Indeed, I can't wait for const generics to become available outside of std, I've been bumping into that limitation since pre-rust-1.0 days, it'll be amazing to finally be able to rewrite all that hacky code correctly.
you can't pass it a slice. This would let you pass a vector to this function.
Now, because this wasn't possible previously, it means many things take a slice, and then check that the length is the length they expect, because that ends up being easier for folks. Stuff like this helps it be able to be done properly.
(This specific function is one example that is done in this style, and it's a pain. I have real world code that looks like
let foo = u16::from_be_bytes([some_slice[0], some_slice[1]]);
This gets even worse with say, u128::from_be_bytes.)
steveklabnik is (of course) correct, but you also have to consider the performance cost of a dynamicaly sized slice versus a statically sized array.
A situation I've encountered several times already is implementing statically sized FIFOs. At the moment in Rust I can't implement a type "FIFO of depth N" where is a generic, static parameter. My only choices are implementing "FIFO of depth n" where n is provided dynamically at runtime (and implemented internally using something like a VecDeque) or a completely fixed depth FIFO type that I need to duplicate for every depth (FIFO32, FIFO16, FIFO10 etc...).
If you require very high performance a dynamically checked FIFO can incur a fairly large overhead when a well optimized static FIFO can implement most operations in a couple of opcodes at most.
and then back it with an array. I learned this trick from whitequark.
(Though maybe if you want something other than a slice of bytes, this gets harder... I've used this trick for ringbuffers/mmio only, personally, so YMMV.)
That being said real const generics will make this way nicer, eventually.
I wasn't aware of this trick, thank you for that. I guess if I have to implement another FIFO before const generics land I'll have an opportunity to try it out...
I don’t think so - you can only use static functions to declare static variables. But you could do it with a macro. It’s debatable whether that would be readable and predictable, though.