a pointer with a hint, without doing a memory allocation

This isn't a starknet question, but raw cairo. is it possible to use a pointer reference like let, and set it to a pointer with a hint, without doing a memory allocation?

looks like the answer is yes, but you do need to assign a reference when you declare a pointer reference with let, but that doesn't alter the memory

e.g.

let s : felt* = cast(ap, felt*)
{
	ids.s = some_other_reference
}

the cast(ap, felt*) does nothing, just satisfies the compiler by having something on the rhs of a let