Indexing a String

Question

I want to perform a very simple task, but I cannot manage to stop the compiler from complaining.

fn transform(s: String) -> String {
    let bytes = s.as_bytes();
    format!("{}/{}", bytes[0..2], bytes[2..4])
}

[u8] does not have a constant size known at compile-time.

Some tips making this operation to work as intended?

A.B. · Accepted Answer · 2015-06-23 07:34:21Z

5

Indeed, the size of a [u8] isn't known at compile time. The size of &[u8] however is known at compile time because it's just a pointer plus a usize representing the length of sequence.

format!("{:?}/{:?}", &bytes[0..2], &bytes[2..4])

Rust strings are encoded in utf-8, so working with strings in this way is generally a bad idea because a single unicode character may consist of multiple bytes.

edited Jun 23, 2015 at 7:34

answered Jun 23, 2015 at 7:29

A.B.

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2 Comments

anthony de meulemeester Over a year ago

damn thx. Comming from high level languages doenst make me smart i guess.

aochagavia Over a year ago

feel free to mention anything you would like to have clarified :)

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