Scope::Upper - Act on upper scopes.
VERSION
- Version 0.10
+ Version 0.11
SYNOPSIS
- package X;
+ "reap", "localize", "localize_elem", "localize_delete" and "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..."
- package Z;
+ {
+ 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"
+
+ "unwind" and "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
DESCRIPTION
This module lets you defer actions *at run-time* that will take place
needed, and it will still denote the original scope.
"reap $callback, $context"
- Add a destructor that calls $callback (in void context) when the upper
+ Adds a destructor that calls $callback (in void context) 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 :
+ Introduces 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 = $value". For
corresponding type.
When the symbol is given by a string, it is resolved when the actual
- localization takes place and not when "localize" is called. This
- means that
-
- sub tag { localize '$x', $_[0] => UP }
-
- will localize in the caller's namespace.
+ localization takes place and not when "localize" is called. Thus, if
+ the symbol name is not qualified, it will refer to the variable in
+ the package where the localization actually takes place and not in
+ the one where the "localize" call was compiled. For example,
+
+ {
+ package Scope;
+ sub new { localize '$tag', $_[0] => UP }
+ }
+
+ {
+ package Tool;
+ {
+ Scope->new;
+ ...
+ }
+ }
+
+ will localize $Tool::tag and not $Scope::tag. If you want the other
+ behaviour, you just have to specify $what as a glob or a qualified
+ name.
+
+ Note that if $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 "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.
"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.
+ Introduces a "local $what[$key] = $value" or "local $what{$key} =
+ $value" delayed to the time of first return into the upper scope denoted
+ by $context. Unlike "localize", $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, "localize_elem" will throw
+ an exception. $key is either an array index or a hash key, depending of
+ which kind of variable you localize.
+
+ If $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.
"localize_delete $what, $key, $context"
- Similiar to "localize", but for deleting variables or array/hash
- elements. $what can be:
+ Introduces the deletion of a variable or an array/hash element delayed
+ to the time of first return into the upper scope denoted by $context.
+ $what can be:
* A glob, in which case $key is ignored and the call is equivalent to
"local *x".
"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.
+ subroutine, eval or format at or just above $context, and immediately
+ restart the program flow at this point - thus effectively returning to
+ an upper scope.
The upper context isn't coerced onto @values, which is hence always
evaluated in list context. This means that
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
+ Like "wantarray", but for the subroutine/eval/format at or just above
$context.
The previous example can then be "corrected" :
XSLoader (standard since perl 5.006).
SEE ALSO
+ "local" in perlfunc, "Temporary Values via local()" in perlsub.
+
Alias, Hook::Scope, Scope::Guard, Guard.
Continuation::Escape is a thin wrapper around Scope::Upper that gives
use, but it requires you to have control over the scope where you want
to return.
+ Scope::Escape.
+
AUTHOR
Vincent Pit, "<perl at profvince.com>", <http://www.profvince.com>.
projects / perl / modules / Scope-Upper.git / commitdiff