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 closest subroutine context above C<$from>.
107 The level of the closest eval context above C<$from>.
109 If C<$from> is omitted in any of those functions, the current level is used as the reference level.
111 =head2 C<CALLER $stack>
113 The level of the C<$stack>-th upper subroutine/eval/format context.
114 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.
122 XSLoader::load(__PACKAGE__, $VERSION);
125 =head2 C<reap $callback, $level>
127 Add a destructor that calls C<$callback> when the C<$level>-th upper scope ends, where C<0> corresponds to the current scope.
129 =head2 C<localize $what, $value, $level>
131 A C<local> delayed to the time of first return into the C<$level>-th upper scope.
138 A glob, in which case C<$value> can either be a glob or a reference.
139 L</localize> follows then the same syntax as C<local *x = $value>.
140 For example, if C<$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<$x> to C<1>.
144 A string beginning with a sigil, representing the symbol to localize and to assign to.
145 If the sigil is C<'$'>, L</localize> follows the same syntax as C<local $x = $value>, i.e. C<$value> isn't dereferenced.
148 localize '$x', \'foo' => HERE;
150 will set C<$x> to a reference to the string C<'foo'>.
151 Other sigils (C<'@'>, C<'%'>, C<'&'> and C<'*'>) require C<$value> to be a reference of the corresponding type.
153 When the symbol is given by a string, it is resolved when the actual localization takes place and not when C<localize> is called.
156 sub tag { localize '$x', $_[0] => UP }
158 will localize in the caller's namespace.
162 =head2 C<localize_elem $what, $key, $value, $level>
164 Similar to L</localize> but for array and hash elements.
165 If C<$what> is a glob, the slot to fill is determined from which type of reference C<$value> is ; otherwise it's inferred from the sigil.
166 C<$key> is either an array index or a hash key, depending of which kind of variable you localize.
168 =head2 C<localize_delete $what, $key, $level>
170 Similiar to L</localize>, but for deleting variables or array/hash elements.
177 A glob, in which case C<$key> is ignored and the call is equivalent to C<local *x>.
181 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}>.
185 A string beginning with C<'&'>, which more or less does C<undef &func> in the upper scope.
186 It's actually more powerful, as C<&func> won't even C<exists> anymore.
191 =head2 C<unwind @values, $level>
193 Returns C<@values> I<from> the context indicated by C<$level>, i.e. from the subroutine, eval or format just above C<$level>.
195 The upper level isn't coerced onto C<@values>, which is hence always evaluated in list context.
199 my @a = ('a' .. 'z');
203 will set C<$num> to C<'z'>.
204 You can use L</want_at> to handle these cases.
206 =head2 C<want_at $level>
208 Like C<wantarray>, but for the subroutine/eval/format context just above C<$level>.
210 The previous example can then be "corrected" :
213 my @a = ('a' .. 'z');
214 unwind +(want_at(HERE) ? @a : scalar @a) => HERE;
217 will righteously set C<$num> to C<26>.
221 The functions L</reap>, L</localize>, L</localize_elem>, L</localize_delete>, L</unwind> and L</want_at> are only exported on request, either individually or by the tags C<':funcs'> and C<':all'>.
223 Same goes for the words L</TOP>, L</HERE>, L</UP>, L</SUB>, L</EVAL> and L</CALLER> that are only exported on request, individually or by the tags C<':words'> and C<':all'>.
227 use base qw/Exporter/;
231 funcs => [ qw/reap localize localize_elem localize_delete unwind want_at/ ],
232 words => [ qw/TOP HERE UP SUB EVAL CALLER/ ],
234 our @EXPORT_OK = map { @$_ } values %EXPORT_TAGS;
235 $EXPORT_TAGS{'all'} = [ @EXPORT_OK ];
239 Be careful that local variables are restored in the reverse order in which they were localized.
240 Consider those examples:
244 reap sub { print $x } => HERE;
252 reap sub { $x = 2 } => HERE;
257 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>.
259 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.
260 This is an hopeless case because C<BEGIN> blocks are executed once while localizing constructs should do their job at each run.
264 L<XSLoader> (standard since perl 5.006).
268 L<Alias>, L<Hook::Scope>, L<Scope::Guard>, L<Guard>.
272 Vincent Pit, C<< <perl at profvince.com> >>, L<http://www.profvince.com>.
274 You can contact me by mail or on C<irc.perl.org> (vincent).
278 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.
282 You can find documentation for this module with the perldoc command.
286 Tests code coverage report is available at L<http://www.profvince.com/perl/cover/Scope-Upper>.
288 =head1 ACKNOWLEDGEMENTS
290 Inspired by Ricardo Signes.
292 =head1 COPYRIGHT & LICENSE
294 Copyright 2008-2009 Vincent Pit, all rights reserved.
296 This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
300 1; # End of Scope::Upper