From @ikegami

Hi,

Given a tied hash that contains a value which is an object with overloads,
the following code attempts to numify the overloaded object​:

  $tied_hash{overloaded_object} += 3;

The overloaded '+=' isn't getting called. The following works fine​:

  $tied_hash{overloaded_object} = $tied_hash{overloaded_object} + 3;
  $plain_hash{overloaded_object} = $plain_hash{overloaded_object} + 3;
  $plain_hash{overloaded_object} += 3;

Tested with v5.12.2 and a recent blead (v5.13.9-284-g76cc22e).

Test case and output below.

- Eric Brine

----- BEGIN CODE -----
#!/usr/bin/env perl

use strict;
use warnings;

{
  package Test;

  use overload
  '+' => \&append,
  '+=' => \&append;

  sub append {
  my ( $self, $value ) = @​_;
  push @​$self, $value;
  return $self;
  }
}

use Test​::More tests => 3;

use Tie​::Hash qw( );

{ # Works for "+" instead of "+=".
  my %hash;
  tie %hash, 'Tie​::StdHash';
  $hash{'test'} = bless [], 'Test';

  eval { $hash{'test'} = $hash{'test'} + 3; 1 }
  or diag("$@​");

  is(3, $hash{'test'}[0], '+, tied hash');
}

{ # Works for untied hash, so it's not a problem with the overloaded object.
  my %hash;
  $hash{'test'} = bless [], 'Test';

  eval { $hash{'test'} += 3; 1 }
  or diag("$@​");

  is(3, $hash{'test'}[0], '+=, normal hash');
}

{
  my %hash;
  tie %hash, 'Tie​::StdHash';
  $hash{'test'} = bless [], 'Test';

  eval { $hash{'test'} += 3; 1 }
  or diag("$@​");

  is(3, $hash{'test'}[0], '+=, tied hash');
}
----- END CODE -----

----- BEGIN OUTPUT -----
1..3
ok 1 - +, tied hash
ok 2 - +=, normal hash
# Operation "0+"​: no method found, argument in overloaded package Test at
a.pl line 50.
not ok 3 - +=, tied hash
# Failed test '+=, tied hash'
# at a.pl line 53.
# got​: '3'
# expected​: undef
# Looks like you failed 1 test of 3.
----- END OUTPUT -----

From @iabyn

On Wed, Feb 23, 2011 at 01​:09​:06PM -0800, Eric Brine wrote​:

Given a tied hash that contains a value which is an object with overloads,
the following code attempts to numify the overloaded object​:

$tied\_hash\{overloaded\_object\} \+= 3;

The overloaded '+=' isn't getting called. The following works fine​:

$tied\_hash\{overloaded\_object\} = $tied\_hash\{overloaded\_object\} \+ 3;
$plain\_hash\{overloaded\_object\} = $plain\_hash\{overloaded\_object\} \+ 3;
$plain\_hash\{overloaded\_object\} \+= 3;

Tested with v5.12.2 and a recent blead (v5.13.9-284-g76cc22e).

Test case and output below.

- Eric Brine

----- BEGIN CODE -----
#!/usr/bin/env perl

use strict;
use warnings;

{
package Test;

use overload
   '\+'  => \\&append\,
   '\+=' => \\&append;

sub append \{
    my \( $self\, $value \) = @​\_;
    push @​$self\, $value;
    return $self;
\}

}

use Test​::More tests => 3;

use Tie​::Hash qw( );

{ # Works for "+" instead of "+=".
my %hash;
tie %hash, 'Tie​::StdHash';
$hash{'test'} = bless [], 'Test';

eval \{ $hash\{'test'\} = $hash\{'test'\} \+ 3; 1 \}
    or diag\("$@​"\);

is\(3\, $hash\{'test'\}\[0\]\, '\+\, tied hash'\);

}

{ # Works for untied hash, so it's not a problem with the overloaded object.
my %hash;
$hash{'test'} = bless [], 'Test';

eval \{ $hash\{'test'\} \+= 3; 1 \}
    or diag\("$@​"\);

is\(3\, $hash\{'test'\}\[0\]\, '\+=\, normal hash'\);

}

{
my %hash;
tie %hash, 'Tie​::StdHash';
$hash{'test'} = bless [], 'Test';

eval \{ $hash\{'test'\} \+= 3; 1 \}
    or diag\("$@​"\);

is\(3\, $hash\{'test'\}\[0\]\, '\+=\, tied hash'\);

}
----- END CODE -----

----- BEGIN OUTPUT -----
1..3
ok 1 - +, tied hash
ok 2 - +=, normal hash
# Operation "0+"​: no method found, argument in overloaded package Test at
a.pl line 50.
not ok 3 - +=, tied hash
# Failed test '+=, tied hash'
# at a.pl line 53.
# got​: '3'
# expected​: undef
# Looks like you failed 1 test of 3.
----- END OUTPUT -----

This was fixed in a recent blead. Under blead, you get instead​:

ok 1 - +, tied hash
ok 2 - +=, normal hash
# Operation "="​: no method found, argument in overloaded package Test at /tmp/p line 52.
...

because with a tie, it can't determine whether its safe to skip using the
copy constructor, so it always calls it. Adding one, e.g.

  '=' => sub { bless [ @​{$_[0]} ], 'Test' },

makes all three tests pass.

--
Any [programming] language that doesn't occasionally surprise the
novice will pay for it by continually surprising the expert.
  -- Larry Wall

The RT System itself - Status changed from 'new' to 'open'

@iabyn - Status changed from 'open' to 'resolved'