Behaviors in Elixir (and Erlang) are a way to separate and abstract the generic part of a component (which becomes the behavior module) from the specific part (which becomes the callback module). Behaviors provide a way to −

• Define a set of functions that have to be implemented by a module.
• Ensure that a module implements all the functions in that set.

If you have to, you can think of behaviors like interfaces in object oriented languages like Java: a set of function signatures that a module has to implement.

Defining a Behaviour

Let us consider an example to create our own behavior and then use this generic behavior to create a module. We will define a behavior that greets people hello and goodbye in different languages.

defmodule GreetBehaviour do
   @callback say_hello(name :: string) :: nil
   @callback say_bye(name :: string) :: nil
end

The @callback directive is used to list the functions that adopting modules will need to define. It also specifies the no. of arguments, their type and their return values.

Adopting a Behaviour

We have successfully defined a behavior. Now we will adopt and implement it in multiple modules. Let us create two modules implementing this behavior in English and Spanish.

defmodule GreetBehaviour do
   @callback say_hello(name :: string) :: nil
   @callback say_bye(name :: string) :: nil
end

defmodule EnglishGreet do
   @behaviour GreetBehaviour
   def say_hello(name), do: IO.puts("Hello "  name)
   def say_bye(name), do: IO.puts("Goodbye, "  name)
end

defmodule SpanishGreet do
   @behaviour GreetBehaviour
   def say_hello(name), do: IO.puts("Hola "  name)
   def say_bye(name), do: IO.puts("Adios "  name)
end

EnglishGreet.say_hello("Ayush")
EnglishGreet.say_bye("Ayush")
SpanishGreet.say_hello("Ayush")
SpanishGreet.say_bye("Ayush")

Hello Ayush
Goodbye, Ayush
Hola Ayush
Adios Ayush