Procs can't accept blocks as implicit arguments (the format you're trying). A proc can receive other proc objects as arguments, either explicitly, or using & arguments. Example: a = Proc.new do |&block| block.call end a.call() {puts "hi"}

The important thing to understand is that there is no such thing as a class method in Ruby. A class method is really just a singleton method. There is nothing special about class methods. Every object can have singleton methods. We just call them "class methods" when the object is a Class because "singleton method of an instance of Class" is too long and unwieldy.

Class methods are actually instance methods defined on the singleton class of a class.

It seems inelegant to me to split this into two different modules, one to include, the other to extend.

Apparently when you create a subclass, that subclass's singleton class has # its superclass's singleton class as an ancestor.

I wish to define methods within the class they belong to. Using class << self demonstrates that approach clearly — we are defining methods within the actual singleton class scope.

Class Methods Are Singleton MethodsSince in Ruby classes are objects as well, class methods are merely methods defined on a specific instance of Class.