Variables

Binding and mutability

🌟 A variable can be used only if it has been initialized.


// Fix the error below with least amount of modification to the code
fn main() {
    let x: i32; // Uninitialized but used, ERROR !
    let y: i32; // Uninitialized but also unused, only a Warning !

    assert_eq!(x, 5);
    println!("Success!");
}

🌟 Use mut to mark a variable as mutable.


// Fill the blanks in the code to make it compile
fn main() {
    let __ __ = 1;
    __ += 2; 
    
    assert_eq!(x, 3);
    println!("Success!");
}

Scope

A scope is the range within the program for which the item is valid.

🌟


// Fix the error below with least amount of modification
fn main() {
    let x: i32 = 10;
    {
        let y: i32 = 5;
        println!("The value of x is {} and value of y is {}", x, y);
    }
    println!("The value of x is {} and value of y is {}", x, y); 
}

🌟🌟


// Fix the error with the use of define_x
fn main() {
    println!("{}, world", x); 
}

fn define_x() {
    let x = "hello";
}

Shadowing

You can declare a new variable with the same name as a previous variable, here we can say the first one is shadowed by the second one.

🌟🌟


// Only modify `assert_eq!` to make the `println!` work(print `42` in terminal)
fn main() {
    let x: i32 = 5;
    {
        let x = 12;
        assert_eq!(x, 5);
    }

    assert_eq!(x, 12);

    let x = 42;
    println!("{}", x); // Prints "42".
}

🌟🌟


// Remove a line in the code to make it compile
fn main() {
    let mut x: i32 = 1;
    x = 7;
    // Shadowing and re-binding
    let x = x; 
    x += 3;


    let y = 4;
    // Shadowing
    let y = "I can also be bound to text!"; 

    println!("Success!");
}

Unused variables

Fix the warning below with :

🌟 Only one solution
🌟🌟 Two distinct solutions

Note: none of the solutions is to remove the line let x = 1


fn main() {
    let x = 1; 
}

// Warning: unused variable: `x`

Destructuring

🌟🌟 We can use a pattern with let to destructure a tuple to separate variables.

Tips: you can use Shadowing or Mutability


// Fix the error below with least amount of modification
fn main() {
    let (x, y) = (1, 2);
    x += 2;

    assert_eq!(x, 3);
    assert_eq!(y, 2);

    println!("Success!");
}

Destructuring assignments

Introduced in Rust 1.59: You can now use tuple, slice, and struct patterns as the left-hand side of an assignment.

🌟🌟

Note: the feature Destructuring assignments need 1.59 or higher Rust version


fn main() {
    let (x, y);
    (x,..) = (3, 4);
    [.., y] = [1, 2];
    // Fill the blank to make the code work
    assert_eq!([x,y], __);

    println!("Success!");
}

You can find the solutions here(under the solutions path), but only use it when you need it

Rust By Practice