From: George Ogata <g_ogata@...>
Date: 2004-02-09T16:24:58+09:00
Subject: Re: === confusion

Ian Macdonald <ian@caliban.org> writes:

> foo = case bar.class
>       when Foo::Bar
>         'abc'
>       when Foo::Bar::Baz
>         'def'
>       when Foo::Qux
>         'ghi'
>       else
>         'jkl'
>       end
>
> The problem is that most comparisons of bar.class fell through to the
> else clause. A quick debugging session on a particular instance of 'bar'
> revealed that 'bar.class == Foo::Bar' was true, but
> 'bar.class === Foo::Bar' was false. Quite honestly, I don't understand
> why, as I'm not overriding === anywhere. My classes are not derived from
> any standard Ruby classes, either, so they should be inheriting ===
> from Object, if I understand things correctly.
>
> I fixed it by changing the start of the case statement to
> 'case bar.class.to_s' and then comparing to strings instead of object
> identifiers, but I would like to understand what exactly === was doing
> in the original case.

This keeps coming up from time to time.

Module#=== returns true iff the argument is an instance of the module
or one of its descendants (from the Pickaxe).  In your code,
`bar.class' returns an instance of `Class', which is of course not a
descendant of `Foo::Bar', `Foo::Bar::Baz', etc., and so falls through
to the else clause.  I think what you want is to remove the `.class'
in the case expression:

foo = case bar
      ##      ^^^^^^ (removed the `.class')
      when Foo::Bar
        'abc'
      when Foo::Bar::Baz
        'def'
      when Foo::Qux
        'ghi'
      else
        'jkl'
      end

HTH