Simplify broadcast's eltype promotion mechanism and make it handle mo…

…re cases.

Re-simplify broadcast's eltype promotion mechanism as in JuliaLang#19421. With benefit of JuliaLang#19667, this simplified mechanism should handle additional cases (e.g. closures accepting more than two arguments). Also rename the mechanism more precisely (_broadcast_type -> _broadcast_eltype).

base/broadcast.jl

@@ -269,22 +269,14 @@ end
 @inline broadcast_elwise_op(f, As...) =
     broadcast!(f, similar(Array{promote_eltype_op(f, As...)}, broadcast_indices(As...)), As...)
 
-ftype(f, A) = typeof(f)
-ftype(f, A...) = typeof(a -> f(a...))
-ftype(T::Type, A...) = Type{T}
-typestuple(a) = (Base.@_pure_meta; Tuple{eltype(a)})
-typestuple(T::Type) = (Base.@_pure_meta; Tuple{Type{T}})
-typestuple(a, b...) = (Base.@_pure_meta; Tuple{typestuple(a).types..., typestuple(b...).types...})
-ziptype(A) = typestuple(A)
-ziptype(A, B) = (Base.@_pure_meta; Iterators.Zip2{typestuple(A), typestuple(B)})
-@inline ziptype(A, B, C, D...) = Iterators.Zip{typestuple(A), ziptype(B, C, D...)}
-
-_broadcast_type(f, T::Type, As...) = Base._return_type(f, typestuple(T, As...))
-_broadcast_type(f, A, Bs...) = Base._default_eltype(Base.Generator{ziptype(A, Bs...), ftype(f, A, Bs...)})
+eltypestuple(a) = (Base.@_pure_meta; Tuple{eltype(a)})
+eltypestuple(T::Type) = (Base.@_pure_meta; Tuple{Type{T}})
+eltypestuple(a, b...) = (Base.@_pure_meta; Tuple{eltypestuple(a).types..., eltypestuple(b...).types...})
+_broadcast_eltype(f, A, Bs...) = Base._return_type(f, eltypestuple(A, Bs...))
 
 # broadcast methods that dispatch on the type of the final container
 @inline function broadcast_c(f, ::Type{Array}, A, Bs...)
-    T = _broadcast_type(f, A, Bs...)
+    T = _broadcast_eltype(f, A, Bs...)
     shape = broadcast_indices(A, Bs...)
     iter = CartesianRange(shape)
     if isleaftype(T)

base/promotion.jl

@@ -231,15 +231,13 @@ end
 promote_op(::Any...) = (@_pure_meta; Any)
 function promote_op{S}(f, ::Type{S})
     @_inline_meta
-    Z = Tuple{_default_type(S)}
-    T = _default_eltype(Generator{Z, typeof(f)})
+    T = _return_type(f, Tuple{_default_type(S)})
     isleaftype(S) && return isleaftype(T) ? T : Any
     return typejoin(S, T)
 end
 function promote_op{R,S}(f, ::Type{R}, ::Type{S})
     @_inline_meta
-    Z = Iterators.Zip2{Tuple{_default_type(R)}, Tuple{_default_type(S)}}
-    T = _default_eltype(Generator{Z, typeof(a -> f(a...))})
+    T = _return_type(f, Tuple{_default_type(R), _default_type(S)})
     isleaftype(R) && isleaftype(S) && return isleaftype(T) ? T : Any
     return typejoin(R, S, T)
 end

base/sparse/sparse.jl

@@ -26,7 +26,7 @@ import Base: @get!, acos, acosd, acot, acotd, acsch, asech, asin, asind, asinh,
     rotl90, rotr90, round, scale!, setindex!, similar, size, transpose, tril,
     triu, vec, permute!, map, map!
 
-import Base.Broadcast: _broadcast_type, broadcast_indices
+import Base.Broadcast: _broadcast_eltype, broadcast_indices
 
 export AbstractSparseArray, AbstractSparseMatrix, AbstractSparseVector,
     SparseMatrixCSC, SparseVector, blkdiag, dense, droptol!, dropzeros!, dropzeros,

base/sparse/sparsematrix.jl

@@ -1413,7 +1413,7 @@ function map{Tf,N}(f::Tf, A::SparseMatrixCSC, Bs::Vararg{SparseMatrixCSC,N})
     fofzeros = f(_zeros_eltypes(A, Bs...)...)
     fpreszeros = fofzeros == zero(fofzeros)
     maxnnzC = fpreszeros ? min(length(A), _sumnnzs(A, Bs...)) : length(A)
-    entrytypeC = _broadcast_type(f, A, Bs...)
+    entrytypeC = _broadcast_eltype(f, A, Bs...)
     indextypeC = _promote_indtype(A, Bs...)
     Ccolptr = Vector{indextypeC}(A.n + 1)
     Crowval = Vector{indextypeC}(maxnnzC)
@@ -1443,7 +1443,7 @@ function broadcast{Tf,N}(f::Tf, A::SparseMatrixCSC, Bs::Vararg{SparseMatrixCSC,N
     fofzeros = f(_zeros_eltypes(A, Bs...)...)
     fpreszeros = fofzeros == zero(fofzeros)
     indextypeC = _promote_indtype(A, Bs...)
-    entrytypeC = _broadcast_type(f, A, Bs...)
+    entrytypeC = _broadcast_eltype(f, A, Bs...)
     Cm, Cn = Base.to_shape(Base.Broadcast.broadcast_indices(A, Bs...))
     maxnnzC = fpreszeros ? _checked_maxnnzbcres(Cm, Cn, A, Bs...) : (Cm * Cn)
     Ccolptr = Vector{indextypeC}(Cn + 1)

test/broadcast.jl

@@ -363,7 +363,7 @@ StrangeType18623(x,y) = (x,y)
 let
     f(A, n) = broadcast(x -> +(x, n), A)
     @test @inferred(f([1.0], 1)) == [2.0]
-    g() = (a = 1; Base.Broadcast._broadcast_type(x -> x + a, 1.0))
+    g() = (a = 1; Base.Broadcast._broadcast_eltype(x -> x + a, 1.0))
     @test @inferred(g()) === Float64
 end
 
@@ -373,3 +373,8 @@ end
 @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]]
+
+# Test that broadcast's promotion mechanism handles closures accepting more than one argument
+let f() = (a = 1; Base.Broadcast._broadcast_eltype((x, y) -> x + y + a, 1.0, 1.0))
+    @test @inferred(f()) == Float64
+end