Crate in_place_string_map

in_place_string_map is a library for doing string manipulation in place.

Normally in Rust, if you wanted to handle escapes, for example, you’d need to either map to a new String, causing allocations, or do .remove and .insert calls on a String, which wouldn’t cause reallocations if you never grow the String, but would cause slowdowns on large strings due to the need to backshift elements on every item.

Here, you can just do

use in_place_string_map::MapInPlace;

fn decode_percent(s: &mut str) -> &mut str {
    let mut m = MapInPlace::new(s);

    while let Some(c) = m.pop() {
        match c {
            '%' => {
                let num = m.pop_chars(2).expect("not enough chars");
                let n = u8::from_str_radix(num, 16).expect("invalid hex");
                m.push(n as char).expect("no more capacity");
            }
            _ => {
                m.push(c).expect("no more capacity");
            }
        }
    }

    m.into_mapped()
}

let mut input = String::from("%54r%61ns %52igh%74%73%21");

assert_eq!(decode_percent(&mut input), "Trans Rights!");

Safety

This library takes care to ensure that the input string is always left in a valid state.

Since core::mem::forget is safe, no code can soundly rely on users to call destructors. The contents of the original borrowed string after any operation is left unspecified generally, but it is guaranteed to always be valid UTF-8.

Structs

MapInPlace	A mutable reference to a str that allows for in-place pushes and pops while maintaining valid UTF-8 at all times.
NoCapacityError	An error indicating that there was no capacity remaining when a push was attempted.