I'd like to be able to write something like the following...
call_with_scope({
x => 47,
}, sub {
printf "$x\n";
printf "$y\n";
});
Where $y is bound in the environment containing the expression (either lexically or dynamically depending on the symbol).
I've found a way to do it, but it requires no strict "vars" to be in effect in the expression containing call_with_scope(...) and the implementation of call_with_scope uses eval to create local bindings before transferring control to the callback.
Is there a way to avoid either requiring no strict "vars" at the call site or refer to and change the value of a local variable without resorting to eval?
For completeness, the code snippet below implements call_with_scope and prints 47 and then 48.
#!/usr/bin/env perl
use strict;
use warnings;
sub call_with_scope {
my ($env, $func) = #_;
my %property;
my #preamble;
foreach my $k (keys %$env) {
$property{$k} = $env->{$k};
# deliberately omitted: logic to ensure that ${$k} is a well-formed variable
push #preamble, "local \$$k = \$property{'$k'};";
}
# force scalar context
do {
my $str = join('', 'no strict "vars";', #preamble, '$_[1]->();');
return scalar(eval($str));
};
}
do {
no strict 'vars';
local $x;
my $y = 48;
call_with_scope(
{
x => 47,
},
sub {
printf "$x\n";
printf "$y\n";
}
);
};
I'm trying to write something kind of like Test::LectroTest ... except that instead of using a source filter and comments like in Property { ##[ x <- Int, y <- Int ]## <body> } ... I want to write something like Property({x => gen_int, y => gen_int}, sub { <body> }) where $x and $y inside body get their values when an "instantiation" of a property test is performed.
You can do this by defining $x and $y as globals in the caller's package.
no strict 'refs';
my $caller = caller;
for my $var (keys %$properties) {
*{$caller.'::'.$var} = $properties->{$var};
}
$code->();
But this can't be easily localized. And polluting the caller's namespace with globals potentially leads to mysterious data leaking between tests. In general, use as little magic as possible in a test library; the user will have enough of their own weird magic to debug.
Instead, provide a function which returns the properties. For example, p.
package LectroTest;
use Exporter qw(import);
our #EXPORT = qw(test p);
our $P;
sub test {
my($props, $test) = #_;
local $P = $props;
$test->();
}
sub p {
return $P;
}
And the test looks like:
use LectroTest;
test(
{ x => 42 }, sub { print p->{x} }
);
The problem is that the anon sub is compiled before call_with_scope is called, so there's no chance for call_with_scope to declare variables for that sub.
Any reason you're not using arguments like any other sub?
call_with_scope([ 47 ], sub {
my ($x) = #_;
printf "%s\n", $x;
printf "%s\n", $y;
});
It's not any longer!
Here's an alternative if you're ok in declaring $x outside of the sub.
use strict;
use warnings;
use PadWalker qw( closed_over );
sub call_with_scope {
my ($inits, $cb) = #_;
my $captures = closed_over($cb);
for my $var_name_with_sigil (keys(%$captures)) {
my ($var_name) = $var_name_with_sigil =~ /^\$(.*)/s
or next;
$inits->{$var_name}
or next;
${ $captures->{$var_name_with_sigil} } = $inits->{$var_name};
}
return $cb->();
}
{
my $x;
my $y = 48;
call_with_scope({
x => 47,
}, sub {
printf "%s\n", $x;
printf "%s\n", $y;
});
}
This works because variables are created at compile-time and cleared on scope exit.
It even works if sub was compiled in a different scope and package than the call to call_with_scope.
{
my $sub = do {
my $x;
my $y = 48;
sub {
printf "%s\n", $x;
printf "%s\n", $y;
}
};
call_with_scope({ x => 47 }, $sub);
}
But do you really want that kind of magic in your program?
Related
I'd like to weaken captured variables in the code generated by Sub::Quote. For example, here's the non-quoted alternative:
use 5.10.0;
use Scalar::Util qw[ weaken ];
{
my $s = 'foo';
my $x = sub { say $s };
weaken( my $y = $x );
my $bar = sub { &$y };
&$bar;
$x = undef;
&$bar
}
and the output:
foo
Can't use an undefined value as a subroutine reference [...]
And here's my Sub::Quote attempt:
use 5.10.0;
use Sub::Quote;
use Scalar::Util qw[ weaken ];
{
my $s = 'foo';
my $x = sub { say $s };
weaken( my $y = $x );
my $bar = quote_sub( '&$y', { '$y' => \$y } );
&$bar;
$x = undef;
&$bar;
}
and the output:
foo
foo
Obviously the captured $y isn't weakened. Is there a way of altering the generated code to weaken captured variables?
The documentation is sparse, and the Sub::Quote implementation is complex; I'm fairly convinced this isn't possible with the current code, but I'd love to be shown to be wrong.
my $bar = quote_sub( '&$y', { '$y' => \$y } );
is roughly the same as
my $bar = eval(q{ my $y = $y; sub { &$y } });
(It does more, but those bits are irrelevant to this question). As you can see, that creates a new strong reference to the sub[1].
As a workaround, you could add a layer of indirection:
my $bar = eval(q{ my $y_ref = \$y; sub { &{ $$y_ref } } });
This can be achieved by using:
my $bar = quote_sub( '&{$$y_ref}', { '$y_ref' => \\$y } );
There wouldn't be any problems if the $y created by Sub::Quote was an alias for your $y. This can be achieved using Data::Alias or an experimental feature introduced in 5.22.
This can be demonstrated using the following:
{
package Sub::Quote;
my $sub = sub {
my ($from, $captures, $indent) = #_;
join(
'',
"use feature qw( refaliasing );\n",
"no warnings qw( experimental::refaliasing );\n",
map {
/^([\#\%\$])/
or croak "capture key should start with \#, \% or \$: $_";
(' ' x $indent).qq{\\my ${_} = \\${1}{${from}->{${\quotify $_}}};\n};
} keys %$captures
)
};
no warnings qw( redefine );
*capture_unroll = $sub;
}
my $bar = quote_sub( '&$y', { '$y' => \$y } );
You could talk to the module's maintainer about adding an option that would cause the use of aliasing.
When you create a copy of a (strong or weak) reference, it's a strong reference.
In Perl, when one uses the sort function with a custom comparison, the variables $a and $b are already assigned to the current pair of elements to compare, e.g. in:
#decreasing = sort { $b <=> $a } #list;
How can I write other subroutines with a similar functionality? For example, imagine that I want to write sort of process_and_store function that does something special with each item of a list and then stores it in a database; and where the variable $item is already assigned to the current item being processed. I would like to write for example something like:
process_and_store { do_something_with($item); } #list;
Rather than
process_and_store { my $item = shift; do_something_with($item); } #list;
How should I go about doing this?
UPDATE: For completeness, although flesk's answer works without problems, in order to “properly” localize the changes I make to the $item variable I had to follow the advice from Axeman. In SomePackage.pm I placed something like:
package SomePackage;
use strict;
require Exporter;
our #ISA = qw/Exporter/;
our #EXPORT = qw(process_and_store);
our $item;
sub import {
my $import_caller = caller();
{ no strict 'refs';
*{ $import_caller . '::item' } = \*item;
}
# Now, cue Exporter!
goto &{ Exporter->can( 'import' ) };
}
sub process_and_store (&#) {
my $code = shift;
for my $x (#_) {
local *item = \$x;
$code->();
print "stored: $item\n"
}
}
1;
Then I call this from main.pl with something like:
#!/usr/bin/perl -w
use strict;
use SomePackage;
process_and_store { print "seen: $item\n"; } (1, 2, 3);
And get the expected result:
seen: 1
stored: 1
seen: 2
stored: 2
seen: 3
stored: 3
In my "associative array" processing library, I do something similar. The user can export the variables $k and $v (key-value) so that they can do things like this:
each_pair { "$k => $v" } some_source_list()
Here's how I do it:
I declare our ( $k, $v ) in the implementing package.
In import I allow packages to export those symbols and alias them in the
receiving package: *{$import_caller.'::'.$name} = \*{ $name };
In the pair processors, I do the following:
local *::_ = \$_[0];
local *k = \$_[0];
local *v = \$_[1];
#res = $block->( $_[0], $_[1] );
Thus $k and $v are aliases of what's in the queue. If this doesn't have to be the case, then you might be happy enough with something like the following:
local ( $k, $v ) = splice( #_, 0, 2 );
local $_ = $k;
But modifiable copies also allow me to do things like:
each_pair { substr( $k, 0, 1 ) eq '-' and $v++ } %some_hash;
UPDATE:
It seems that you're neglecting step #2. You have to make sure that the symbol in the client package maps to your symbol. It can be as simple as:
our $item;
sub import {
my $import_caller = caller();
{ no strict 'refs';
*{ $import_caller . '::item' } = \*item;
}
# Now, cue Exporter!
goto &{ Exporter->can( 'import' ) };
}
Then when you localize your own symbol, the aliased symbol in the client package is localized as well.
The main way that I can see that it would work without the local, is if you were calling it from the same package. Otherwise, $SomePackage::item and $ClientPackage::item are two distinct things.
I think it's a bit of a hack, but you could do something like this:
#!/usr/bin/perl
use strict;
use warnings;
my $item;
sub process_and_store(&#) {
my $code = shift;
for (#_) {
$item = $_;
&$code();
}
undef $item;
}
The thing is, $item has to be a global scalar for this to work, so process_and_store has to update that scalar while looping over the list. You should also undef $item at the end of the sub routine to limit any potential side-effects. If I were to write something like this, I'd tuck it away in a module and make it possible to define the iterator variable, so as to limit name conflicts.
Test:
my #list = qw(apples pears bananas);
process_and_store { do_something_with($item) } #list;
sub do_something_with {
my $fruit = shift;
print "$fruit\n";
}
Output:
apples
pears
bananas
The $a and $b variables are special in Perl; they're real global variables and hence exempt from use strict, and also used specifically by the sort() function.
Most other similar uses in Perl would use the $_ global for this sort of thing:
process_and_store { do_something_with( $_ ) } #list;
Which is already handled by the normal $_ rules. Don't forget to localise $_:
sub process_and_store(&#)
{
my $code = shift;
foreach my $item (#_) {
local $_ = $item;
$code->();
}
}
I want to call a main controller function that dispatches other function dynamically, something like this:
package Controller;
my %callback_funcs = ();
sub register_callback{
my ($class,$callback,$options) = _#;
#apppend to %callback_funcs hash ... ?
}
sub main{
%callback_funcs = ( add => 'add_func', rem => 'remove_func', edit => 'edit_func');
while(<STDIN>){
last if ($_ =~ /^\s*$/);
if($_ == 'add' || _$ == 'rem' || _$ == 'edit'){
$result = ${callback_funcs['add']['func']}(callback_funcs['add']['options']);
}
}
}
sub add_func{
...
}
One caveat is that the subs are defined in other Modules, so the callbacks would have to be able to reference them... plus
I'm having a hard time getting the hashes right!
So, it's possible to have a hash that contains anonymous subroutines that you can invoke from stdin.
my %callbacks = (
add => sub {
# do stuff
},
fuzzerbligh => sub {
# other stuff
},
);
And you can insert more hashvalues into the hash:
$callbacks{next} = sub {
...
};
And you would invoke one like this
$callbacks{next}->(#args);
Or
my $coderef = $callbacks{next};
$coderef->(#args);
You can get the hashkey from STDIN, or anywhere else.
You can also define them nonymously and then take a reference to them.
sub delete {
# regular sub definition
}
$callbacks{delete} = \&delete;
I wouldn't call these callbacks, however. Callbacks are subs that get called after another subroutine has returned.
Your code is also rife with syntax errors which may be obscuring the deeper issues here. It's also not clear to me what you're trying to do with the second level of arrays. When are you defining these subs, and who is using them when, and for what?
Perhaps this simplified example will help:
# Very important.
use strict;
use warnings;
# Define some functions.
sub multiply { $_[0] * $_[1] }
sub divide { $_[0] / $_[1] }
sub add { $_[0] + $_[1] }
sub subtract { $_[0] - $_[1] }
# Create a hash of references to those functions (dispatch table).
my %funcs = (
multiply => \&multiply,
divide => \÷,
add => \&add,
subtract => \&subtract,
);
# Register some more functions.
sub register {
my ($key, $func) = #_;
$funcs{$key} = $func;
}
register('+', \&add); # As above.
register('sum', sub { # Or using an anonymous subroutine.
my $s = 0;
$s += $_ for #_;
return $s;
});
# Invoke them dynamically.
while (<>){
my ($op, #args) = split;
last unless $op and exists $funcs{$op}; # No need for equality tests.
print $funcs{$op}->(#args), "\n";
}
You've already got some good answers on how to build a dispatch table and call functions through it within a single file, but you also keep talking about wanting the functions to be defined in other modules. If that's the case, then wouldn't it be better to build the dispatch table dynamically based on what dispatchable functions each module says it has rather than having to worry about keeping it up to date manually? Of course it would!
Demonstrating this requires multiple files, of course, and I'm using Module::Pluggable from CPAN to find the modules which provide the function definitions.
dispatch_core.pl:
#!/usr/bin/env perl
use strict;
use warnings;
my %dispatch;
use lib '.'; # a demo is easier if I can put modules in the same directory
use Module::Pluggable require => 1, search_path => 'DTable';
for my $plugin (plugins) {
%dispatch = (%dispatch, $plugin->dispatchable);
}
for my $func (sort keys %dispatch) {
print "$func:\n";
$dispatch{$func}->(2, 5);
}
DTable/Add.pm:
package DTable::Add;
use strict;
use warnings;
sub dispatchable {
return (add => \&add);
}
sub add {
my ($num1, $num2) = #_;
print "$num1 + $num2 = ", $num1 + $num2, "\n";
}
1;
DTable/MultDiv.pm:
package DTable::MultDiv;
use strict;
use warnings;
sub dispatchable {
return (multiply => \&multiply, divide => \÷);
}
sub multiply {
my ($num1, $num2) = #_;
print "$num1 * $num2 = ", $num1 * $num2, "\n";
}
sub divide {
my ($num1, $num2) = #_;
print "$num1 / $num2 = ", $num1 / $num2, "\n";
}
1;
Then, on the command line:
$ ./dispatch_core.pl
add:
2 + 5 = 7
divide:
2 / 5 = 0.4
multiply:
2 * 5 = 10
Adding new functions is now as simple as dropping a new file into the DTable directory with an appropriate dispatchable sub. No need to ever touch dispatch_core.pl just to add a new function again.
Edit: In response to the comment's question about whether this can be done without Module::Pluggable, here's a modified dispatch_core.pl which doesn't use any external modules other than the ones defining the dispatchable functions:
#!/usr/bin/env perl
use strict;
use warnings;
my %dispatch;
my #dtable = qw(
DTable::Add
DTable::MultDiv
);
use lib '.';
for my $plugin (#dtable) {
eval "use $plugin";
%dispatch = (%dispatch, $plugin->dispatchable);
}
for my $func (sort keys %dispatch) {
print "$func:\n";
$dispatch{$func}->(2, 5);
}
I am writing a module and I want a specific piece of code to be executed before each of the functions in it.
How do I do that?
Is there no other way than to just have a function-call at the beginning of every function?
You can do this in Moose with method modifiers:
package Example;
use Moose;
sub foo {
print "foo\n";
}
before 'foo' => sub { print "about to call foo\n"; };
Wrapping a method is also possible with method attributes, but this route is not well-used in Perl and is still evolving, so I wouldn't recommend it. For normal use-cases, I would simply put the common code in another method and call it at the top of each of your functions:
Package MyApp::Foo;
sub do_common_stuff { ... }
sub method_one
{
my ($this, #args) = #_;
$this->do_common_stuff();
# ...
}
sub method_two
{
my ($this, #args) = #_;
$this->do_common_stuff();
# ...
}
And, in case someone is wondering how to achieve the effect of Hook* modules or Moose's "before" explicitly (e.g. what actual Perl mechanism can be used to do it), here's an example:
use strict;
package foo;
sub call_before { print "BEFORE\n"; } # This will be called before any sub
my $call_after = sub { print "AFTER - $_[0]\n"; };
sub fooBar { print "fooBar body\n\n"; }
sub fooBaz { print "fooBaz body\n\n"; }
no strict; # Wonder if we can get away without 'no strict'? Hate doing that!
foreach my $glob (keys %foo::) { # Iterate over symbol table of the package
next if not defined *{$foo::{$glob}}{CODE}; # Only subroutines needed
next if $glob eq "call_before" || $glob eq "import" || $glob =~ /^___OLD_/;
*{"foo::___OLD_$glob"} = \&{"foo::$glob"}; # Save original sub reference
*{"foo::$glob"} = sub {
call_before(#_); &{"foo::___OLD_$glob"}(#_); &$call_after(#_);
};
}
use strict;
1;
package main;
foo::fooBar();
foo::fooBaz();
The explanation for what we're excluding via "next" line:
"call_before" is of course the name I gave to our "before" example sub - only need this if it is actually defined as a real sub in the same package and not anonymously or code ref from outside the package.
import() has a special meaning and purpose and should generally be excluded from "run this before every sub" scenario. YMMV.
___OLD_ is a prefix we will give to "renamed" old subs - you don't need to include it here unless you're worried about this loop being execute twice. Better safe than sorry.
UPDATE: Below section about generalization is no longer relevant - at the end of the answer I pasted a general "before_after" package doing just that!!!
The loop above can obviously be easily generalized to be a separately-packaged subroutine which accepts, as arguments:
an arbitrary package
a code ref to arbitrary "before" subroutine (or as you can see, after)
and a list of sub names to exclude (or sub ref that checks if a name is to be excluded) aside from standard ones like "import").
... and/or a list of sub names to include (or sub ref that checks if a name is to be included) aside from standard ones like "import"). Mine just takes ALL subs in a package.
NOTE: I don't know whether Moose's "before" does it just this way. What I do know is that I'd obviously recommend going with a standard CPAN module than my own just-written snippet, unless:
Moose or any of the Hook modules can't be installed and/or are too heavy weight for you
You're good enough with Perl that you can read the code above and analyze it for flaws.
You like this code very much, AND the risk of using it over CPAN stuff is low IYHO :)
I supplied it more for informational "this is how the underlying work is done" purposes rather than practical "use this in your codebase" purposes, though feel free to use it if you wish :)
UPDATE
Here's a more generic version as mentioned before:
#######################################################################
package before_after;
# Generic inserter of before/after wrapper code to all subs in any package.
# See below package "foo" for example of how to use.
my $default_prefix = "___OLD_";
my %used_prefixes = (); # To prevent multiple calls from stepping on each other
sub insert_before_after {
my ($package, $prefix, $before_code, $after_code
, $before_filter, $after_filter) = #_;
# filters are subs taking 2 args - subroutine name and package name.
# How the heck do I get the caller package without import() for a defalut?
$prefix ||= $default_prefix; # Also, default $before/after to sub {} ?
while ($used_prefixes{$prefix}) { $prefix = "_$prefix"; }; # Uniqueness
no strict;
foreach my $glob (keys %{$package . "::"}) {
next if not defined *{$package. "::$glob"}{CODE};
next if $glob =~ /import|__ANON__|BEGIN/; # Any otrher standard subs?
next if $glob =~ /^$prefix/; # Already done.
$before = (ref($before_filter) ne "CODE"
|| &$before_filter($glob, $package));
$after = (ref($after_filter) ne "CODE"
|| &$after_filter($glob, $package));
*{$package."::$prefix$glob"} = \&{$package . "::$glob"};
if ($before && $after) { # We do these ifs for performance gain only.
# Else, could wrap before/after calls in "if"
*{$package."::$glob"} = sub {
my $retval;
&$before_code(#_); # We don't save returns from before/after.
if (wantarray) {
$retval = [ &{$package . "::$prefix$glob"}(#_) ];
} else {
$retval = &{$package . "::$prefix$glob"}(#_);
}
&$after_code(#_);
return (wantarray && ref $retval eq 'ARRAY')
? #$retval : $retval;
};
} elsif ($before && !$after) {
*{$package . "::$glob"} = sub {
&$before_code(#_);
&{$package . "::$prefix$glob"}(#_);
};
} elsif (!$before && $after) {
*{$package . "::$glob"} = sub {
my $retval;
if (wantarray) {
$retval = [ &{$package . "::$prefix$glob"}(#_) ];
} else {
$retval = &{$package . "::$prefix$glob"}(#_);
}
&$after_code(#_);
return (wantarray && ref $retval eq 'ARRAY')
? #$retval : $retval;
};
}
}
use strict;
}
# May be add import() that calls insert_before_after()?
# The caller will just need "use before_after qq(args)".
1;
#######################################################################
package foo;
use strict;
sub call_before { print "BEFORE - $_[0]\n"; };
my $call_after = sub { print "AFTER - $_[0]\n"; };
sub fooBar { print "fooBar body - $_[0]\n\n"; };
sub fooBaz { print "fooBaz body - $_[0]\n\n"; };
sub fooBazNoB { print "fooBazNoB body - $_[0]\n\n"; };
sub fooBazNoA { print "fooBazNoA body - $_[0]\n\n"; };
sub fooBazNoBNoA { print "fooBazNoBNoA body - $_[0]\n\n"; };
before_after::insert_before_after(__PACKAGE__, undef
, \&call_before, $call_after
, sub { return 0 if $_[0] eq "call_before"; $_[0] !~ /NoB(NoA)?$/ }
, sub { return 0 if $_[0] eq "call_before"; $_[0] !~ /NoA$/ } );
1;
#######################################################################
package main;
use strict;
foo::fooBar("ARG1");
foo::fooBaz("ARG2");
foo::fooBazNoB("ARG3");
foo::fooBazNoA("ARG4");
foo::fooBazNoBNoA("ARG5");
#######################################################################
If you search CPAN for 'hook', and then branch out from there, you'll find several options, such as:
Hook::WrapSub
Hook::PrePostCall
Hook::LexWrap
Sub::Prepend
Here's an example using Hook::LexWrap. I don't have experience with this module except for debugging. It worked fine for that purpose.
# In Frob.pm
package Frob;
sub new { bless {}, shift }
sub foo { print "foo()\n" }
sub bar { print "bar()\n" }
sub pre { print "pre()\n" }
use Hook::LexWrap qw(wrap);
my #wrappable_methods = qw(foo bar);
sub wrap_em {
wrap($_, pre => \&pre) for #wrappable_methods;
}
# In script.pl
use Frob;
my $frob = Frob->new;
print "\nOrig:\n";
$frob->foo;
$frob->bar;
print "\nWrapped:\n";
Frob->wrap_em();
$frob->foo;
$frob->bar;
See the Aspect package on CPAN for aspect-oriented computing.
before { Class->method; } qr/^Package::\w+$/;
I often find it useful to be able to schedule code to be executed upon leaving the current scope. In my previous life in TCL, a friend created a function we called defer.
It enabled code like:
set fp [open "x"]
defer("close $fp");
which was invoked when the current scope exited. The main benefit is that it's always invoked no matter how/where I leave scope.
So I implemented something similar in Perl but it seems there'd be an easier way. Comments critiques welcome.
The way I did it in Perl:
create a global, tied variable which holds an array of subs to be executed.
whenever I want to schedule a fn to be invoked on exit, I use local to change the array.
when I leave the current scope, Perl changes the global to the previous value
because the global is tied, I know when this value change happens and can invoke the subs in the list.
The actual code is below.
Is there a better way to do this? Seems this would be a commonly needed capability.
use strict;
package tiescalar;
sub TIESCALAR {
my $class = shift;
my $self = {};
bless $self, $class;
return $self;
}
sub FETCH {
my $self = shift;
return $self->{VAL};
}
sub STORE {
my $self = shift;
my $value = shift;
if (defined($self->{VAL}) && defined($value)) {
foreach my $s (#{$self->{VAL}}) { &$s; }
}
$self->{VAL} = $value;
}
1;
package main;
our $h;
tie($h, 'tiescalar');
$h = [];
printf "1\n";
printf "2\n";
sub main {
printf "3\n";
local $h = [sub{printf "9\n"}];
push(#$h, sub {printf "10\n";});
printf "4\n";
{
local $h = [sub {printf "8\n"; }];
mysub();
printf "7\n";
return;
}
}
sub mysub {
local $h = [sub {printf "6\n"; }];
print "5\n";
}
main();
printf "11\n";
Well, your specific case is already handled if you use lexical filehandles (as opposed to the old style bareword filehandles). For other cases, you could always use the DESTROY method of an object guaranteed to go to zero references when it goes out of scope:
#!/usr/bin/perl
use strict;
use warnings;
for my $i (1 .. 5) {
my $defer = Defer::Sub->new(sub { print "end\n" });
print "start\n$i\n";
}
package Defer::Sub;
use Carp;
sub new {
my $class = shift;
croak "$class requires a function to call\n" unless #_;
my $self = {
func => shift,
};
return bless $self, $class;
}
sub DESTROY {
my $self = shift;
$self->{func}();
}
ETA: I like brian's name better, Scope::OnExit is a much more descriptive name.
Instead of using tie for this, I think I'd just create an object. You can also avoid the local that way too.
{
my $defer = Scope::OnExit->new( #subs );
$defer->push( $other_sub ); # and pop, shift, etc
...
}
When the variable goes out of scope, you have a chance to do things in the DESTROY method.
Also, in the example you posted, you need to check that the values you store are code references, and it's probably a good idea to check that the VAL value is an array reference:
sub TIESCALAR { bless { VAL => [] }, $_[0] }
sub STORE {
my( $self, $value ) = #_;
carp "Can only store array references!" unless ref $value eq ref [];
foreach { #$value } {
carp "There should only be code refs in the array"
unless ref $_ eq ref sub {}
}
foreach ( #{ $self->{VAL}} ) { $_->() }
$self->{VAL} = $value;
}
You may want to try out B::Hooks::EndOfScope
I Believe this works:
use B::Hooks::EndOfScope;
sub foo {
on_scope_end {
$codehere;
};
$morecode
return 1; # scope end code executes.
}
foo();
I think you want something like Scope::Guard, but it can't be pushed. Hmmm.
Thanks.
Trivially,
sub OnLeavingScope::DESTROY { ${$_[0]}->() }
used like:
{
...
my $onleavingscope = bless \sub { ... }, 'OnLeavingScope';
my $onleavingscope2 = bless \\&whatever, 'OnLeavingScope';
...
}
(The extra level of having a reference to a reference to a sub is necessary only to work around an optimization (that's arguably a bug) when using a non-closure anonymous sub.)