ambiguity generated by default `copyto!` method

[longemen3000]

this line:

StaticArrays.jl/src/broadcast.jl

Line 65 in 17e8c37

@inline Base.copyto!(dest, B::Broadcasted{<:StaticArrayStyle}) = _copyto!(dest, B)

seems that _copyto! only special handles methods that have static axes. is is correct to assume that those axes only happen on x <: AbstractArray ?. if that is the case, then other type trying to dispatch on copyto! only needs to define:

copyto!(dest::MyType,bc::Base.Broadcsast.AbstractArrayType{N})

then, if an external package needs to define
but the catchall method causes ambiguities in that regard.

I did a test run of StaticArrays on julia 1.8/windows, and removed that method. all tests passed.

[mateuszbaran]

I don't understand, what exactly is the problem with this method? What is x? Could you give a concrete example of an ambiguity?

I did a test run of StaticArrays on julia 1.8/windows, and removed that method. all tests passed.

There would very likely be a performance regression, you'd have to benchmark a few statically sized broadcasts to verify that.

[longemen3000]

I don't understand, what exactly is the problem with this method? What is x? Could you give a concrete example of an ambiguity?

In general, x is any struct that needs to define implace broadcast assignment. in particular, i just tested DataFrames and it is affected:

using StaticArrays, DataFrames
df = DataFrame(A=1:3)
tup = (2,4,6)
sa = SVector(tup)
df .= tup #works
df .= sa #ambiguous method

There would very likely be a performance regression, you'd have to benchmark a few statically sized broadcasts to verify that.

at least in the coverage, that method isn't touched, because there is also:

StaticArrays.jl/src/broadcast.jl

Line 66 in 17e8c37

@inline Base.copyto!(dest::AbstractArray, B::Broadcasted{<:StaticArrayStyle}) = _copyto!(dest, B)

that catches all x<:AbstractArray uses of copyto! and it's the one that is actually used

[mateuszbaran]

I see now, that's actually a good point -- I agree, removing that methods looks like a good idea.

[mateuszbaran]

Fixed by #1098 .