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.
90 XSLoader::load(__PACKAGE__, $VERSION);
93 =head2 C<reap $callback, $level>
95 Add a destructor that calls C<$callback> when the C<$level>-th upper scope ends, where C<0> corresponds to the current scope.
97 =head2 C<localize $what, $value, $level>
99 A C<local> delayed to the time of first return into the C<$level>-th upper scope.
106 A glob, in which case C<$value> can either be a glob or a reference.
107 L</localize> follows then the same syntax as C<local *x = $value>.
108 For example, if C<$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<$x> to C<1>.
112 A string beginning with a sigil, representing the symbol to localize and to assign to.
113 If the sigil is C<'$'>, L</localize> follows the same syntax as C<local $x = $value>, i.e. C<$value> isn't dereferenced.
116 localize '$x', \'foo' => 0;
118 will set C<$x> to a reference to the string C<'foo'>.
119 Other sigils (C<'@'>, C<'%'>, C<'&'> and C<'*'>) require C<$value> to be a reference of the corresponding type.
121 When the symbol is given by a string, it is resolved when the actual localization takes place and not when C<localize> is called.
124 sub tag { localize '$x', $_[0] => 1; }
126 will localize in the caller's namespace.
130 =head2 C<localize_elem $what, $key, $value, $level>
132 Similar to L</localize> but for array and hash elements.
133 If C<$what> is a glob, the slot to fill is determined from which type of reference C<$value> is ; otherwise it's inferred from the sigil.
134 C<$key> is either an array index or a hash key, depending of which kind of variable you localize.
136 =head2 C<localize_delete $what, $key, $level>
138 Similiar to L</localize>, but for deleting variables or array/hash elements.
145 A glob, in which case C<$key> is ignored and the call is equivalent to C<local *x>.
149 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}>.
153 A string beginning with C<'&'>, which more or less does C<undef &func> in the upper scope.
154 It's actually more powerful, as C<&func> won't even C<exists> anymore.
159 =head2 C<unwind @values, $level>
161 Returns C<@values> I<from> the context indicated by C<$level>, i.e. from the subroutine, eval or format just above C<$level>.
162 The upper level isn't coerced onto C<@values>, which is hence always evaluated in list context.
164 =head2 C<want_at $level>
166 Like C<wantarray>, but for the subroutine/eval/format context just above C<$level>.
172 Returns the level that currently represents the highest scope.
176 The current level - i.e. C<0>.
180 The level of the scope just above C<$from>.
184 The level of the scope just below C<$from>.
188 The level of the closest subroutine context above C<$from>.
192 The level of the closest eval context above C<$from>.
194 If C<$from> is omitted in any of those functions, the current level is used as the reference level.
196 =head2 C<CALLER $stack>
198 The level corresponding to the stack referenced by C<caller $stack>.
202 The functions L</reap>, L</localize>, L</localize_elem>, L</localize_delete>, L</unwind> and L</want_at> are only exported on request, either individually or by the tags C<':funcs'> and C<':all'>.
204 Same goes for the words L</TOP>, L</HERE>, L</UP>, L</DOWN>, L</SUB>, L</EVAL> and L</CALLER> that are only exported on request, individually or by the tags C<':words'> and C<':all'>.
208 use base qw/Exporter/;
212 funcs => [ qw/reap localize localize_elem localize_delete unwind want_at/ ],
213 words => [ qw/TOP HERE UP DOWN SUB EVAL CALLER/ ],
215 our @EXPORT_OK = map { @$_ } values %EXPORT_TAGS;
216 $EXPORT_TAGS{'all'} = [ @EXPORT_OK ];
220 Be careful that local variables are restored in the reverse order in which they were localized.
221 Consider those examples:
225 reap sub { print $x } => 0;
233 reap sub { $x = 2 } => 0;
238 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>.
240 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.
241 This is an hopeless case because C<BEGIN> blocks are executed once while localizing constructs should do their job at each run.
245 L<XSLoader> (standard since perl 5.006).
249 L<Alias>, L<Hook::Scope>, L<Scope::Guard>, L<Guard>.
253 Vincent Pit, C<< <perl at profvince.com> >>, L<http://www.profvince.com>.
255 You can contact me by mail or on C<irc.perl.org> (vincent).
259 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.
263 You can find documentation for this module with the perldoc command.
267 Tests code coverage report is available at L<http://www.profvince.com/perl/cover/Scope-Upper>.
269 =head1 ACKNOWLEDGEMENTS
271 Inspired by Ricardo Signes.
273 =head1 COPYRIGHT & LICENSE
275 Copyright 2008-2009 Vincent Pit, all rights reserved.
277 This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
281 1; # End of Scope::Upper