`axes(bc::Broadcasted)` isnt used in the `materialize`/`instantiate`

[kunzaatko]

The method axes(x) is documented under the broadcasting interface.

Note

It would be nice if the documentation was better. It does not specify when axes is used and it is not definitely specified what the argument type is. (i.e. that it should be <: Broadcasted)

However the method is not used for determining the broadcasting axes. Instead Broadcast.combine_axes is used.

julia/base/broadcast.jl

Lines 312 to 314 in 1269be6

	if bc.axes isa Nothing # Not done via dispatch to make it easier to extend instantiate(::Broadcasted{Style})
	axes = combine_axes(bc.args...)
	else

What is the purpose of axes? (This method

julia/base/broadcast.jl

Lines 238 to 244 in 1269be6

	@inline Base.axes(bc::Broadcasted) = _axes(bc, bc.axes)
	_axes(::Broadcasted, axes::Tuple) = axes
	@inline _axes(bc::Broadcasted, ::Nothing) = combine_axes(bc.args...)
	_axes(bc::Broadcasted{<:AbstractArrayStyle{0}}, ::Nothing) = ()
	@inline Base.axes(bc::Broadcasted{<:Any, <:NTuple{N}}, d::Integer) where N =
	d <= N ? axes(bc)[d] : OneTo(1)

)

Is it used anywhere in the broadcasting pipeline? Shouldn't the combine_axes be axes for the user to be able to specify it?

Anyway, it should be better documented in either case...