMENTS
294 Inspired by Ricardo Signes.
296 =head1 COPYRIGHT & LICENSE
298 Copyright 2008-2009 Vincent Pit, all rights reserved.
300 This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
304 1; # End of Scope::Upper