Should zero(::AbstractArray) call fill!?

[tkoolen]

I thought this was just an issue in StaticArrays (JuliaArrays/StaticArrays.jl#428), but the same thing is happening in Base.

Currently:

julia> mutable struct MyNumber
           val::Float64
       end

julia> Base.zero(::Type{MyNumber}) = MyNumber(0.0)

julia> v = zero([MyNumber(1.0), MyNumber(2.0)])
2-element Array{MyNumber,1}:
 MyNumber(0.0)
 MyNumber(0.0)

julia> v[1].val = 1
1

julia> v
2-element Array{MyNumber,1}:
 MyNumber(1.0)
 MyNumber(1.0)

I think this is not desirable for non-isbits types.

[vtjnash]

Duplicate of #29168