#box #map #allocation #re-using

map_box

Map the value in a Box, re-using the allocation when possible

1 unstable release

0.2.2 Feb 2, 2024
0.2.1 Feb 2, 2024
0.2.0 Feb 2, 2024
0.1.1 Feb 2, 2024
0.1.0 Feb 2, 2024

#269 in Memory management

29 downloads per month

MIT license

8KB
136 lines

Map Box

githubcrates-iodocs-rs

Map the value in a Box, re-using the allocation when possible.

For example, this code will not re-allocate.

use map_box::Map;

let b = Box::new(42u64);
let b = b.map_box(|v| v as i64);

The signature of map is:

impl<T1> Box<T1> {
    fn map_box<T2>(self, f: impl FnMut(T1) -> T2) -> Box<T2>;
}

Limitations

If the alignment requirements of the type changes, even if the alignment becomes lower, the Box needs to be reallocated. This is because:

  1. alloc::dealloc requires the layout to be identical to the layout that the allocation was made with
  2. alloc::realloc only takes a new size, it cannot change the layout of the allocation downwards

No runtime deps