Behavior of BroadcastFunction is inconsistent for ranges

[jishnub]

The docstring for Base.BroadcastFunction says that it

Represents the "dotted" version of an operator, which broadcasts the operator over its arguments, so BroadcastFunction(op) is functionally equivalent to (x...) -> (op).(x...).

Except for ranges

julia> f = +
+ (generic function with 190 methods)

julia> Broadcast.BroadcastFunction(f)(2:3, 2:3)
2-element Vector{Int64}:
 4
 6

julia> f.(2:3, 2:3)
4:2:6

The values are still equal, as we may check with

julia> Base.BroadcastFunction(+)(2:3, 2:3) == (2:3) .+ (2:3)
true

however the types are different. The BroadcastFunction(+) version also allocates whereas the .+ version doesn't.

[simeonschaub]

Ah, the problem is that Base.broadcasted_kwsyntax replaces + with a closure, so because ranges only intercept Base.broadcasted(+, ...), .+(...; kwargs...), which is what BroadcastFunction actually calls, doesn't get intercepted:

julia/base/broadcast.jl

Line 1303 in 878e1cd

@inline broadcasted_kwsyntax(f, args...; kwargs...) = broadcasted((args...)->f(args...; kwargs...), args...)

We could just special-case isempty(kwargs) here, which would be a simple enough fix. Alternatively, we can also just remove support for kwargs from BroadcastFunction.

[jishnub]

Perhaps removing support for kwargs would be the right move, as there won't be such surprises with other operators as well. One may construct the closure and pass it to BroadcastFunction if the parent function needs kwargs

[simeonschaub]

I mean, with kwargs, .+(a, b; c=3) would be consistent with BroadcastFunction again.