Working with Protocols and Behaviours Elixir
Welcome to this comprehensive, student-friendly guide on working with protocols and behaviours in Elixir! 🎉 If you’re new to these concepts, don’t worry. We’re going to break everything down step-by-step, so by the end of this tutorial, you’ll have a solid understanding and be ready to apply these concepts in your own projects.
What You’ll Learn 📚
- Understanding what protocols and behaviours are in Elixir
- How to implement and use protocols
- How to define and use behaviours
- Common pitfalls and how to avoid them
Introduction to Protocols and Behaviours
In Elixir, protocols and behaviours are powerful tools that help you write flexible and maintainable code. They allow you to define a set of functions that different data types can implement, enabling polymorphism. This might sound a bit abstract right now, but hang in there! We’ll make it clear with examples. 😊
Key Terminology
- Protocol: A way to define a set of functions that can be implemented by different data types.
- Behaviour: A way to define a set of functions that a module must implement, similar to interfaces in other languages.
Getting Started with Protocols
The Simplest Example
defprotocol Size do
@doc "Returns the size of a data structure."
def size(data)
end
defimpl Size, for: List do
def size(list), do: length(list)
end
IO.puts Size.size([1, 2, 3]) # Output: 3Here, we define a protocol Size with a function size/1. We then implement this protocol for lists, using the built-in length/1 function to return the size of the list.
Progressively Complex Examples
Example 1: Protocols with Multiple Implementations
defimpl Size, for: Map do
def size(map), do: map_size(map)
end
IO.puts Size.size(%{a: 1, b: 2}) # Output: 2In this example, we implement the Size protocol for maps. We use map_size/1 to get the number of key-value pairs in the map.
Example 2: Using Protocols with Custom Types
defmodule Circle do
defstruct radius: 0
end
defimpl Size, for: Circle do
def size(%Circle{radius: r}), do: 3.14 * r * r
end
IO.puts Size.size(%Circle{radius: 5}) # Output: 78.5Here, we define a custom struct Circle and implement the Size protocol to calculate the area of the circle.
Understanding Behaviours
Defining a Behaviour
defmodule LoggerBehaviour do
@callback log(String.t()) :: :ok
endBehaviours in Elixir are defined using the @callback directive. Here, we define a behaviour LoggerBehaviour with a single function log/1 that takes a string and returns :ok.
Implementing a Behaviour
defmodule ConsoleLogger do
@behaviour LoggerBehaviour
def log(message) do
IO.puts("Log: #{message}")
:ok
end
end
ConsoleLogger.log("Hello, World!") # Output: Log: Hello, World!In this example, we implement the LoggerBehaviour in a module ConsoleLogger. We define the log/1 function to print the message to the console.
Common Questions and Answers
- What is the difference between protocols and behaviours?
Protocols are used for polymorphism, allowing different data types to implement the same set of functions. Behaviours are more like interfaces, ensuring that a module implements certain functions.
- Can a module implement multiple protocols?
Yes, a module can implement multiple protocols, allowing it to behave differently based on the protocol being used.
- How do I troubleshoot a ‘protocol not implemented’ error?
Ensure that you’ve implemented the protocol for the specific data type you’re working with. Check for typos in the protocol or implementation.
- Why use behaviours instead of just defining functions?
Behaviours enforce a contract, ensuring that all modules implementing the behaviour have the required functions. This is useful for consistency and reliability in larger applications.
Troubleshooting Common Issues
If you encounter a ‘protocol not implemented’ error, double-check that the data type you’re using has an implementation for the protocol. Also, ensure that the function signatures match exactly.
Remember, protocols are about polymorphism, while behaviours are about enforcing a contract. Use them accordingly to keep your code clean and maintainable!
Practice Exercises
- Implement a protocol for calculating the perimeter of different shapes.
- Create a behaviour for a notification system with different implementations for email and SMS notifications.
For more information, check out the Elixir Protocols Documentation and Elixir Behaviours Documentation.