From: Clifford Heath <no.spam@...>
Date: 2007-01-31T14:35:07+09:00
Subject: Tricks with method as superclass

I'm intrigued by the way Camping uses a method invocation to
serve as a superclass, and while exploring, possibly found a
bug? At any rate, some behaviour I can't explain... but first
a simple example of what Camping does:

class Foo
    def initialize(*args)
        puts "Initializing Foo"
    end
end
				=> nil

def Foo(*args)
    puts args.inspect
    Class.new(Foo) # Interesting that this works...
end
				=> nil

class Bar < Foo("Hi there!")
end
				["Hi there!"]
				=> nil

Bar.new
				Initializing Foo
				=> #<Bar:0x2f84358>

Ok, all's well, and it's basically what Camping does.
Now what if I want to pass a *block* to the method
that will return my superclass?

def Foo(*args, &block)
    puts args.inspect
    block.call if block
    Class.new(Foo)
end
				=> nil

class Bar < Foo("Hi There!") {
	puts "Surprise!"
    }
end
				["Hi there!"]
				Surprise!
				=> nil

Cool, that worked well. Now I want to keep the args and block passed
that was passed to the method, so I tried the following, which makes
an anonymous subclass of Foo, and Bar is a subclass of that:

class Foo
    def initialize(*args)
        puts "Initializing Foo"
    end
end
				=> nil

def Foo(*args, &block)
    puts args.inspect
    block.call if block
    Class.new(Foo).instance_eval <<-END
            def initialize
		# I'm going to do something with block and args here
                puts "Double surprise!"
            end
            self
        END
end
				=> nil

class Bar < Foo("Hi there!") {
        puts "Surprise!"
    }
end
				["Hi there!"]
				Surprise!
				=> nil

Bar.new
				Initializing Foo
				=> #<Bar:0x2f776b0>

What happened to my Double surprise? It seems that instance_eval hasn't
caused Bar.new to use my extra layer of initialize... The instance of
Bar has the anonymous superclass in it's hierarchy, but the initialize()
doesn't appear in the call stack. What gives here?

Clifford Heath.