From: "Jonas Pfenniger (zimbatm)" Date: 2011-01-21T00:58:11+09:00 Subject: Re: Singleton class, metaclass, eigenclass: what do they mean? 2011/1/16 Josh Cheek : > 1. Is this already outdated, now that there is Object#singleton_class ? > After this thread, I had taken to calling them singleton classes, but then I > got to this spot in the book, and now I'm not sure again. It seems that 1.9 has more or less standardized on the singleton_class and singleton_method names, but if you look into ruby's source code, for example in class.c, you'll find an ENSURE_EIGENCLASS define or make_metaclass method. There was a big thread on this same mailing-list discussing the issue. 2011/1/16 Josh Cheek : > 2. Why do people say that singleton class is unrelated to the singleton > design pattern, when the singleton design pattern is a way to define a class > with only one instance, and an objects singleton class has the object as its > only instance? Maybe it's because inheriting classes also inherit of the singleton methods defined on the parent class, but I'm making things up. I don't remember the details. Eigenclass was cool IMO, because it's a weird name, and make ruby special.