From: Jos Backus <jos@...>
Date: 2006-08-11T10:33:57+09:00
Subject: Referring to an instance method using a variable

As part of a larger program I am trying to convert the following Perl code to
Ruby:

    lizzy:~% cat ptest
    sub equals {
	my($a, $b) = @_;
	return $a eq $b ? 1 : 0;
    }

    my $ops = {
	'=' => sub { my ($a, $b) = @_; return $a eq $b ? 1 : 0; },
	'==' => \&equals,
    };

    print $ops->{'='}(1, 1);
    print $ops->{'=='}(1, 2);
    lizzy:~% perl -l ptest
    1
    0
    lizzy:~% 

This is what I have come up with:

    lizzy:~% cat rtest
    OPS = {
      '=' => proc { |a, b| return a == b ? 1 : 0 },
      '==' => proc { |a, b| send(:equals, a, b) },
    }

    def equals(a, b)
      return a == b ? 1 : 0
    end

    puts OPS['='].call(1, 1)
    puts OPS['=='].call(1, 2)
    lizzy:~% ruby rtest
    1
    0
    lizzy:~% 

But the `==' case is rather ugly. Is there a shorter way than saying `proc {
|a, b| send(:equals, a, b) }'? I.e. is there a way to avoid using the proc
wrapper?

I guess one the problems is that unlike in Python, parentheses are optional
Ruby.  This means that `equals' returns what I am looking for in Python but in
Ruby it causes `equals' to be called. (In Python one has to use `equals()' to
actually perform the call).

Ideas, anybody?

Thanks,
-- 
Jos Backus
jos at catnook.com