I would be in favor of renaming the function (publicly, i.e. in the docs) to set_bit. We could deprecate set_index for now with warning (doubt anyone is using it anyway...)

It was changed to set_index because the pattern is more general than just set_bit (i.e. you can use it on generic arrays, rather than just on Bits), so I think it makes more sense to keep it as set_index for generality

I see. In that case, why do we need a separate function? I.e. why is it not covered by set slice with width 1?

Simpler to use when you know you're only interested in one index. For the same reasons in Python we have x[1] versus having to do x[1:2].

Makes sense -- but I would argue x[1] and x[1:2] is the same interface with different arguments (in fact it literally is the function __getitem__).

Maybe we don't need to do this in this change, but seems reasonable to refactor to have the following interface:

"""
* target: Array[N, T]
* value: Union[Array[M, T], T]
* start: UInt[W]

where M < N and W <= clog2(N)
"""
def set(target: Array, value: Union[Type, Array], start: UInt):
    ...

Now that I think about it there are few new concerns here:

• Should this function work with all Arrays and not just Bits? I kind of assumed it did, but looking at the code closer I'm not certain.
• Do we need a width argument? Can it just be inferred from value? If value is an array of the same dimensionality as target then it is a slice set; else if it is of dimensionality one less than value then it is an index set (of course assuming the contained types match up and all).
• In the case start being a constant value, should we optimize for the simple wiring (non-dynamic mux) case?