From: Jim Weirich <jweirich@...>
Date: 2002-03-10T06:22:35+09:00
Subject: Re: What classes exist

>>>>> "David" == David Corbin <dcorbin@imperitek.com> writes:

    David> At the moment, I'm having problem with #2.  In Java, you
    David> can do Class.forName("Foo") to see get a Class object for
    David> class Foo.  The ruby Class class doesn't seem to have this
    David> capability.  Please help

Class names are constants.  Top level class names are constants in
Object.  You can use const_get to fetch the value.  For example ...

    foo_class = Object.const_get("Foo")

If "Foo" is not a class, you will get a NameError in const_get.

If the class is nested in a module (e.g.  Foo::Bar), you have to do a
little more work.  The following code will return the class object for
any class name (including nested classes), or will return nil if there
is no match.

    def class_for(class_name)
      names = class_name.split("::")
      result = Object
      names.each { |n|
        result = result.const_get(n)
      }
      result
    rescue NameError
      nil
    end

You can also use eval to get a constant value, but passing unvalidated
strings to eval is kinda risky.

-- 
-- Jim Weirich     jweirich@one.net    http://w3.one.net/~jweirich
---------------------------------------------------------------------
"Beware of bugs in the above code; I have only proved it correct, 
not tried it." -- Donald Knuth (in a memo to Peter van Emde Boas)