I think I understand what const generics are. But I fail to see a use case for it, other than using them in array literals and abstractions over arrays.
Can you share you your use case?
Can you share you your use case?
1) Create a Vec (separate allocation)
2) Make 1024 or 1048576 a global constant that every relevant struct and function references directly (whole program must use the same size at once; forget about exposing it as a library)
With const generics I can make all that code generic over the buffer resolution, meaning I can trivially use multiple different versions within the same build, without doing extra allocations, and I could even expose that code as a library for others to use at whatever resolution they wish
Does rust have compile time protection against stack overflow? (... and what about recursion? is the stack dynamically resized at runtime?)
For example: what if I decide at some point to create a Vec of this struct? I don't want each of those elements then also putting their internal buffers into separate allocations on the heap, when the Vec itself is already on the heap. I want the struct to be as "flat" as possible, and to only allocate for the sake of the stack as a final step when the use-case demands it
Recursion can blow your stack.
I could very easily make the word size generic, but not the depth. So I either had to make the depth dynamic (pretty expensive if you have hundreds of thousands of FIFO operations per second) or hack around it somehow.
Now I can just make the depth a generic parameter.
You can also abuse these types of generics to force the compiler to generate specialized versions of some methods in order to get better performance (at the cost of binary size) without having to manually create a bunch of variants of the same code.
With const generics, the library provided implementations for all `[T; N]`, so my code worked out of the box with no headache.
Well, array literals are very convenient in some areas.
Matrix types can be cleaned up across projects, one widespread area being 3d graphics. Previously, you either had to create a separate type for each matrix size, or use a backing vector (of vectors); the first solution is ugly (because of redundancy), the second is potentially underperformant (in cases where one wants to avoid dynamic allocations as much as possible).