Intro to Reading Ruby Doc: What's M, C, ::, # ?

Xah Lee, 2013-01-01

This page is a guide to reading Ruby's official doc, for Ruby beginners.

Ruby Doc home page is at http://ruby-doc.org/

On top, you can see {Core, Std-lib, Gems}. These are most important.

• Core = Ruby language core stuff.
• Std-lib = Ruby standard library stuff.
• Gems = Third-party libraries.

For beginner, you'd be concerned with the Core and Std-lib.

Now, look at the Ruby Core doc page: http://ruby-doc.org/core-1.9.3/. The left side are classes. The right side are methods.

On the left side, the classes, some have a gray “C” some have “M”.

• C = Class.
• M = Mixin. (a mixin is similar to Java's abstract class. It's to be inherited by other class, but not meant for instantiation.)

This means, for beginner, you can probably ignore all those M ones.

On the right side, are methods, with :: or #.

• :: → class method. (Class Methods are those you can call without having a object. For example, the “new” in Array.new(10) is a class method.)
• # → instance method. (Instance Methods requires a object. For example, the “first” in [3,4,5].first is a instance method.)