Q:

Is the puts function of ruby a method of an object?

I'm trying to understand how the puts function fits in Ruby's "Everything is an object" stance.
Is puts is the method of a somehow hidden class/object? Or is it a free-floating method, with no underlying object?

A:

I'm trying to understand how the puts function fits in Ruby's "Everything is an object" stance.

First off, puts is not a function. It's sole purpose is to have a side-effect (printing something to the console), whereas functions cannot have side-effects … that's the definition of "function", after all.
Ruby doesn't have functions. It only has methods. Thus, puts is a method.

Is puts is the method of a somehow hidden class/object?

No, it's just a boring old instance method of a boring old class. (Well, a boring old instance method of a boring old mixin, actually, but a mixin is just a class which abstracts over its superclass.)
Kernel is mixed into Object, which is the (default) superclass of all objects (modulo BasicObject, of course), thus, Kernel is a common superclass (or "supermixin", if you prefer) of (almost) all objects in Ruby.

Or is it a free-floating method, with no underlying object?

There is no such thing. A method is always associated with an object (the receiver of the message), that's what makes it a "method". (At least in OO parlance. In ADT-oriented languages, the word "method" means something slightly different.)
By the way, the easiest option is always to just ask Ruby herself:
method(:puts).owner
# => Kernel

