Why someone prefer to define class method as `module SomeModule extend self` but not `class SomeClass ; def self.method`?

I am writing Ruby code.

The code before refactoring looks like:

class Tool
   def self.say_hi
     return "hi"
   end 
end

and after refactored by my workmates:

module Tool
   extend self 
   def say_hi
     return "hi"
   end
end

both style of code can work as: Tool.say_hi.

I want to know what's the pros and cons for his style. thanks.

They have changed the class for a module, the main difference is that modules can be included in other class to reuse that say_hi method.

class Toolbox
  include Tool
end

Toolbox.new.say_hi

But I don't know if that was the main driver for the refactor, another difference between the two approaches is that you can control the visibility of the method with the second snippet.

module Tool
  extend self

  private
  def say_hi
    return "hi"
  end
end

Tool.say_hi

Will return private method 'say_hi' called for Tool:Module (NoMethodError meanwhile this would just work.

class Tool

  private
  def self.say_hi
    return "hi"
  end
end
Tool.say_hi