map_in_place
Reuse allocations when converting the elements of a vector, boxed slice or box to a compatible type.
To map in place the types must have identical alignment and size. For vectors the size of in can also be a multiple of the size of out because it can change the capacity. (but out can never be bigger than in).
The *_in_place() methods will panic if the types are not compatible,
while the others will fall back to iterating and collecting.
Example
extern crate map_in_place;
use map_in_place::MapVecInPlace;
fn main() {
let v = vec![8_u32,29,14,5];
let v = v.filter_map(|n| if n < 10 {Some( (n as u8+b'0') as char)}
else {None}
);// happens in place
assert_eq!(&v, &['8','5']);
let v = v.map(|c| c as u8);// falls back to iterators
assert_eq!(&v[..], &b"85"[..]);
}Why all those restrictions?
The Rust allocation interface is a bit more complex than the standard C one of
malloc(size_t) and free(void*):
First, alloc() and dealloc() takes the alignment of the types you want to store,
and allocating with one alignment and freeing with another is undefined behaviour.
Second, Rust requires the owner to know the size of the memory to free, which means one of the types' size must be a multiple of the other, since the capacity is an integer.
License
Licensed under either of
- Apache License, Version 2.0, (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
- MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)
at your option.
Contribution
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.