This is a postponement issue tracking postponed RFCs in the general area of "functions generic over a constant" or "generic constants" and so forth.

Example use cases for items parameterized by a constant:

• implement a trait for [T; N] for any N
• small vector types (SmallVec<32>)

Example use cases for generic constants:

• initializers like const FOO<T> = SomeType { value: None::<T> }; (const fn can also address this)

Here is a list of relevant RFCs:

• Constants that depend on type parameters in generic code #1062
• RFC: Generic const and static #1520 -- generic const and static
• Allow types to be parameterized by integer (and bool) constant values. #884