exercism/elixir/bread-and-potions

Bread And Potions

Welcome to Bread And Potions on Exercism's Elixir Track. If you need help running the tests or submitting your code, check out HELP.md. If you get stuck on the exercise, check out HINTS.md, but try and solve it without using those first :)

Introduction

Protocols

Protocols are a mechanism to achieve polymorphism in Elixir when you want behavior to vary depending on the data type.

Protocols are defined using defprotocol and contain one or more function headers.

defprotocol Reversible do
  def reverse(term)
end

Protocols can be implemented using defimpl.

defimpl Reversible, for: List do
  def reverse(term) do
    Enum.reverse(term)
  end
end

A protocol can be implemented for any existing Elixir data type or for a struct.

When a protocol function is invoked, the appropriate implementation gets automatically chosen based on the type of the first argument.

Instructions

You're developing your own role-playing video game. In your game, there are characters and items. One of the many actions that you can do with an item is to make a character eat it.

Not all items are edible, and not all edible items have the same effects on the character. Some items, when eaten, turn into a different item (e.g. if you eat an apple, you are left with an apple core).

To allow for all that flexibility, you decided to create an Edible protocol that some of the items can implement.

1. Define edibility

Create the RPG.Edible protocol. The protocol has one function - eat. The eat function accepts an item and a character and returns a by-product and a character.

2. Make loaves of bread edible

Implement the RPG.Edible protocol for the RPG.LoafOfBread item. When eaten, a loaf of bread gives the character 5 health points and has no by-product.

RPG.Edible.eat(%RPG.LoafOfBread{}, %RPG.Character{health: 31})
# => {nil, %RPG.Character{health: 36, mana: 0}}

3. Make mana potions edible

Implement the RPG.Edible protocol for the RPG.ManaPotion item. When eaten, a mana potion gives the character as many mana points as the potion's strength, and produces an empty bottle.

RPG.Edible.eat(%RPG.ManaPotion{strength: 13}, %RPG.Character{mana: 50})
# => {%RPG.EmptyBottle{}, %RPG.Character{health: 100, mana: 63}}

4. Make poisons edible

Implement the RPG.Edible protocol for the RPG.Poison item. When eaten, a poison takes away all the health points from the character, and produces an empty bottle.

RPG.Edible.eat(%RPG.Poison{}, %RPG.Character{health: 3000})
# => {%RPG.EmptyBottle{}, %RPG.Character{health: 0, mana: 0}}

Source

Created by

• @angelikatyborska

Contributed to by

• @neenjaw