Implementing Default Values with Traits in Rust

In Rust, managing default values for structs is a common task. Often, you want to create instances of a struct with predefined, sensible values without explicitly setting each field every time. This challenge focuses on using Rust's Default trait to achieve this, allowing for concise and idiomatic initialization of structs.

Problem Description

Your task is to implement the Default trait for a given User struct. This trait provides a default() associated function that returns an instance of the type with default values. You should define sensible default values for each field of the User struct, making it easy to create a new user with common initial settings.

Key Requirements:

• Define a User struct with the following fields:
  • username: a String
  • email: an Option<String> (representing an optional email address)
  • is_active: a bool
  • login_count: a u32
• Implement the std::default::Default trait for the User struct.
• The default() function should return a User instance with the following default values:
  • username: "guest"
  • email: None
  • is_active: false
  • login_count: 0

Expected Behavior:

When User::default() is called, it should return a User struct initialized with the specified default values.

Examples

Example 1:

struct User {
    username: String,
    email: Option<String>,
    is_active: bool,
    login_count: u32,
}

// Implement Default trait here...

fn main() {
    let default_user = User::default();
    println!("Username: {}", default_user.username);
    println!("Email: {:?}", default_user.email);
    println!("Is Active: {}", default_user.is_active);
    println!("Login Count: {}", default_user.login_count);
}

Output:
Username: guest
Email: None
Is Active: false
Login Count: 0

Explanation: Calling User::default() creates an instance of User with all fields set to their predefined default values.

Example 2:

struct User {
    username: String,
    email: Option<String>,
    is_active: bool,
    login_count: u32,
}

// Implement Default trait here...

fn main() {
    let user1 = User::default();
    let user2 = User {
        username: "admin".to_string(),
        ..User::default() // Use default for remaining fields
    };

    println!("User 1 Active: {}", user1.is_active);
    println!("User 2 Active: {}", user2.is_active);
}

Output:
User 1 Active: false
User 2 Active: false

Explanation: This example demonstrates how User::default() can be used to provide default values for fields not explicitly set during struct initialization, showcasing the utility of the Default trait.

Constraints

• The User struct must be defined as described.
• The std::default::Default trait must be implemented for User.
• The default() function must adhere to the specified default values.
• The solution should be written entirely in Rust.

Notes

• Remember that String and Option<String> also implement Default. String::default() returns an empty string, and Option::<T>::default() returns None. You can leverage these existing Default implementations.
• Consider how you would initialize a User struct if you didn't have the Default trait implemented to appreciate its usefulness.
• The .. syntax in struct initialization can be used to fill in remaining fields with their default values if the type implements Default.