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Closures in Rust are categorized based on how they interact with the environment and the variables they capture. The three main types are Fn, FnMut, and FnOnce. Understanding and using these types effectively is key to mastering closures in Rust.

Closure Type Definitions

  • Fn: A closure that borrows its environment immutably. It is useful for read-only operations.
  • FnMut: A closure that mutably borrows its environment, allowing it to modify variables.
  • FnOnce: A closure that takes ownership of its captured variables, consuming them in the process.

Your Task

Implement the following closures and their respective behaviors:

  • calculate_total: An Fn closure that calculates the total price of an item, including tax (price + price * tax_rate).
  • apply_discount: An FnMut closure that mutates the cart total by subtracting a given discount.
  • checkout_cart: An FnOnce closure that consumes the cart's details (a String) and returns a confirmation message.

Hints

<details> <summary>Click here to reveal hints</summary>
  • Use impl Fn, impl FnMut, or impl FnOnce to define the types of the closures. e.g. 
      pub fn return_closure() -> impl Fn(f64, f64) -> f64 {
          //
      }
</details>
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// 1. Based on the `main` function below,
// Find out the types of the closures and define them
pub fn create_typed_closures() {
    // 2. Implement calculate_total closure here
    let calculate_total = || {};


    // 3. Implement apply_discount closure here
    let apply_discount = || {};


    // 4. Implement checkout_cart closure here
    let checkout_cart = || {};


    (calculate_total, apply_discount, checkout_cart)
}


// Example usage
pub fn main() {
    let (calculate_total, mut apply_discount, checkout_cart) = create_typed_closures();


    // Example tests
    assert_eq!(calculate_total(100.0, 0.2), 120.0);


    let mut total_price = 120.0;
    apply_discount(&mut total_price, 20.0);
    assert_eq!(total_price, 100.0);


    let cart_details = String::from("Items: Apple, Banana, Orange");
    assert_eq!(
        checkout_cart(cart_details),
        "Checkout complete: Items: Apple, Banana, Orange"
    );
}