Table of contents📚

What is a trait❔
- Example
Implementing a trait
Using traits

Implementing traits

What is a trait❔

A trait is a set of methods common to each type. It is similar to an interface in other languages.

Example

The std::fmt::Display trait is a trait that defines how to display a type.

println!("{}", 42);

Here, 42 is a value of type i32, and cannot be printed directly because it is not a string.

It first needs to be formatted into a string.

And that is what the Display trait does.

When we run

println!("{}", 42);

The println! macro will call the Display trait implementation for i32 to format the value into a string and print it.

This is the same for other types, such as f32, Vectors…

Implementing a trait

First, we need a struct to implement the trait on :

struct Person {
    name: String,
    age: u8,
    hobbies: Vec<String>,
    country: String,
    company: String,
}

We will implement the to_string trait for the Person struct.

This method will return a string representation of the instance of the struct.

To implement a trait, we need to use the impl keyword and the following syntax:

impl ToString for Person {
    fn to_string(&self) -> String {
        format!("Hi, my name is {}, I'm {} years old and I live in {}. I work at {} and my hobbies are: {}", self.name, self.age, self.country, self.company , self.hobbies.join(", "))
    }
}

ℹ️ The format! macro is used like println! but it returns a String instead of printing to the console.

Using traits

We can now create a new instance of the struct and use the to_string method:

let person = Person {
    name: String::from("Léopold"),
    age: 13,
    hobbies: vec![String::from("💻"), String::from("🛌"), String::from("🍔")],
    country: String::from("France 🇫🇷"),
    company: String::from("Skwal-net"),
};

let presentation = person.to_string();

println!("{}", presentation);

ℹ️ The traits name are the same for all types.

Output:

Hi, my name is Léopold, I'm 13 years old and I live in France 🇫🇷. I work at Skwal-net and my hobbies are: 💻, 🛌, 🍔

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