Is a Ruby module equivalent to a Java Interface?

Question

As I understand it, an interface is Java is intended to enforce a design by laying out methods for classes implementing the interface to fill in. Is this the idea with a Ruby module also? I see that just like with Interfaces in Java, you can't instantiate a module in Ruby.

Answer 1

The short answer is no.

Here's the reasoning, a Java/C# interface defines the method signatures an implementing class will provide at minimum.

Additionally:

• With ruby modules there is no such contract because of the duck-typing.
• Modules are just a way to extract out common functionality for easy re-use. The closest relation is C# extension methods, but those aren't an exact match since they exist in a static context.
• Modules can add state to an existing class.
• Modules can have static methods
• Modules can act as namespaces

Example:

module SimpleConversation
  class NamespacedExample
    def poke
      puts "ouch"
    end
  end

  attr_accessor :partner_name
  def converse
    partner_name ||= "Slowpoke"
    speak + "\n#{partner_name}: Yes they are"
  end

  def self.yay
    puts "yay"
  end
end

class Foo
  include SimpleConversation
  attr_accessor :name

  def speak
    name ||= "Speedy"
    "#{name}: tacos are yummy"
  end
end

x = Foo.new
x.name = "Joe"
x.partner_name = "Max"
puts x.speak
puts x.converse

y = SimpleConversation::NamespacedExample.new
y.poke

SimpleConversation.yay