Adopt suggestions and add more internal doc/ comments.

Co-Authored-By: Pietro Vertechi <6333339+piever@users.noreply.github.com>

Author: N5N3

src/StructArrays.jl

@@ -30,8 +30,8 @@ import Adapt
 Adapt.adapt_structure(to, s::StructArray) = replace_storage(x->Adapt.adapt(to, x), s)
 
 # for GPU broadcast
-import GPUArraysCore: backend
-function backend(::Type{T}) where {T<:StructArray}
+import GPUArraysCore
+function GPUArraysCore.backend(::Type{T}) where {T<:StructArray}
     backs = map(backend, fieldtypes(array_types(T)))
     all(Base.Fix2(===, backs[1]), tail(backs)) || error("backend mismatch!")
     return backs[1]

src/interface.jl

@@ -52,3 +52,9 @@ end
 createinstance(::Type{T}, args...) where {T<:Tup} = T(args)
 
 createinstance(::Type{T}) where {T} = (x...) -> createinstance(T, x...)
+
+struct Instantiator{T} end
+
+Instantiator(::Type{T}) where {T} = Instantiator{T}()
+
+(::Instantiator{T})(args...) where {T} = createinstance(T, args...)

src/staticarrays_support.jl

@@ -35,23 +35,32 @@ function Broadcast.instantiate(bc::Broadcasted{StructStaticArrayStyle{M}}) where
     bc′ = Broadcast.instantiate(replace_structarray(bc))
     return convert(Broadcasted{StructStaticArrayStyle{M}}, bc′)
 end
-# This looks costy, but compiler should be able to optimize them away
+# This looks costly, but the compiler should be able to optimize them away
 Broadcast._axes(bc::Broadcasted{<:StructStaticArrayStyle}, ::Nothing) = axes(replace_structarray(bc))
 
 to_staticstyle(@nospecialize(x::Type)) = x
 to_staticstyle(::Type{StructStaticArrayStyle{N}}) where {N} = StaticArrayStyle{N}
+
+"""
+    replace_structarray(bc::Broadcasted)
+
+An internal function transforms the `Broadcasted` with `StructArray` into
+an equivalent one without it. This is not a must if the root `BroadcastStyle`
+supports `AbstractArray`. But some `BroadcastStyle` limits the input array types, 
+e.g. `StaticArrayStyle`, thus we have to omit all `StructArray`.
+"""
 function replace_structarray(bc::Broadcasted{Style}) where {Style}
     args = replace_structarray_args(bc.args)
     return Broadcasted{to_staticstyle(Style)}(bc.f, args, nothing)
 end
 function replace_structarray(A::StructArray)
-    f = createinstance(eltype(A))
+    f = Instantiator(eltype(A))
     args = Tuple(components(A))
     return Broadcasted{StaticArrayStyle{ndims(A)}}(f, args, nothing)
 end
 replace_structarray(@nospecialize(A)) = A
 
-replace_structarray_args(args::Tuple) = (replace_structarray(args[1]), replace_structarray_args(Base.tail(args))...)
+replace_structarray_args(args::Tuple) = (replace_structarray(args[1]), replace_structarray_args(tail(args))...)
 replace_structarray_args(::Tuple{}) = ()
 
 # StaticArrayStyle has no similar defined.

test/runtests.jl

@@ -1091,6 +1091,19 @@ Adapt.adapt_storage(::ArrayConverter, xs::AbstractArray) = convert(Array, xs)
     @test t.b.d isa Array
 end
 
+# The following code defines `MyArray1/2/3` with different `BroadcastStyle`s.
+# 1. `MyArray1` and `MyArray1` have `similar` defined.
+#     We use them to simulate `BroadcastStyle` overloading `Base.copyto!`.
+# 2. `MyArray3` has no `similar` defined. 
+#    We use it to simulate `BroadcastStyle` overloading `Base.copy`.
+# 3. Their resolved style could be summaryized as (`-` means conflict)
+#              |  MyArray1  |  MyArray2  |  MyArray3  |  Array
+#    -------------------------------------------------------------
+#    MyArray1  |  MyArray1  |      -     |  MyArray1  |  MyArray1
+#    MyArray2  |      -     |  MyArray2  |      -     |  MyArray2
+#    MyArray3  |  MyArray1  |      -     |  MyArray3  |  MyArray3
+#    Array     |  MyArray1  |  Array     |  MyArray3  |  Array
+
 for S in (1, 2, 3)
     MyArray = Symbol(:MyArray, S)
     @eval begin
@@ -1129,9 +1142,9 @@ Base.BroadcastStyle(::Broadcast.ArrayStyle{MyArray2}, S::Broadcast.DefaultArrayS
     @test isa(@inferred(Base.dataids(s)), NTuple{N, UInt} where {N})
 
     # Make sure we can handle style with similar defined
-    # And we can handle most conflict
-    # s1 and s2 has similar defined, but s3 not
-    # s2 are conflict with s1 and s3. (And it's weaker than DefaultArrayStyle)
+    # And we can handle most conflicts
+    # `s1` and `s2` have similar defined, but `s3` does not
+    # `s2` conflicts with `s1` and `s3` and is weaker than `DefaultArrayStyle`
     s1 = StructArray{ComplexF64}((MyArray1(rand(2)), MyArray1(rand(2))))
     s2 = StructArray{ComplexF64}((MyArray2(rand(2)), MyArray2(rand(2))))
     s3 = StructArray{ComplexF64}((MyArray3(rand(2)), MyArray3(rand(2))))