=head1 VERSION
-Version 0.05
+Version 0.13
=cut
our $VERSION;
BEGIN {
- $VERSION = '0.05';
+ $VERSION = '0.13';
}
=head1 SYNOPSIS
- package X;
+L</reap>, L</localize>, L</localize_elem>, L</localize_delete> and L</WORDS> :
+
+ package Scope;
use Scope::Upper qw/reap localize localize_elem localize_delete :words/;
- sub desc { shift->{desc} }
+ sub new {
+ my ($class, $name) = @_;
+
+ localize '$tag' => bless({ name => $name }, $class) => UP;
+
+ reap { print Scope->tag->name, ": end\n" } UP;
+ }
- sub set_tag {
- my ($desc) = @_;
+ # Get the tag stored in the caller namespace
+ sub tag {
+ my $l = 0;
+ my $pkg = __PACKAGE__;
+ $pkg = caller $l++ while $pkg eq __PACKAGE__;
- # First localize $x so that it gets destroyed last
- localize '$x' => bless({ desc => $desc }, __PACKAGE__) => UP; # one scope up
+ no strict 'refs';
+ ${$pkg . '::tag'};
+ }
- 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
+ sub name { shift->{name} }
+ # Locally capture warnings and reprint them with the name prefixed
+ sub catch {
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
+ print Scope->tag->name, ': ', @_;
+ } => UP;
+ }
- # delete last @ARGV element
- localize_delete '@ARGV', -1 => UP SUB HERE; # same as UP here
+ # Locally clear @INC
+ sub private {
+ for (reverse 0 .. $#INC) {
+ # First UP is the for loop, second is the sub boundary
+ localize_delete '@INC', $_ => UP UP;
+ }
}
- package Y;
+ ...
+
+ package UserLand;
{
- 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
+ Scope->new("top"); # initializes $UserLand::tag
+
+ {
+ Scope->catch;
+ my $one = 1 + undef; # prints "top: Use of uninitialized value..."
+
+ {
+ Scope->private;
+ eval { require Cwd };
+ print $@; # prints "Can't locate Cwd.pm in @INC (@INC contains:) at..."
+ }
+
+ require Cwd; # loads Cwd.pm
+ }
+
+ } # prints "top: done"
- package Z;
+L</unwind> and L</want_at> :
+
+ package Try;
use Scope::Upper qw/unwind want_at :words/;
sub try (&) {
my @result = shift->();
- my $cx = SUB UP SUB;
+ my $cx = SUB UP; # Point to the sub above this one
unwind +(want_at($cx) ? @result : scalar @result) => $cx;
}
sub zap {
try {
+ my @things = qw/a b c/;
return @things; # returns to try() and then outside zap()
- }
+ # not reached
+ };
+ # not reached
}
- my @what = zap(); # @what contains @things
+ my @stuff = zap(); # @stuff contains qw/a b c/
+ my $stuff = zap(); # $stuff contains 3
=head1 DESCRIPTION
-This module lets you defer actions that will take place when the control flow returns into an upper scope.
-Currently, you can hook an upper scope end, or localize variables, array/hash values or deletions of elements in higher contexts.
-You can also return to an upper level and know which context was in use then.
+This module lets you defer actions I<at run-time> that will take place when the control flow returns into an upper scope.
+Currently, you can:
+
+=over 4
+
+=item *
+
+hook an upper scope end with L</reap> ;
+
+=item *
+
+localize variables, array/hash values or deletions of elements in higher contexts with respectively L</localize>, L</localize_elem> and L</localize_delete> ;
+
+=item *
+
+return values immediately to an upper level with L</unwind>, and know which context was in use then with L</want_at>.
+
+=back
=head1 FUNCTIONS
In all those functions, C<$context> refers to the target scope.
-You have to use one or a combination of L</WORDS> to build the C<$context> to pass to these functions.
+You have to use one or a combination of L</WORDS> to build the C<$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.
-Don't try to use a raw value or things will get messy.
-
-The only thing you can assume is that it is an I<absolute> indicator of the frame.
-This means that you can safely store it at some point and use it when needed, and it will still denote the original scope.
+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.
=cut
=head2 C<reap $callback, $context>
-Add a destructor that calls C<$callback> when the upper scope represented by C<$context> ends.
+Adds a destructor that calls C<$callback> (in void context) when the upper scope represented by C<$context> ends.
=head2 C<localize $what, $value, $context>
-A C<local> delayed to the time of first return into the upper scope denoted by C<$context>.
+Introduces a C<local> delayed to the time of first return into the upper scope denoted by C<$context>.
C<$what> can be :
=over 4
will set C<$x> to a reference to the string C<'foo'>.
Other sigils (C<'@'>, C<'%'>, C<'&'> and C<'*'>) require C<$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 C<localize> is called.
-This means that
+When the symbol is given by a string, it is resolved when the actual localization takes place and not when L</localize> is called.
+Thus, if the symbol name is not qualified, it will refer to the variable in the package where the localization actually takes place and not in the one where the L</localize> call was compiled.
+For example,
- sub tag { localize '$x', $_[0] => UP }
+ {
+ package Scope;
+ sub new { localize '$tag', $_[0] => UP }
+ }
-will localize in the caller's namespace.
+ {
+ package Tool;
+ {
+ Scope->new;
+ ...
+ }
+ }
+
+will localize C<$Tool::tag> and not C<$Scope::tag>.
+If you want the other behaviour, you just have to specify C<$what> as a glob or a qualified name.
+
+Note that if C<$what> is a string denoting a variable that wasn't declared beforehand, the relevant slot will be vivified as needed and won't be deleted from the glob when the localization ends.
+This situation never arises with C<local> because it only compiles when the localized variable is already declared.
+Although I believe it shouldn't be a problem as glob slots definedness is pretty much an implementation detail, this behaviour may change in the future if proved harmful.
=back
=head2 C<localize_elem $what, $key, $value, $context>
-Similar to L</localize> but for array and hash elements.
-If C<$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.
+Introduces a C<local $what[$key] = $value> or C<local $what{$key} = $value> delayed to the time of first return into the upper scope denoted by C<$context>.
+Unlike L</localize>, C<$what> must be a string and the type of localization is inferred from its sigil.
+The two only valid types are array and hash ; for anything besides those, L</localize_elem> will throw an exception.
C<$key> is either an array index or a hash key, depending of which kind of variable you localize.
+If C<$what> is a string pointing to an undeclared variable, the variable will be vivified as soon as the localization occurs and emptied when it ends, although it will still exist in its glob.
+
=head2 C<localize_delete $what, $key, $context>
-Similiar to L</localize>, but for deleting variables or array/hash elements.
+Introduces the deletion of a variable or an array/hash element delayed to the time of first return into the upper scope denoted by C<$context>.
C<$what> can be:
=over 4
=head2 C<unwind @values, $context>
-Returns C<@values> I<from> the context pointed by C<$context>, i.e. from the subroutine, eval or format just above C<$context>.
+Returns C<@values> I<from> the context pointed by C<$context>, i.e. from the subroutine, eval or format at or just above C<$context>, and immediately restart the program flow at this point - thus effectively returning to an upper scope.
The upper context isn't coerced onto C<@values>, which is hence always evaluated in list context.
This means that
my $num = sub {
my @a = ('a' .. 'z');
unwind @a => HERE;
+ # not reached
}->();
will set C<$num> to C<'z'>.
=head2 C<want_at $context>
-Like C<wantarray>, but for the subroutine/eval/format just above C<$context>.
+Like C<wantarray>, but for the subroutine/eval/format at or just above C<$context>.
The previous example can then be "corrected" :
my $num = sub {
my @a = ('a' .. 'z');
unwind +(want_at(HERE) ? @a : scalar @a) => HERE;
+ # not reached
}->();
-will righteously set C<$num> to C<26>.
+will rightfully set C<$num> to C<26>.
+
+=head1 CONSTANTS
+
+=head2 C<SU_THREADSAFE>
+
+True iff the module could have been built when thread-safety features.
=head1 WORDS
=head3 C<SUB $from>
The context of the closest subroutine above C<$from>.
+Note that C<$from> is returned if it is already a subroutine context ; hence C<SUB SUB == SUB>.
=head3 C<EVAL $from>
The context of the closest eval above C<$from>.
+Note that C<$from> is returned if it is already an eval context ; hence C<EVAL EVAL == EVAL>.
=head2 Getting a context from a level
The context of the C<$level>-th upper subroutine/eval/format.
It kind of corresponds to the context represented by C<caller $level>, but while e.g. C<caller 0> refers to the caller context, C<CALLER 0> will refer to the top scope in the current context.
+=head2 Examples
+
+Where L</reap> fires depending on the C<$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)
+ ...
+ }->(); # $cxt = SCOPE(3), or SUB UP SUB, or SUB EVAL, or CALLER(2)
+ ...
+
+Where L</localize>, L</localize_elem> and L</localize_delete> act depending on the C<$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)
+ ...
+ }->();
+ # $cxt = SCOPE(4), UP SUB UP SUB, or UP SUB EVAL, or UP CALLER(2), or TOP
+ ...
+
+Where L</unwind> and L</want_at> point to depending on the C<$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)
+ ...
+ }->(); # $cxt = SCOPE(3), or SUB UP SUB, or SUB EVAL, or CALLER(2)
+ ...
+
=head1 EXPORT
The functions L</reap>, L</localize>, L</localize_elem>, L</localize_delete>, L</unwind> and L</want_at> are only exported on request, either individually or by the tags C<':funcs'> and C<':all'>.
+The constant L</SU_THREADSAFE> is also only exported on request, individually or by the tags C<':consts'> and C<':all'>.
+
Same goes for the words L</TOP>, L</HERE>, L</UP>, L</SUB>, L</EVAL>, L</SCOPE> and L</CALLER> that are only exported on request, individually or by the tags C<':words'> and C<':all'>.
=cut
our @EXPORT = ();
our %EXPORT_TAGS = (
- funcs => [ qw/reap localize localize_elem localize_delete unwind want_at/ ],
- words => [ qw/TOP HERE UP SUB EVAL SCOPE CALLER/ ],
+ funcs => [ qw/reap localize localize_elem localize_delete unwind want_at/ ],
+ words => [ qw/TOP HERE UP SUB EVAL SCOPE CALLER/ ],
+ consts => [ qw/SU_THREADSAFE/ ],
);
our @EXPORT_OK = map { @$_ } values %EXPORT_TAGS;
$EXPORT_TAGS{'all'} = [ @EXPORT_OK ];
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>.
-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.
+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.
This is an hopeless case because C<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 L<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 fixes.
+It may help to use a perl higher than 5.8.9 or 5.10.0, as they contain some context-related fixes.
=head1 DEPENDENCIES
=head1 SEE ALSO
+L<perlfunc/local>, L<perlsub/"Temporary Values via local()">.
+
L<Alias>, L<Hook::Scope>, L<Scope::Guard>, L<Guard>.
+L<Continuation::Escape> is a thin wrapper around L<Scope::Upper> that gives you a continuation passing style interface to L</unwind>.
+It's easier to use, but it requires you to have control over the scope where you want to return.
+
+L<Scope::Escape>.
+
=head1 AUTHOR
Vincent Pit, C<< <perl at profvince.com> >>, L<http://www.profvince.com>.
=head1 BUGS
-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.
+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.
=head1 SUPPORT
=head1 COPYRIGHT & LICENSE
-Copyright 2008-2009 Vincent Pit, all rights reserved.
+Copyright 2008,2009,2010 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.
projects / perl / modules / Scope-Upper.git / blobdiff