There are times when indices need to be tightly packed (mesh geometry for example), where its useful to store indices as u32 instead of usize.
Is there a way to index a vector in Rust without having to explicitly cast to usize every time? eg:
vector[some_u32 as usize];
Casting in single instances isn't a problem, its just tedious when needed frequently.
Is there a way to avoid having to cast here?
No.
If it were your own type, you could implement Index<u32>, but it isn't and you can't.
If you're really, pathologically opposed to casting the index, you could write an adaptor type that does the cast, but that's getting a bit silly.
If you only want to index arrays of your own type, and you use a newtype for the index, then you can create an Index impl:
struct MyIndex(u32);
struct MyValue(u64);
impl std::ops::Index<MyIndex> for [MyValue] {
type Output = MyValue;
fn index(&self, idx: MyIndex) -> &MyValue {
&self[idx.0 as usize]
}
}
Now, you can index any array of MyValues with MyIndex. Instead of using u32 everywhere, you now have to use MyIndex. There's the newtype_derive crate to help you make the MyIndex behave mostly like a u32.
