calling overloaded comparison operators as method calls?

perl5ever has asked for the wisdom of the Perl Monks concerning the following question:

Is there a way to reliably call operators such as eq, ne, etc. on an object which you know has those operators overloaded? However, I don't want to make assumptions about the class of the object.

Here's an example:

sub create_selector {
  my ($spec) = @_;
  my $selector;
  if ($spec =~ m/^=(.*)/) {
    $selector = sub { $_[0]->version eq $1 }
  } elsif ($spec =~ m/!=(.*)/) {
    $selector = sub { $_[0]->version ne $1 }
  } elsif ($spec =~ m/>(.*)/) {
    $selector = sub { $_[0]->version gt $1 }
  }
  $selector;
}

my $selector = create_selector("=6.2");
...
my @selected_dists = grep { $selector->{$_} } @list_of_dists;
[download]

The idea is that I could write create_selector like this:

sub create_selector {
  my ($spec) = @_;
  my $selector;
  if ($spec =~ m/^(=|!=|<|>)(.*)/) {
    my $op = $1;
    my $method = ...translate $op to a method name...
    $selector = sub { $_[0]->version->$method($2) }
  }
}
[download]

That is, I want to be able to perform the translation of $op to a method name in a way which will work for whatever object I'll be applying it to.

Comment on calling overloaded comparison operators as method calls? Select or Download Code

Replies are listed 'Best First'.
Re: calling overloaded comparison operators as method calls? by morgon (Priest) on Jul 05, 2009 at 20:32 UTC
I am not sure if I understand your problem. If you make your selector like this: `my $selector = sub { $_[0] eq $whatever };` [download] Then you can call it with any object as $selector->($object) (parentheses - not curly braces to call it!) and it will either use the built-in eq or the overloaded version. As far as I understand you that is what you want which is why I probably don't understand you... But as an aside you can get a reference to the overloading method with overload::Method, so if you really wanted you could to something like (for the "eq"-case) `my $selector = sub { my($obj)=@_; my $code_ref = overload::Method($obj, "eq"); if($code_ref) { # $obj overloads "eq" # call the overloading-implementation return $code_ref->($obj, $whatever); else { # no overloading -do something else return $obj eq $whatever; } };` [download]	[reply] [d/l] [select]
Re^2: calling overloaded comparison operators as method calls? by perl5ever (Pilgrim) on Jul 05, 2009 at 20:47 UTC
What I want is the `overload::Method` function. That way I don't have to write separate conditionals for each operation. Thanks!	[reply] [d/l]
Re^3: calling overloaded comparison operators as method calls? by morgon (Priest) on Jul 06, 2009 at 09:56 UTC
btw: All of that is covered in the manpage (perldoc overload) - rtfm :-)	[reply]