module_function_vs_private_methods

module_function_vs_private_methods.rb

module MyModule
  module_function
  
  def module_foo
    'module_functions are singleton_methods on a module, which allow explicit receiver'
  end
end

class MyClass
  private
  
  def private_foo
    "private instance methods cannot have an explicit receiver, and are not singleton_methods"
  end
end

# module_functions can have an explicit receiver and they are singleton methods
MyModule.module_foo

# private instance methods can only be called on an instance of that class, without an explicit receiver
instance = MyClass.new
begin
  instance.private_foo
rescue
  "you cannot call a private method with an explicit receiver, that is with the '.'(DOT) syntax"
end

# you can however, do this to call a private method
instance.send(:private_foo)