From: "Stephan Kämper" <Stephan.Kaemper@...>
Date: 2004-05-02T20:23:59+09:00
Subject: Commutativity of '*'

Hi all,

say I have a new class Foo which provides * as a multiplicative method.
Now, given the following lines:

def some_operation_using( lft, rgt )
   return "#{lft} times #{rgt}"
end

class Foo

  def *( other )
     # do something
     res = some_operation_using( other, self )
     return res
   end

   def to_s
	return "a Foo thingy."
   end

end

# That given, the following lines will work

f = Foo.new
puts f * 42.0

# But this won't. Instead I get:
# .../lm.rb:25:in `*': Foo can't be coerced into Float (TypeError)
#	from .../lm.rb:25
puts 42.0 * f

What would be a (or even the) Ruby Way to get the last line to work?
Some method to coerce a Foo into a Float? Or some hacking of Float 
itself? Like adding that, for example:

class Float
   alias old_mult *
   def *( other )
     if other.class == Foo
       return other * self
     else
       return self.old_mult( other )
     end
   end
end

That doesn't seem to be terribly elegant, I think.

Any other way?

Happy rubying

Stephan