Ruby中的“ Fixnum”和“ 3”有什么区别？

Question

Fixnum.methods.count #=> 99
3.methods.count      #=> 131

If they have different methods I would guess they are not exactly the same thing.

1. What is the difference exactly?

2. What's going on under the hood in Ruby?

I'm using ruby 2.2.1p85 (2015-02-26 revision 49769) .

Answer 1

As @Aetherus said, Fixnum is an instance of a class, so Fixnum.methods return all of its class methods, whereas 3.methods will return Fixnum instance methods, since 3 is an instance of Fixnum .

For example, basic math operators are instance methods, such as :+ , :- , etc, so Fixnum.respond_to?(:+) returns false . And 3.respond_to?(:class_variables) returns false , because that method is a class method, so instances of that class does not have access to it.