Pointer-stashing generics via `mem::transmute()`

Question

I\'m attempting to write Rust bindings for a C collection library (Judy Arrays [1]) which only provides itself room to store a pointer-width value. My company has a fair am

Answer 1

Instead of transmuting T to usize directly, you can transmute a &T to &usize:

pub fn insert(&mut self, val: T) {
    unsafe {
        let usize_ref: &usize = mem::transmute(&val);
        self.v = *usize_ref;
    }
}

Beware that this may read from an invalid memory location if the size of T is smaller than the size of usize or if the alignment requirements differ. This could cause a segfault. You can add an assertion to prevent this:

assert_eq!(mem::size_of::<T>(), mem::size_of::<usize>());
assert!(mem::align_of::<usize>() <= mem::align_of::<T>());