Comment by haberman | Hacker News Reader

Comment by haberman | Hacker News Reader

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> (Have to double space due to lack of formatting capabilities here.)

Indent by four spaces to get a <pre> tag:

    let mut v = vec![1i32, 2, 3, 4, 5];
    let vlen = v.len()
    for i in range(0, vlen) {
        let x = &mut v[i];

        // do some work with x
    }

> This seems to be a forgotten technology.

Given what I know about Rust, I strongly suspect that there is a way in Rust to iterate over a vector with only a single hoisted bounds-check. Hopefully other Rust people can chime in on what this is.

In most cases, you use iterators rather than indexing

    for x in v.iter_mut() {
        // do some work with x
    }

or if you need the index

    for (i, x) in v.iter_mut().enumerate() {
        // do some work with x and i
    }

similar to Python's enumerate(). These loops never need to do any bounds-checking, even when compiling without optimization.

In this example the iteration count is a small compile-time constant (5), and the loop body is small, so when compiling with optimizations the loop will be unrolled.

> I strongly suspect that there is a way in Rust to iterate over a vector with only a single hoisted bounds-check. Hopefully other Rust people can chime in on what this is.

Iterators.

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