feat: traits exercises

exercises/traits/README.md

@@ -0,0 +1,11 @@
+# Traits
+
+A trait is a collection of methods.
+
+Data types can implement traits. To do so, the methods making up the trait are defined for the data type. For example, the `u256` data type implements the `Into` trait. This allows a user to write `1.into()` to convert a felt into a u256.
+
+In this way, traits are somewhat similar to Java interfaces and C++ abstract classes.
+
+Because traits indicate shared behavior between data types, they are useful when writing generics.
+
+- [Traits & Impls](https://link.medium.com/IQGqboBerxb#83b5)

exercises/traits/traits1.cairo

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+// traits1.cairo
+// Time to implement some traits!
+
+// Your task is to implement the trait
+// `AnimalTrait` for the type `Animal`
+//
+// Execute `starklings hint traits1` or use the `hint` watch subcommand for a hint.
+
+// Fill in the impl block to make the code work.
+
+#[derive(Copy, Drop)]
+struct Animal {
+ noise: felt
+}
+
+trait AnimalTrait<T> {
+ fn new(noise: felt) -> T;
+ fn make_noise(self: T) -> felt;
+}
+
+impl AnimalImpl of AnimalTrait::<Animal> {
+ // TODO: implement the trait AnimalTrait for Animal
+}
+
+#[test]
+fn test_traits1() {
+ // TODO make the test pass by creating two instances of Animal
+ // and calling make_noise on them
+ let cat: Animal = AnimalTrait::new('meow');
+ assert(cat.make_noise() == 'meow', 'Wrong noise');
+
+ assert(cow.make_noise() == 'moo', 'Wrong noise');
+}

exercises/traits/traits2.cairo

@@ -0,0 +1,44 @@
+// traits2.cairo
+
+// The previous exercise did not make the distinction
+// between different types of animals, but this one does.
+// The trait `AnimalTrait` has two functions:
+// `new` and `make_noise`.
+// `new` should return a new instance of the type
+// implementing the trait.
+// `make_noise` should return the noise the animal makes.
+// The types `Cat` and `Cow` are already defined for you.
+// You need to implement the trait `AnimalTrait` for them.
+
+// No hints for this one!
+// Execute `starklings hint traits2` or use the `hint` watch subcommand for a hint.
+
+#[derive(Copy, Drop)]
+struct Cat {
+ noise: felt, 
+}
+
+#[derive(Copy, Drop)]
+struct Cow {
+ noise: felt, 
+}
+
+trait AnimalTrait<T> {
+ fn new() -> T;
+ fn make_noise(self: T) -> felt;
+}
+
+impl CatImpl of AnimalTrait::<Cat> {
+ // TODO: implement the trait Animal for the type Cat
+}
+
+// TODO: implement the trait Animal for the type Cow
+
+#[test]
+fn test_traits2() {
+ let kitty: Cat = AnimalTrait::new();
+ assert(kitty.make_noise() == 'meow', 'Wrong noise');
+
+ let cow: Cow = AnimalTrait::new();
+ assert(cow.make_noise() == 'moo', 'Wrong noise');
+}

exercises/traits/traits3.cairo

@@ -0,0 +1,76 @@
+// traits3.cairo
+//
+// The previous exercise showed how to implement a trait for multiple types.
+// This exercise shows how you can implement multiple traits for a single type.
+// This is useful when you have types that share some common functionality, but
+// also have some unique functionality.
+
+// Execute `starklings hint traits3` or use the `hint` watch subcommand for a hint.
+
+#[derive(Copy, Drop)]
+struct Fish {
+ noise: felt,
+ distance: u32,
+}
+
+#[derive(Copy, Drop)]
+struct Dog {
+ noise: felt,
+ distance: u32,
+}
+
+trait AnimalTrait<T> {
+ fn new() -> T;
+ fn make_noise(self: T) -> felt;
+ fn get_distance(self: T) -> u32;
+}
+
+trait FishTrait {
+ fn swim(ref self: Fish) -> ();
+}
+
+trait DogTrait {
+ fn walk(ref self: Dog) -> ();
+}
+
+impl AnimalFishImpl of AnimalTrait::<Fish> {
+ fn new() -> Fish {
+ Fish { noise: 'blub', distance: 0_u32 }
+ }
+ fn make_noise(self: Fish) -> felt {
+ self.noise
+ }
+ fn get_distance(self: Fish) -> u32 {
+ self.distance
+ }
+}
+
+impl AnimalDogImpl of AnimalTrait::<Dog> {
+ fn new() -> Dog {
+ Dog { noise: 'woof', distance: 0_u32 }
+ }
+ fn make_noise(self: Dog) -> felt {
+ self.noise
+ }
+ fn get_distance(self: Dog) -> u32 {
+ self.distance
+ }
+}
+
+// TODO: implement FishTrait for the type Fish
+
+// TODO: implement DogTrait for the type Dog
+
+#[test]
+fn test_traits3() {
+ // Don't modify this test!
+ let mut salmon: Fish = AnimalTrait::new();
+ salmon.swim();
+ assert(salmon.make_noise() == 'blub', 'Wrong noise');
+ assert(salmon.get_distance() == 1_u32, 'Wrong distance');
+
+ let mut dog: Dog = AnimalTrait::new();
+ dog.walk();
+ assert(dog.make_noise() == 'woof', 'Wrong noise');
+ assert(dog.get_distance() == 1_u32, 'Wrong distance');
+}

info.toml

@@ -286,4 +286,40 @@ For get_fees: This method takes an additional argument, is there a field in the
 
 Looking at the test functions will also help you understand more about the syntax.
 This section will help you understanding more about impls and traits: https://link.medium.com/c8TqX7R3qxb#83b5.
-"""
+"""
+
+
+# TRAITS
+
+[[exercises]]
+name = "traits1"
+path = "exercises/traits/traits1.cairo"
+mode = "test"
+hint = """ 
+If you want to implement a trait for a type, you have to implement all the methods in the trait.
+Based on the signature of the method, you can easily implement it.
+
+In the test, you need to instantiate two objects of type `Animal`.
+You can call the method of a trait by using the MyTrait::foo() syntax.
+How would you instantiate the two objects with AnimalTrait?
+Maybe you need to specify the type of the object?
+"""
+
+[[exercises]]
+name = "traits2"
+path = "exercises/traits/traits2.cairo"
+mode = "test"
+hint = """ No hints for this one! It is very similar to the previous exercise."""
+
+[[exercises]]
+name = "traits3"
+path = "exercises/traits/traits3.cairo"
+mode = "test"
+hint = """ 
+You can implement multiple traits for a type.
+When a trait is destined to be implemented by a single type, you don't need to use generics.
+If you're having trouble updating the distance value in the `Fish` and `Dog` impls, remember that you need to first
+1. Destructure the object into mutable variables
+2. Update the distance variable
+3. Reconstruct `self` with the updated variables (`self = MyStruct { ... }`) 
+"""