Question

I’m a C++ programmer learning Ruby. In a beginner book I read:

“A class is itself an object, even if you don’t directly instantiate it.”

I don’t know how to interpret that.

Answer 1

In C++, with the exception of typeid et al, there’s no language-visible runtime representation of a class. You can say class Foo {};, but then you can’t say &Foo. (You can get the typeid / address of the typeinfo object, which is a bastardized version of a class object).

In Ruby, classes are objects. Anything you can do with an object, you can do with a class since it is an object. For example, in Ruby you can foo.send(...) to any object foo. Since a class is an object, you can just as well as Foo.send(...).

The part about “you didn’t instanciate it” refers to the fact that usually you say foo = Foo.new in Ruby but you don’t need to say that for classes. The class object is created by the runtime. (In fact, class Foo; end in Ruby is pretty similar to Foo = Class.new.)