Broadcasting with Float ArrayPartition

[HadrienNU]

I have an issue with broadcasting when the array partition is composed of Float64

julia> x = ArrayPartition(1.0,0.0);

julia> y=zero(x);

julia> y.=x
ERROR: MethodError: no method matching copyto!(::Float64, ::Base.Broadcast.Broadcasted{Base.Broadcast.DefaultArrayStyle{0}, Nothing, typeof(identity), Tuple{Float64}})
Closest candidates are:
  copyto!(::Any, ::ArrayLayouts.Lmul) at ~/.julia/packages/ArrayLayouts/A7uk9/src/lmul.jl:75
  copyto!(::Any, ::ArrayLayouts.Rmul) at ~/.julia/packages/ArrayLayouts/A7uk9/src/lmul.jl:77
  copyto!(::Any, ::ArrayLayouts.Mul) at ~/.julia/packages/ArrayLayouts/A7uk9/src/mul.jl:127
  ...
Stacktrace:
 [1] f
   @ ~/.julia/packages/RecursiveArrayTools/w8ctF/src/array_partition.jl:372 [inlined]
 [2] ntuple
   @ ./ntuple.jl:49 [inlined]
 [3] copyto!
   @ ~/.julia/packages/RecursiveArrayTools/w8ctF/src/array_partition.jl:374 [inlined]
 [4] materialize!
   @ ./broadcast.jl:871 [inlined]
 [5] materialize!(dest::ArrayPartition{Float64, Tuple{Float64, Float64}}, bc::Base.Broadcast.Broadcasted{RecursiveArrayTools.ArrayPartitionStyle{Base.Broadcast.DefaultArrayStyle{0}}, Nothing, typeof(identity), Tuple{ArrayPartition{Float64, Tuple{Float64, Float64}}}})
   @ Base.Broadcast ./broadcast.jl:868
 [6] top-level scope
   @ REPL[39]:1

Indeed, when testing for typeof(x) <: AbstractArray it returns true and some codes assume that dot syntax is fine.
In my case, when trying to do ensemble simulation with ArrayPartition. The analysis at https://github.com/SciML/SciMLBase.jl/blob/master/src/ensemble/ensemble_analysis.jl#L209 assumes it can safely use dot syntax and then raise the error.

[ChrisRackauckas]

If you have an immutable state, i.e. a tuple of scalars instead of vectors, you cannot mutate. That's pretty standard and StaticArrays acts the same way. Maybe this can have a better error message but I'm not sure how it would act otherwise, since the objects are immutable by the user's choice in this scenario.

[HadrienNU]

Got it, that an issue I should open more on the specific code that raise the error then. Thanks.