Sniffing the return type

[Raf]

promote_op is not what you want. _return_type is. Or just Core.Compiler.return_type

Alternatives to `Base.promote_op(op, ::Type...)` for `op::Type`?

The behavior of promote_op was initially intended for some operations between arrays and scalars and for broadcast, but we’ve gradually moved from relying on it. The general strategy in Base when we want to rely on inference for predicting, for example, the element type of an array is the following: Use Core.Inference.return_type or related functions to get an idea of the return type R. If R is concrete, go ahead, use that. If that is not the case and your array is empty, then also use R. Othe…