82 lines
2.7 KiB
Markdown
82 lines
2.7 KiB
Markdown
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# Bread And Potions
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Welcome to Bread And Potions on Exercism's Elixir Track.
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If you need help running the tests or submitting your code, check out `HELP.md`.
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If you get stuck on the exercise, check out `HINTS.md`, but try and solve it without using those first :)
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## Introduction
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## Protocols
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Protocols are a mechanism to achieve polymorphism in Elixir when you want behavior to vary depending on the data type.
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Protocols are defined using `defprotocol` and contain one or more function headers.
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```elixir
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defprotocol Reversible do
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def reverse(term)
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end
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```
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Protocols can be implemented using `defimpl`.
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```elixir
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defimpl Reversible, for: List do
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def reverse(term) do
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Enum.reverse(term)
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end
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end
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```
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A protocol can be implemented for any existing Elixir data type or for a struct.
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When a protocol function is invoked, the appropriate implementation gets automatically chosen based on the type of the first argument.
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## Instructions
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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.
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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).
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To allow for all that flexibility, you decided to create an `Edible` protocol that some of the items can implement.
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## 1. Define edibility
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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.
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## 2. Make loaves of bread edible
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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.
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```elixir
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RPG.Edible.eat(%RPG.LoafOfBread{}, %RPG.Character{health: 31})
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# => {nil, %RPG.Character{health: 36, mana: 0}}
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```
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## 3. Make mana potions edible
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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.
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```elixir
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RPG.Edible.eat(%RPG.ManaPotion{strength: 13}, %RPG.Character{mana: 50})
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# => {%RPG.EmptyBottle{}, %RPG.Character{health: 100, mana: 63}}
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```
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## 4. Make poisons edible
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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.
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```elixir
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RPG.Edible.eat(%RPG.Poison{}, %RPG.Character{health: 3000})
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# => {%RPG.EmptyBottle{}, %RPG.Character{health: 0, mana: 0}}
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```
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## Source
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### Created by
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- @angelikatyborska
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### Contributed to by
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- @neenjaw
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