Closures

In Capturing References or Moving Ownership

It mentions:

Closures can capture values from their environment in three ways, which directly map to the three ways a function can take a parameter:

• borrowing immutably,
• borrowing mutably, and
• taking ownership.

The following example demonstrates these the first two ways:

fn main() {
    // 1. Define a mutable list
    let mut list = vec![1, 2, 3];
    println!("Before defining closure: {list:?}");

    // 2. Define a closure that only borrows the list
    let only_borrows = || println!("From closure: {list:?}");

    println!("Before calling closure: {list:?}");
    only_borrows();
    println!("After calling only_borrows closure: {list:?}");

    // 3. Define a closure that borrows mutably
    let mut borrows_mutably = || list.push(7);
    borrows_mutably();
    println!("After calling borrows_mutably closure: {list:?}");

    // 4. The closure _BORROWS_ the list, either mutably or immutably. It DOES NOT TAKE OWNERSHIP of the list.
}

The output of the program is:

Before defining closure: [1, 2, 3]
Before calling closure: [1, 2, 3]
From closure: [1, 2, 3]
After calling only_borrows closure: [1, 2, 3]
After calling borrows_mutably closure: [1, 2, 3, 7]

Chapter 1

    graph TD;
        E-->F;
        E-->G;
        F-->H;
        G-->H;

Chapter 1

Chapter 3

    graph TD;
        E-->F;
        E-->G;
        F-->H;
        G-->H;

chapter 3