A different approach, compared to using `Module#module_function`

versatile_methods.rb

# The idea here is to make all the methods below accessible through the module
# itself and through the classes including the module, but having the methods
# publicly available both as instance and as class methods.
module A
  def self.abc = 123
  def self.xyz = 456

  def self.append_features(klass)
    methods_being_added = singleton_methods - [:append_features]
    delegation_setter = ->(mod, methods) { delegate *methods, to: mod }

    [klass.singleton_class, klass].each do |receiver|
      receiver.class_exec(self, methods_being_added, &delegation_setter)
    end
  end
end

class B
  include A
end

# Methods accessible through the module itself:
[A.abc, A.xyz] # => [123, 456]

# Methods accessible as instance methods in the class that has the module included:
[B.new.abc, B.new.xyz] # => [123, 456]

# And last but not least, the same methods accessible through class methods:
[B.abc, B.xyz] # => [123, 456]