Borrowing with Functions

As part of borrow checking, the compiler needs to reason about how borrows flow into and out of functions. In the simplest case borrows last for the duration of the function call:

# // Copyright 2025 Google LLC
# // SPDX-License-Identifier: Apache-2.0
#
fn borrows(x: &i32) {
    dbg!(x);
}

fn main() {
    let mut val = 123;

    // Borrow `val` for the function call.
    borrows(&val);

    // Borrow has ended and we're free to mutate.
    val += 5;
}

• In this example we borrow val for the call to borrows. This would limit our ability to mutate val, but once the function call returns the borrow has ended and we're free to mutate again.