NAME Scope::Upper - Act on upper scopes. VERSION Version 0.07 SYNOPSIS package X; use Scope::Upper qw/reap localize localize_elem localize_delete :words/; sub desc { shift->{desc} } sub set_tag { my ($desc) = @_; # First localize $x so that it gets destroyed last localize '$x' => bless({ desc => $desc }, __PACKAGE__) => UP; # one scope up reap sub { my $pkg = caller; my $x = do { no strict 'refs'; ${$pkg.'::x'} }; # Get the $x in the scope print $x->desc . ": done\n"; } => SCOPE 1; # same as UP here localize_elem '%SIG', '__WARN__' => sub { my $pkg = caller; my $x = do { no strict 'refs'; ${$pkg.'::x'} }; # Get the $x in the scope CORE::warn($x->desc . ': ' . join('', @_)); } => UP CALLER 0; # same as UP here # delete last @ARGV element localize_delete '@ARGV', -1 => UP SUB HERE; # same as UP here } package Y; { X::set_tag('pie'); # $x is now a X object, and @ARGV has one element less warn 'what'; # warns "pie: what at ..." ... } # "pie: done" is printed package Z; use Scope::Upper qw/unwind want_at :words/; sub try (&) { my @result = shift->(); my $cx = SUB UP SUB; unwind +(want_at($cx) ? @result : scalar @result) => $cx; } ... sub zap { try { return @things; # returns to try() and then outside zap() } } my @what = zap(); # @what contains @things DESCRIPTION This module lets you defer actions *at run-time* that will take place when the control flow returns into an upper scope. Currently, you can: * hook an upper scope end with "reap" ; * localize variables, array/hash values or deletions of elements in higher contexts with respectively "localize", "localize_elem" and "localize_delete" ; * return values immediately to an upper level with "unwind", and know which context was in use then with "want_at". FUNCTIONS In all those functions, $context refers to the target scope. You have to use one or a combination of "WORDS" to build the $context passed to these functions. This is needed in order to ensure that the module still works when your program is ran in the debugger. The only thing you can assume is that it is an *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. "reap $callback, $context" Add a destructor that calls $callback when the upper scope represented by $context ends. "localize $what, $value, $context" A "local" delayed to the time of first return into the upper scope denoted by $context. $what can be : * A glob, in which case $value can either be a glob or a reference. "localize" follows then the same syntax as "local *x = $value". For example, if $value is a scalar reference, then the "SCALAR" slot of the glob will be set to $$value - just like "local *x = \1" sets $x to 1. * A string beginning with a sigil, representing the symbol to localize and to assign to. If the sigil is '$', "localize" follows the same syntax as "local $x = $value", i.e. $value isn't dereferenced. For example, localize '$x', \'foo' => HERE; will set $x to a reference to the string 'foo'. Other sigils ('@', '%', '&' and '*') require $value to be a reference of the corresponding type. When the symbol is given by a string, it is resolved when the actual localization takes place and not when "localize" is called. This means that sub tag { localize '$x', $_[0] => UP } will localize in the caller's namespace. "localize_elem $what, $key, $value, $context" Similar to "localize" but for array and hash elements. If $what is a glob, the slot to fill is determined from which type of reference $value is ; otherwise it's inferred from the sigil. $key is either an array index or a hash key, depending of which kind of variable you localize. "localize_delete $what, $key, $context" Similiar to "localize", but for deleting variables or array/hash elements. $what can be: * A glob, in which case $key is ignored and the call is equivalent to "local *x". * A string beginning with '@' or '%', for which the call is equivalent to respectiveley "local $a[$key]; delete $a[$key]" and "local $h{$key}; delete $h{$key}". * A string beginning with '&', which more or less does "undef &func" in the upper scope. It's actually more powerful, as &func won't even "exists" anymore. $key is ignored. "unwind @values, $context" Returns @values *from* the context pointed by $context, i.e. from the subroutine, eval or format just above $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. The upper context isn't coerced onto @values, which is hence always evaluated in list context. This means that my $num = sub { my @a = ('a' .. 'z'); unwind @a => HERE; }->(); will set $num to 'z'. You can use "want_at" to handle these cases. "want_at $context" Like "wantarray", but for the subroutine/eval/format just above $context. The previous example can then be "corrected" : my $num = sub { my @a = ('a' .. 'z'); unwind +(want_at(HERE) ? @a : scalar @a) => HERE; }->(); will righteously set $num to 26. WORDS Constants "TOP" Returns the context that currently represents the highest scope. "HERE" The context of the current scope. Getting a context from a context For any of those functions, $from is expected to be a context. When omitted, it defaults to the the current context. "UP $from" The context of the scope just above $from. "SUB $from" The context of the closest subroutine above $from. Note that $from is returned if it is already a subroutine context ; hence "SUB SUB == SUB". "EVAL $from" The context of the closest eval above $from. Note that $from is returned if it is already an eval context ; hence "EVAL EVAL == EVAL". Getting a context from a level Here, $level should denote a number of scopes above the current one. When omitted, it defaults to 0 and those functions return the same context as "HERE". "SCOPE $level" The $level-th upper context, regardless of its type. "CALLER $level" The context of the $level-th upper subroutine/eval/format. It kind of corresponds to the context represented by "caller $level", but while e.g. "caller 0" refers to the caller context, "CALLER 0" will refer to the top scope in the current context. Examples Where "reap" fires depending on the $cxt : sub { eval { sub { { reap \&cleanup => $cxt; ... } # $cxt = SCOPE(0), or HERE ... }->(); # $cxt = SCOPE(1), or UP, or SUB, or CALLER, or CALLER(0) ... }; # $cxt = SCOPE(2), or UP UP, or UP SUB, or EVAL, or CALLER(1) ... }->(); # $cxt = SCOPE(3), or SUB UP SUB, or SUB EVAL, or CALLER(2) ... Where "localize", "localize_elem" and "localize_delete" act depending on the $cxt : sub { eval { sub { { localize '$x' => 1 => $cxt; # $cxt = SCOPE(0), or HERE ... } # $cxt = SCOPE(1), or UP, or SUB, or CALLER, or CALLER(0) ... }->(); # $cxt = SCOPE(2), or UP UP, or UP SUB, or EVAL, or CALLER(1) ... }; # $cxt = SCOPE(3), or SUB UP SUB, or SUB EVAL, or CALLER(2) ... }->(); # $cxt = SCOPE(4), UP SUB UP SUB, or UP SUB EVAL, or UP CALLER(2), or TOP ... Where "unwind" and "want_at" point to depending on the $cxt: sub { eval { sub { { unwind @things => $cxt; ... } ... }->(); # $cxt = SCOPE(0 .. 1), or HERE, or UP, or SUB, or CALLER(0) ... }; # $cxt = SCOPE(2), or UP UP, or UP SUB, or EVAL, or CALLER(1) ... }->(); # $cxt = SCOPE(3), or SUB UP SUB, or SUB EVAL, or CALLER(2) ... EXPORT The functions "reap", "localize", "localize_elem", "localize_delete", "unwind" and "want_at" are only exported on request, either individually or by the tags ':funcs' and ':all'. Same goes for the words "TOP", "HERE", "UP", "SUB", "EVAL", "SCOPE" and "CALLER" that are only exported on request, individually or by the tags ':words' and ':all'. CAVEATS Be careful that local variables are restored in the reverse order in which they were localized. Consider those examples: local $x = 0; { reap sub { print $x } => HERE; local $x = 1; ... } # prints '0' ... { local $x = 1; reap sub { $x = 2 } => HERE; ... } # $x is 0 The first case is "solved" by moving the "local" before the "reap", and the second by using "localize" instead of "reap". The effects of "reap", "localize" and "localize_elem" can't cross "BEGIN" blocks, hence calling those functions in "import" is deemed to be useless. This is an hopeless case because "BEGIN" blocks are executed once while localizing constructs should do their job at each run. However, it's possible to hook the end of the current scope compilation with B::Hooks::EndOfScope. Some rare oddities may still happen when running inside the debugger. It may help to use a perl higher than 5.8.9 or 5.10.0, as they contain some context-related fixes. DEPENDENCIES XSLoader (standard since perl 5.006). SEE ALSO Alias, Hook::Scope, Scope::Guard, Guard. AUTHOR Vincent Pit, "", . You can contact me by mail or on "irc.perl.org" (vincent). BUGS Please report any bugs or feature requests to "bug-scope-upper at rt.cpan.org", or through the web interface at . I will be notified, and then you'll automatically be notified of progress on your bug as I make changes. SUPPORT You can find documentation for this module with the perldoc command. perldoc Scope::Upper Tests code coverage report is available at . ACKNOWLEDGEMENTS Inspired by Ricardo Signes. Thanks to Shawn M. Moore for motivation. COPYRIGHT & LICENSE Copyright 2008-2009 Vincent Pit, all rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself.