8 Scope::Upper - Act on upper scopes.
25 use Scope::Upper qw/reap localize localize_elem localize_delete :words/;
27 sub desc { shift->{desc} }
32 # First localize $x so that it gets destroyed last
33 localize '$x' => bless({ desc => $desc }, __PACKAGE__) => UP; # one scope up
37 my $x = do { no strict 'refs'; ${$pkg.'::x'} }; # Get the $x in the scope
38 print $x->desc . ": done\n";
39 } => SCOPE 1; # same as UP here
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('', @_));
45 } => UP CALLER 0; # same as UP here
47 # delete last @ARGV element
48 localize_delete '@ARGV', -1 => UP SUB HERE; # same as UP here
55 # $x is now a X object, and @ARGV has one element less
56 warn 'what'; # warns "pie: what at ..."
58 } # "pie: done" is printed
62 use Scope::Upper qw/unwind want_at :words/;
65 my @result = shift->();
67 unwind +(want_at($cx) ? @result : scalar @result) => $cx;
74 return @things; # returns to try() and then outside zap()
78 my @what = zap(); # @what contains @things
82 This module lets you defer actions I<at run-time> that will take place when the control flow returns into an upper scope.
89 hook an upper scope end with L</reap> ;
93 localize variables, array/hash values or deletions of elements in higher contexts with respectively L</localize>, L</localize_elem> and L</localize_delete> ;
97 return values immediately to an upper level with L</unwind>, and know which context was in use then with L</want_at>.
103 In all those functions, C<$context> refers to the target scope.
105 You have to use one or a combination of L</WORDS> to build the C<$context> passed to these functions.
106 This is needed in order to ensure that the module still works when your program is ran in the debugger.
107 The only thing you can assume is that it is an I<absolute> indicator of the frame, which means that you can safely store it at some point and use it when needed, and it will still denote the original scope.
113 XSLoader::load(__PACKAGE__, $VERSION);
116 =head2 C<reap $callback, $context>
118 Add a destructor that calls C<$callback> when the upper scope represented by C<$context> ends.
120 =head2 C<localize $what, $value, $context>
122 A C<local> delayed to the time of first return into the upper scope denoted by C<$context>.
129 A glob, in which case C<$value> can either be a glob or a reference.
130 L</localize> follows then the same syntax as C<local *x = $value>.
131 For example, if C<$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<$x> to C<1>.
135 A string beginning with a sigil, representing the symbol to localize and to assign to.
136 If the sigil is C<'$'>, L</localize> follows the same syntax as C<local $x = $value>, i.e. C<$value> isn't dereferenced.
139 localize '$x', \'foo' => HERE;
141 will set C<$x> to a reference to the string C<'foo'>.
142 Other sigils (C<'@'>, C<'%'>, C<'&'> and C<'*'>) require C<$value> to be a reference of the corresponding type.
144 When the symbol is given by a string, it is resolved when the actual localization takes place and not when C<localize> is called.
147 sub tag { localize '$x', $_[0] => UP }
149 will localize in the caller's namespace.
153 =head2 C<localize_elem $what, $key, $value, $context>
155 Similar to L</localize> but for array and hash elements.
156 If C<$what> is a glob, the slot to fill is determined from which type of reference C<$value> is ; otherwise it's inferred from the sigil.
157 C<$key> is either an array index or a hash key, depending of which kind of variable you localize.
159 =head2 C<localize_delete $what, $key, $context>
161 Similiar to L</localize>, but for deleting variables or array/hash elements.
168 A glob, in which case C<$key> is ignored and the call is equivalent to C<local *x>.
172 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}>.
176 A string beginning with C<'&'>, which more or less does C<undef &func> in the upper scope.
177 It's actually more powerful, as C<&func> won't even C<exists> anymore.
182 =head2 C<unwind @values, $context>
184 Returns C<@values> I<from> the context pointed by C<$context>, i.e. from the subroutine, eval or format just above C<$context>, and immediately restart the program flow at this point - thus effectively returning to (or from, depending on how you see it) an upper context.
186 The upper context isn't coerced onto C<@values>, which is hence always evaluated in list context.
190 my @a = ('a' .. 'z');
194 will set C<$num> to C<'z'>.
195 You can use L</want_at> to handle these cases.
197 =head2 C<want_at $context>
199 Like C<wantarray>, but for the subroutine/eval/format just above C<$context>.
201 The previous example can then be "corrected" :
204 my @a = ('a' .. 'z');
205 unwind +(want_at(HERE) ? @a : scalar @a) => HERE;
208 will righteously set C<$num> to C<26>.
216 Returns the context that currently represents the highest scope.
220 The context of the current scope.
222 =head2 Getting a context from a context
224 For any of those functions, C<$from> is expected to be a context.
225 When omitted, it defaults to the the current context.
229 The context of the scope just above C<$from>.
233 The context of the closest subroutine above C<$from>.
237 The context of the closest eval above C<$from>.
239 =head2 Getting a context from a level
241 Here, C<$level> should denote a number of scopes above the current one.
242 When omitted, it defaults to C<0> and those functions return the same context as L</HERE>.
244 =head3 C<SCOPE $level>
246 The C<$level>-th upper context, regardless of its type.
248 =head3 C<CALLER $level>
250 The context of the C<$level>-th upper subroutine/eval/format.
251 It kind of corresponds to the context represented by C<caller $level>, but while e.g. C<caller 0> refers to the caller context, C<CALLER 0> will refer to the top scope in the current context.
255 Where L</reap> fires depending on the C<$cxt> :
261 reap \&cleanup => $cxt;
263 } # $cxt = SCOPE(0), or HERE
265 }->(); # $cxt = SCOPE(1), or UP, or SUB, or CALLER, or CALLER(0)
267 }; # $cxt = SCOPE(2), or UP UP, or UP SUB, or EVAL, or CALLER(1)
269 }->(); # $cxt = SCOPE(3), or SUB UP SUB, or SUB EVAL, or CALLER(2)
272 Where L</localize>, L</localize_elem> and L</localize_delete> act depending on the C<$cxt> :
278 localize '$x' => 1 => $cxt;
279 # $cxt = SCOPE(0), or HERE
282 # $cxt = SCOPE(1), or UP, or SUB, or CALLER, or CALLER(0)
285 # $cxt = SCOPE(2), or UP UP, or UP SUB, or EVAL, or CALLER(1)
288 # $cxt = SCOPE(3), or SUB UP SUB, or SUB EVAL, or CALLER(2)
291 # $cxt = SCOPE(4), UP SUB UP SUB, or UP SUB EVAL, or UP CALLER(2), or TOP
294 Where L</unwind> and L</want_at> point to depending on the C<$cxt>:
300 unwind @things => $cxt;
304 }->(); # $cxt = SCOPE(0 .. 1), or HERE, or UP, or SUB, or CALLER(0)
306 }; # $cxt = SCOPE(2), or UP UP, or UP SUB, or EVAL, or CALLER(1)
308 }->(); # $cxt = SCOPE(3), or SUB UP SUB, or SUB EVAL, or CALLER(2)
313 The functions L</reap>, L</localize>, L</localize_elem>, L</localize_delete>, L</unwind> and L</want_at> are only exported on request, either individually or by the tags C<':funcs'> and C<':all'>.
315 Same goes for the words L</TOP>, L</HERE>, L</UP>, L</SUB>, L</EVAL>, L</SCOPE> and L</CALLER> that are only exported on request, individually or by the tags C<':words'> and C<':all'>.
319 use base qw/Exporter/;
323 funcs => [ qw/reap localize localize_elem localize_delete unwind want_at/ ],
324 words => [ qw/TOP HERE UP SUB EVAL SCOPE CALLER/ ],
326 our @EXPORT_OK = map { @$_ } values %EXPORT_TAGS;
327 $EXPORT_TAGS{'all'} = [ @EXPORT_OK ];
331 Be careful that local variables are restored in the reverse order in which they were localized.
332 Consider those examples:
336 reap sub { print $x } => HERE;
344 reap sub { $x = 2 } => HERE;
349 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>.
351 The effects of L</reap>, L</localize> and L</localize_elem> can't cross C<BEGIN> blocks, hence calling those functions in C<import> is deemed to be useless.
352 This is an hopeless case because C<BEGIN> blocks are executed once while localizing constructs should do their job at each run.
353 However, it's possible to hook the end of the current scope compilation with L<B::Hooks::EndOfScope>.
355 Some rare oddities may still happen when running inside the debugger.
356 It may help to use a perl higher than 5.8.9 or 5.10.0, as they contain some context-related fixes.
360 L<XSLoader> (standard since perl 5.006).
364 L<Alias>, L<Hook::Scope>, L<Scope::Guard>, L<Guard>.
368 Vincent Pit, C<< <perl at profvince.com> >>, L<http://www.profvince.com>.
370 You can contact me by mail or on C<irc.perl.org> (vincent).
374 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.
378 You can find documentation for this module with the perldoc command.
382 Tests code coverage report is available at L<http://www.profvince.com/perl/cover/Scope-Upper>.
384 =head1 ACKNOWLEDGEMENTS
386 Inspired by Ricardo Signes.
388 Thanks to Shawn M. Moore for motivation.
390 =head1 COPYRIGHT & LICENSE
392 Copyright 2008-2009 Vincent Pit, all rights reserved.
394 This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
398 1; # End of Scope::Upper