package Scope::Guard;

use strict;
use warnings;

use Carp qw(confess);
use Exporter ();

our @ISA = qw(Exporter);
our @EXPORT_OK = qw(guard scope_guard);
our $VERSION = '0.20';

sub new {
    confess "Can't create a Scope::Guard in void context" unless (defined wantarray);

    my $class = shift;
    my $handler = shift() || die 'Scope::Guard::new: no handler supplied';
    my $ref = ref $handler || '';

    die "Scope::Guard::new: invalid handler - expected CODE ref, got: '$ref'"
        unless (UNIVERSAL::isa($handler, 'CODE'));

    bless [ 0, $handler ], ref $class || $class;
}

sub dismiss {
    my $self = shift;
    my $dismiss = @_ ? shift : 1;

    $self->[0] = $dismiss;
}

sub guard(&) { __PACKAGE__->new(shift) }
sub scope_guard($) { __PACKAGE__->new(shift) }

sub DESTROY {
    my $self = shift;
    my ($dismiss, $handler) = @$self;

    $handler->() unless ($dismiss);
}

1;

__END__

=pod

=head1 NAME

Scope::Guard - lexically-scoped resource management

=head1 SYNOPSIS

    my $guard = guard { ... };

      # or

    my $guard = scope_guard \&handler;

      # or

    my $guard = Scope::Guard->new(sub { ... });

    $guard->dismiss(); # disable the handler

=head1 DESCRIPTION

This module provides a convenient way to perform cleanup or other forms of resource
management at the end of a scope. It is particularly useful when dealing with exceptions:
the C<Scope::Guard> constructor takes a reference to a subroutine that is guaranteed to
be called even if the thread of execution is aborted prematurely. This effectively allows
lexically-scoped "promises" to be made that are automatically honoured by perl's garbage
collector.

For more information, see: L<http://www.drdobbs.com/cpp/184403758>

=head1 METHODS

=head2 new

    my $guard = Scope::Guard->new(sub { ... });

      # or

    my $guard = Scope::Guard->new(\&handler);

The C<new> method creates a new C<Scope::Guard> object which calls the supplied handler when its C<DESTROY> method is
called, typically at the end of the scope.

=head2 dismiss

    $guard->dismiss();

      # or

    $guard->dismiss(1);

C<dismiss> detaches the handler from the C<Scope::Guard> object. This revokes the "promise" to call the
handler when the object is destroyed.

The handler can be re-enabled by calling:

    $guard->dismiss(0);

=head1 EXPORTS

=head2 guard

C<guard> takes a block and returns a new C<Scope::Guard> object. It can be used
as a shorthand for:

    Scope::Guard->new(...)

e.g.

    my $guard = guard { ... };
    
Note: calling C<guard> anonymously, i.e. in void context, will raise an exception.
This is because anonymous guards are destroyed B<immediately>
(rather than at the end of the scope), which is unlikely to be the desired behaviour.

=head2 scope_guard

C<scope_guard> is the same as C<guard>, but it takes a code ref rather than a block.
e.g.

    my $guard = scope_guard \&handler;

or:

    my $guard = scope_guard sub { ... };

or:

    my $guard = scope_guard $handler;

As with C<guard>, calling C<scope_guard> in void context will raise an exception.

=head1 VERSION

0.20

=head1 SEE ALSO

=over

=item * L<B::Hooks::EndOfScope|B::Hooks::EndOfScope>

=item * L<End|End>

=item * L<Guard|Guard>

=item * L<Hook::Scope|Hook::Scope>

=item * L<Object::Destroyer|Object::Destroyer>

=item * L<Perl::AtEndOfScope|Perl::AtEndOfScope>

=item * L<ReleaseAction|ReleaseAction>

=item * L<Scope::local_OnExit|Scope::local_OnExit>

=item * L<Scope::OnExit|Scope::OnExit>

=item * L<Sub::ScopeFinalizer|Sub::ScopeFinalizer>

=item * L<Value::Canary|Value::Canary>

=back

=head1 AUTHOR

chocolateboy <chocolate@cpan.org>

=head1 COPYRIGHT

Copyright (c) 2005-2010, chocolateboy.

This module is free software. It may be used, redistributed and/or modified under the same terms
as Perl itself.

=cut
