Make Ref behave as a 0-dimensional array in broadcast

NEWS.md

@@ -47,6 +47,9 @@ This section lists changes that do not have deprecation warnings.
     `broadcast` calls (see above) and produce an `Array`.  If you want
     a `Range` result, use `+` and `*`, etcetera ([#17623]).
 
+  * `broadcast` now treats `Ref` (except for `Ptr`) arguments as 0-dimensional
+    arrays ([#18965]).
+
 Library improvements
 --------------------
 
@@ -749,6 +752,7 @@ Language tooling improvements
 [#18628]: https://github.com/JuliaLang/julia/issues/18628
 [#18839]: https://github.com/JuliaLang/julia/issues/18839
 [#18931]: https://github.com/JuliaLang/julia/issues/18931
+[#18965]: https://github.com/JuliaLang/julia/issues/18965
 [#18977]: https://github.com/JuliaLang/julia/issues/18977
 [#19018]: https://github.com/JuliaLang/julia/issues/19018
 [#19233]: https://github.com/JuliaLang/julia/issues/19233

base/broadcast.jl

@@ -27,7 +27,9 @@ end
 # logic for deciding the resulting container type
 containertype(x) = containertype(typeof(x))
 containertype(::Type) = Any
+containertype{T<:Ptr}(::Type{T}) = Any
 containertype{T<:Tuple}(::Type{T}) = Tuple
+containertype{T<:Ref}(::Type{T}) = Array
 containertype{T<:AbstractArray}(::Type{T}) = Array
 containertype(ct1, ct2) = promote_containertype(containertype(ct1), containertype(ct2))
 @inline containertype(ct1, ct2, cts...) = promote_containertype(containertype(ct1), containertype(ct2, cts...))
@@ -46,6 +48,7 @@ broadcast_indices(A) = broadcast_indices(containertype(A), A)
 broadcast_indices(::Type{Any}, A) = ()
 broadcast_indices(::Type{Tuple}, A) = (OneTo(length(A)),)
 broadcast_indices(::Type{Array}, A) = indices(A)
+broadcast_indices(::Type{Array}, A::Ref) = ()
 @inline broadcast_indices(A, B...) = broadcast_shape((), broadcast_indices(A), map(broadcast_indices, B)...)
 # shape (i.e., tuple-of-indices) inputs
 broadcast_shape(shape::Tuple) = shape
@@ -118,6 +121,7 @@ map_newindexer(shape, ::Tuple{}) = (), ()
 end
 
 Base.@propagate_inbounds _broadcast_getindex(A, I) = _broadcast_getindex(containertype(A), A, I)
+Base.@propagate_inbounds _broadcast_getindex(::Type{Array}, A::Ref, I) = A[]
 Base.@propagate_inbounds _broadcast_getindex(::Type{Any}, A, I) = A
 Base.@propagate_inbounds _broadcast_getindex(::Any, A, I) = A[I]
 
@@ -301,15 +305,16 @@ end
 """
     broadcast(f, As...)
 
-Broadcasts the arrays, tuples and/or scalars `As` to a container of the
+Broadcasts the arrays, tuples, `Ref` and/or scalars `As` to a container of the
 appropriate type and dimensions. In this context, anything that is not a
-subtype of `AbstractArray` or `Tuple` is considered a scalar. The resulting
-container is established by the following rules:
+subtype of `AbstractArray`, `Ref` (except for `Ptr`s) or `Tuple` is considered
+a scalar. The resulting container is established by the following rules:
 
  - If all the arguments are scalars, it returns a scalar.
  - If the arguments are tuples and zero or more scalars, it returns a tuple.
- - If there is at least an array in the arguments, it returns an array
-   (and treats tuples as 1-dimensional arrays) expanding singleton dimensions.
+ - If there is at least an array or a `Ref` in the arguments, it returns an array
+   (and treats any `Ref` as a 0-dimensional array of its contents and any tuple
+   as a 1-dimensional array) expanding singleton dimensions.
 
 A special syntax exists for broadcasting: `f.(args...)` is equivalent to
 `broadcast(f, args...)`, and nested `f.(g.(args...))` calls are fused into a
@@ -351,11 +356,16 @@ julia> abs.((1, -2))
 julia> broadcast(+, 1.0, (0, -2.0))
 (1.0,-1.0)
 
-julia> broadcast(+, 1.0, (0, -2.0), [1])
+julia> broadcast(+, 1.0, (0, -2.0), Ref(1))
 2-element Array{Float64,1}:
  2.0
  0.0
 
+julia> (+).([[0,2], [1,3]], Ref{Vector{Int}}([1,-1]))
+2-element Array{Array{Int64,1},1}:
+ [1,1]
+ [2,2]
+
 julia> string.(("one","two","three","four"), ": ", 1:4)
 4-element Array{String,1}:
  "one: 1"

doc/src/manual/arrays.md

@@ -475,7 +475,7 @@ is equivalent to `broadcast(f, args...)`, providing a convenient syntax to broad
 [automatically fuse](@ref man-dot-operators) into a single `broadcast` call.
 
 Additionally, [`broadcast()`](@ref) is not limited to arrays (see the function documentation),
-it also handles tuples and treats any argument that is not an array or a tuple as a "scalar".
+it also handles tuples and treats any argument that is not an array, tuple or `Ref` (except for `Ptr`) as a "scalar".
 
 ```julia
 julia> convert.(Float32, [1, 2])

test/broadcast.jl

@@ -366,3 +366,10 @@ let
     g() = (a = 1; Base.Broadcast._broadcast_type(x -> x + a, 1.0))
     @test @inferred(g()) === Float64
 end
+
+# Ref as 0-dimensional array for broadcast
+@test (-).(C_NULL, C_NULL)::UInt == 0
+@test (+).(1, Ref(2)) == fill(3)
+@test (+).(Ref(1), Ref(2)) == fill(3)
+@test (+).([[0,2], [1,3]], [1,-1]) == [[1,3], [0,2]]
+@test (+).([[0,2], [1,3]], Ref{Vector{Int}}([1,-1])) == [[1,1], [2,2]]