public/subjects/traits/README.md

traits

Instructions

Imagine you are designing a new video game, and your next feature is to create food that the players can eat to gain strength.

There are two types of food for now:

• Fruit: increases the strength by 4 units for each kilogram of fruit consumed.
• Meat: has a weight in kilograms, and it's pure fat content as a percentage. The remaining weight of meat which is not pure fat is considered to be protein. Each kilogram of protein increases the strength by 4 units. Each kilogram of fat increases the strength by 9 units.

Define the Food trait for Fruit and Meat. The required method gives returns the amount of strength that the food provides.

Implement the std::fmt::Display trait for the Player structure, so that when {} corresponds to a Player insider a println! macro, it will print 3 lines:

• First: the name of the player.
• Second: strength, score and the money.
• Third: The player's list of weapons.

Expected Functions and Structures

#[derive(Debug)]
pub struct Player {
	pub name: String,
	pub strength: f64,
	pub score: i32,
	pub money: i32,
	pub weapons: Vec<String>,
}

pub struct Fruit {
	pub weight_in_kg: f64,
}

pub struct Meat {
	pub weight_in_kg: f64,
	pub fat_content: f64,
}

impl Player {
	fn eat(&mut self, food: T) {
		self.strength += food.gives();
	}
}

pub trait Food {
	fn gives(&self) -> f64;
}

impl Food for Fruit {
}

impl Food for Meat {
}

Usage

Here is a program to test your functions and traits.

use traits::*;


fn main() {
	let apple = Fruit { weight_in_kg: 1.0 };

	println!("this apple gives {} units of strength", apple.gives());

	let steak = Meat {
		weight_in_kg: 1.0,
		fat_content: 1.0,
	};

	let mut player1 = Player {
		name: String::from("player1"),
		strength: 1.0,
		score: 0,
		money: 0,
		weapons: vec![String::from("knife")],
	};
	println!("Before eating {:?}", player1);
	player1.eat(apple);
	println!("After eating an apple\n{}", player1);
	player1.eat(steak);
	println!("After eating a steak\n{}", player1);
}

And its output:

$ cargo run
this apple gives 4 units of strength
Before eating Player { name: "player1", strength: 1.0, score: 0, money: 0, weapons: ["knife"] }
After eating an apple
player1
Strength: 5, Score: 0, Money: 0
Weapons: ["knife"]
After eating a steak
player1
Strength: 14, Score: 0, Money: 0
Weapons: ["knife"]
$

Notions

• Traits