Module index_ext::mem[−][src]

Expand description

Integer wrappers that are constrained to the range of usize or isize.

This module defines a number of wrappers around the basic integer types which ensure that the stored value can be trivially converted to a usize without loss of data. That is these types offer a getter that converts the number with as usize but otherwise they are ABI compatible with their underlying integer type.

Usage

These are best used in places where the ABI or layout of the type is important but there is a security risk associated with having to write (fallible) conversions all the time. Consider the case of a matrix where dimensions are stored as u32 for compatibility reasons. We would now like to allocate a buffer for it which requires calculating the number of elements as a u64 and then convert to usize. However, no matter in which number type you intend to store the result you lose semantic meaning because there is no ‘proof’ attached to the value that it will also fit into the other value range.

use index_ext::mem::Umem64;

struct Matrix {
    width: u32,
    height: u32,
}

let elements = u64::from(mat.width) * u64::from(mat.height);
let length: Umem64 = Umem64::new(elements)?;

let matrix = vec![0; length.get()];