Performance Patterns

Borrow Slice

Read Without Copying

Borrowing a slice lets a helper read part of a collection without cloning the data.

Program

Play the program to choose how many numbers the helper reads from the borrowed slice.

borrow_slice.rs 
fn main() {
    let limit = ;
    let values = [3, 4, 5, 6];
    let total = sum_prefix(&values, limit);
    println!("sum={total}");
}

fn sum_prefix(values: &[i32], limit: usize) -> i32 {
    values[..limit].iter().sum()
}

fn main() {
    let limit = ;
    let values = [3, 4, 5, 6];
    let total = sum_prefix(&values, limit);
    println!("sum={total}");
}

fn sum_prefix(values: &[i32], limit: usize) -> i32 {
    values[..limit].iter().sum()
}

fn main() {
    let limit = ;
    let values = [3, 4, 5, 6];
    let total = sum_prefix(&values, limit);
    println!("sum={total}");
}

fn sum_prefix(values: &[i32], limit: usize) -> i32 {
    values[..limit].iter().sum()
}
slice `&values[..limit]` borrows part of the array instead of allocating another collection.
iterator `iter().sum()` reads borrowed values and computes a result.
boundary The helper accepts any `&[i32]`, so callers can pass arrays, vectors, or slices.