From: Eric Mahurin <eric.mahurin@...>
Date: 2006-09-18T02:38:17+09:00
Subject: redefining/overriding methods in builtin classes AND their subclasses

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I just found out that ruby seems to treat subclasses of builtin classes
about the same as the builtin classes themselves.  For the sake of
performance, ruby many times bypasses normal method call mechanisms for many
builtin classes (and their subclasses) and effectively inlines the original
definition.  This is kind of frustrating that ruby does this even for
subclasses of builtin classes.  Object, Class, Module shouldn't be a problem
since they are meant to be subclassed (with some exceptions like
Object#__send__), but String, Array, immediate classes and probably others
could be a problem.  Of course you can't even subclass the immediate classes
anyways.

Here is an example showing the issue when I tried to override the definition
of #to_s in a subclass of String:

class SubclassedString < String
    def to_s
        "subclassed:#{super}"
    end
end

puts SubclassedString.new("hello")

class String
    def to_s
        "redefined:" + self.to_str
    end
end

puts String.new("hello")

require 'delegate'

class DelegatedString < DelegateClass(String)
    def initialize(*args)
        super(String.new(*args))
    end
    def to_s
        "delegated:#{super}"
    end
end

puts DelegatedString.new("hello")


Only the DelegatedString does what is expected.  Redefining/overriding #to_s
in String or a subclass of it is pretty much ignored (since the original
definition was inlined in the C code).

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