From: Erwin Abbott <erwin.abbott@...>
Date: 2007-05-27T12:13:14+09:00
Subject: Tricky problem with ===

I have a "BlankState" type of class and it's method_missing forwards
everything to an instance variable.  This way I can treat the object
specially in my own code and all other code doesn't need to know the
difference.  For a contrived example:

class Proxy
  # remove methods inherited by Object, etc
  instance_methods.each do |m|
    undef_method m unless m =~ /^__/
  end

  def initialize name, value
    @name, @value = name, value
  end

  def to_myformat
    "#{@name}: #{@value}"
  end

  def method_missing name, *args, &block
    @value.send name, *args, &block
  end
end

object = "regular string"
x = Proxy.new("UID", object)

x.class # => Array
x.size  # => 5
x.to_myformat # => UID: regular string

While that's a pretty boring example, the idea might come in handy for
something like a graph node, or linked list node (etc). Anyway, the
problem I have is the way this works:

case x
when Array puts "Array"
when Proxy puts "Proxy"
end

This calls Array.===(x) which doesn't call x.class, and it returns
false. If I redefine Array.===(other) to test self == other.class then
it works. I can't think of any way to get this to work since it
doesn't appear there are any methods of x being called that I can
intercept. Does ruby get the class 'internally' instead of calling
x.class? I guess if worse comes to worse I can use if x.is_a? Array;
...; elsif x.is_a? Foo; ...; end. I don't want to go about redefining
every class's === method, that seems to be a mess.

Erwin