fix: ArrayPartition arithmetic type-stability

Author: AayushSabharwal

src/array_partition.jl

@@ -153,11 +153,11 @@ for op in (:*, :/)
 end
 
 function Base.:*(A::Number, B::ArrayPartition)
-    ArrayPartition(map(y -> Base.broadcast(*, A, y), B.x))
+    ArrayPartition(map(y -> A .* y, B.x))
 end
 
 function Base.:\(A::Number, B::ArrayPartition)
-    ArrayPartition(map(y -> Base.broadcast(/, y, A), B.x))
+    B / A
 end
 
 Base.:(==)(A::ArrayPartition, B::ArrayPartition) = A.x == B.x
@@ -284,7 +284,7 @@ recursive_eltype(A::ArrayPartition) = recursive_eltype(first(A.x))
 Base.iterate(A::ArrayPartition) = iterate(Chain(A.x))
 Base.iterate(A::ArrayPartition, state) = iterate(Chain(A.x), state)
 
-Base.length(A::ArrayPartition) = sum((length(x) for x in A.x))
+Base.length(A::ArrayPartition) = sum(broadcast(length, A.x))
 Base.size(A::ArrayPartition) = (length(A),)
 
 # redefine first and last to avoid slow and not type-stable indexing
@@ -323,21 +323,13 @@ function Broadcast.BroadcastStyle(::ArrayPartitionStyle,
     Broadcast.DefaultArrayStyle{N}()
 end
 
-combine_styles(args::Tuple{}) = Broadcast.DefaultArrayStyle{0}()
-@inline function combine_styles(args::Tuple{Any})
-    Broadcast.result_style(Broadcast.BroadcastStyle(args[1]))
-end
-@inline function combine_styles(args::Tuple{Any, Any})
-    Broadcast.result_style(Broadcast.BroadcastStyle(args[1]),
-        Broadcast.BroadcastStyle(args[2]))
-end
-@inline function combine_styles(args::Tuple)
-    Broadcast.result_style(Broadcast.BroadcastStyle(args[1]),
-        combine_styles(Base.tail(args)))
+@generated function combine_styles(t)
+    @show t
+    return :($(reduce(Broadcast.result_style, Broadcast.BroadcastStyle.(t.parameters[1].parameters))))
 end
 
 function Broadcast.BroadcastStyle(::Type{ArrayPartition{T, S}}) where {T, S}
-    Style = combine_styles((S.parameters...,))
+    Style = combine_styles(S)
     ArrayPartitionStyle(Style)
 end