Scope::Upper - Act on upper scopes.
VERSION
- Version 0.04
+ Version 0.10
SYNOPSIS
package X;
- use Scope::Upper qw/reap localize localize_elem localize_delete/;
+ use Scope::Upper qw/reap localize localize_elem localize_delete :words/;
sub desc { shift->{desc} }
my ($desc) = @_;
# First localize $x so that it gets destroyed last
- localize '$x' => bless({ desc => $desc }, __PACKAGE__) => 1;
+ localize '$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";
- } => 1;
+ } => 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('', @_));
- } => 1;
+ } => UP CALLER 0; # same as UP here
- localize_delete '@ARGV', $#ARGV => 1; # delete last @ARGV element
+ # delete last @ARGV element
+ localize_delete '@ARGV', -1 => UP SUB HERE; # same as UP here
}
package Y;
sub zap {
try {
return @things; # returns to try() and then outside zap()
+ # not reached
}
+ # not reached
}
my @what = zap(); # @what contains @things
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.
+ 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
- "reap $callback, $level"
- Add a destructor that calls $callback when the $level-th upper scope
- ends, where 0 corresponds to the current scope.
+ 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 (in void context) when the upper
+ scope represented by $context ends.
- "localize $what, $value, $level"
- A "local" delayed to the time of first return into the $level-th upper
- scope. $what can be :
+ "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
syntax as "local $x = $value", i.e. $value isn't dereferenced. For
example,
- localize '$x', \'foo' => 0;
+ localize '$x', \'foo' => HERE;
will set $x to a reference to the string 'foo'. Other sigils ('@',
'%', '&' and '*') require $value to be a reference of the
localization takes place and not when "localize" is called. This
means that
- sub tag { localize '$x', $_[0] => 1; }
+ sub tag { localize '$x', $_[0] => UP }
will localize in the caller's namespace.
- "localize_elem $what, $key, $value, $level"
+ "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, $level"
+ "localize_delete $what, $key, $context"
Similiar to "localize", but for deleting variables or array/hash
elements. $what can be:
in the upper scope. It's actually more powerful, as &func won't even
"exists" anymore. $key is ignored.
- "unwind @values, $level"
- Returns @values *from* the context indicated by $level, i.e. from the
- subroutine, eval or format just above $level. The upper level isn't
- coerced onto @values, which is hence always evaluated in list context.
+ "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.
- "want_at $level"
- Like "wantarray", but for the subroutine/eval/format context just above
- $level.
+ The upper context isn't coerced onto @values, which is hence always
+ evaluated in list context. This means that
-WORDS
- "TOP"
- Returns the level that currently represents the highest scope.
+ my $num = sub {
+ my @a = ('a' .. 'z');
+ unwind @a => HERE;
+ # not reached
+ }->();
- "HERE"
- The current level - i.e. 0.
+ will set $num to 'z'. You can use "want_at" to handle these cases.
- "UP $from"
- The level of the scope just above $from.
+ "want_at $context"
+ Like "wantarray", but for the subroutine/eval/format just above
+ $context.
- "DOWN $from"
- The level of the scope just below $from.
+ The previous example can then be "corrected" :
- "SUB $from"
- The level of the closest subroutine context above $from.
+ my $num = sub {
+ my @a = ('a' .. 'z');
+ unwind +(want_at(HERE) ? @a : scalar @a) => HERE;
+ # not reached
+ }->();
- "EVAL $from"
- The level of the closest eval context above $from.
+ will rightfully set $num to 26.
- If $from is omitted in any of those functions, the current level is used
- as the reference level.
+CONSTANTS
+ "SU_THREADSAFE"
+ True iff the module could have been built when thread-safety features.
- "CALLER $stack"
- The level corresponding to the stack referenced by "caller $stack".
+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", "DOWN", "SUB", "EVAL" and
+ The constant "SU_THREADSAFE" is also only exported on request,
+ individually or by the tags ':consts' 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'.
local $x = 0;
{
- reap sub { print $x } => 0;
+ reap sub { print $x } => HERE;
local $x = 1;
...
}
...
{
local $x = 1;
- reap sub { $x = 2 } => 0;
+ 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".
- "reap", "localize" and "localize_elem" effects 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
+ 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.
+ Continuation::Escape is a thin wrapper around Scope::Upper that gives
+ you a continuation passing style interface to "unwind". It's easier to
+ use, but it requires you to have control over the scope where you want
+ to return.
+
AUTHOR
Vincent Pit, "<perl at profvince.com>", <http://www.profvince.com>.
ACKNOWLEDGEMENTS
Inspired by Ricardo Signes.
+ Thanks to Shawn M. Moore for motivation.
+
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