change array and range promotion rule not to convert both containers (#…

…22757)

base/array.jl

@@ -403,7 +403,7 @@ convert(::Type{Array{T,n}}, x::Array{T,n}) where {T,n} = x
 convert(::Type{Array{T}}, x::AbstractArray{S,n}) where {T,n,S} = convert(Array{T,n}, x)
 convert(::Type{Array{T,n}}, x::AbstractArray{S,n}) where {T,n,S} = copy!(Array{T,n}(size(x)), x)
 
-promote_rule(::Type{Array{T,n}}, ::Type{Array{S,n}}) where {T,n,S} = Array{promote_type(T,S),n}
+promote_rule(a::Type{Array{T,n}}, b::Type{Array{S,n}}) where {T,n,S} = el_same(promote_type(T,S), a, b)
 
 ## copying iterators to containers
 

base/range.jl

@@ -763,65 +763,78 @@ end
 
 /(x::Number, r::Range) = [ x/y for y=r ]
 
-promote_rule(::Type{UnitRange{T1}},::Type{UnitRange{T2}}) where {T1,T2} =
-    UnitRange{promote_type(T1,T2)}
+# promote eltype if at least one container wouldn't change, otherwise join container types.
+el_same(::Type{T}, a::Type{<:AbstractArray{T,n}}, b::Type{<:AbstractArray{T,n}}) where {T,n}   = a
+el_same(::Type{T}, a::Type{<:AbstractArray{T,n}}, b::Type{<:AbstractArray{S,n}}) where {T,S,n} = a
+el_same(::Type{T}, a::Type{<:AbstractArray{S,n}}, b::Type{<:AbstractArray{T,n}}) where {T,S,n} = b
+el_same(::Type, a, b) = typejoin(a, b)
+
+promote_rule(a::Type{UnitRange{T1}}, b::Type{UnitRange{T2}}) where {T1,T2} =
+    el_same(promote_type(T1,T2), a, b)
 convert(::Type{UnitRange{T}}, r::UnitRange{T}) where {T<:Real} = r
 convert(::Type{UnitRange{T}}, r::UnitRange) where {T<:Real} = UnitRange{T}(r.start, r.stop)
 
-promote_rule(::Type{OneTo{T1}},::Type{OneTo{T2}}) where {T1,T2} =
-    OneTo{promote_type(T1,T2)}
+promote_rule(a::Type{OneTo{T1}}, b::Type{OneTo{T2}}) where {T1,T2} =
+    el_same(promote_type(T1,T2), a, b)
 convert(::Type{OneTo{T}}, r::OneTo{T}) where {T<:Real} = r
 convert(::Type{OneTo{T}}, r::OneTo) where {T<:Real} = OneTo{T}(r.stop)
 
-promote_rule(::Type{UnitRange{T1}}, ::Type{UR}) where {T1,UR<:AbstractUnitRange} =
-    UnitRange{promote_type(T1,eltype(UR))}
+promote_rule(a::Type{UnitRange{T1}}, ::Type{UR}) where {T1,UR<:AbstractUnitRange} =
+    promote_rule(a, UnitRange{eltype(UR)})
 convert(::Type{UnitRange{T}}, r::AbstractUnitRange) where {T<:Real} = UnitRange{T}(first(r), last(r))
 convert(::Type{UnitRange}, r::AbstractUnitRange) = UnitRange(first(r), last(r))
 
 convert(::Type{AbstractUnitRange{T}}, r::AbstractUnitRange{T}) where {T} = r
 convert(::Type{AbstractUnitRange{T}}, r::UnitRange) where {T} = convert(UnitRange{T}, r)
 convert(::Type{AbstractUnitRange{T}}, r::OneTo) where {T} = convert(OneTo{T}, r)
 
-promote_rule(::Type{StepRange{T1a,T1b}},::Type{StepRange{T2a,T2b}}) where {T1a,T1b,T2a,T2b} =
-    StepRange{promote_type(T1a,T2a),promote_type(T1b,T2b)}
+promote_rule(::Type{StepRange{T1a,T1b}}, ::Type{StepRange{T2a,T2b}}) where {T1a,T1b,T2a,T2b} =
+    el_same(promote_type(T1a,T2a),
+            # el_same only operates on array element type, so just promote second type parameter
+            StepRange{T1a, promote_type(T1b,T2b)},
+            StepRange{T2a, promote_type(T1b,T2b)})
 convert(::Type{StepRange{T1,T2}}, r::StepRange{T1,T2}) where {T1,T2} = r
 
-promote_rule(::Type{StepRange{T1a,T1b}},::Type{UR}) where {T1a,T1b,UR<:AbstractUnitRange} =
-    StepRange{promote_type(T1a,eltype(UR)),promote_type(T1b,eltype(UR))}
+promote_rule(a::Type{StepRange{T1a,T1b}}, ::Type{UR}) where {T1a,T1b,UR<:AbstractUnitRange} =
+    promote_rule(a, StepRange{eltype(UR), eltype(UR)})
 convert(::Type{StepRange{T1,T2}}, r::Range) where {T1,T2} =
     StepRange{T1,T2}(convert(T1, first(r)), convert(T2, step(r)), convert(T1, last(r)))
 convert(::Type{StepRange}, r::AbstractUnitRange{T}) where {T} =
     StepRange{T,T}(first(r), step(r), last(r))
+convert(::Type{StepRange{T1,T2} where T1}, r::Range) where {T2} =
+    convert(StepRange{eltype(r),T2}, r)
 
 promote_rule(::Type{StepRangeLen{T1,R1,S1}},::Type{StepRangeLen{T2,R2,S2}}) where {T1,T2,R1,R2,S1,S2} =
-    StepRangeLen{promote_type(T1,T2), promote_type(R1,R2), promote_type(S1,S2)}
+    el_same(promote_type(T1,T2),
+            StepRangeLen{T1,promote_type(R1,R2),promote_type(S1,S2)},
+            StepRangeLen{T2,promote_type(R1,R2),promote_type(S1,S2)})
 convert(::Type{StepRangeLen{T,R,S}}, r::StepRangeLen{T,R,S}) where {T,R,S} = r
 convert(::Type{StepRangeLen{T,R,S}}, r::StepRangeLen) where {T,R,S} =
     StepRangeLen{T,R,S}(convert(R, r.ref), convert(S, r.step), length(r), r.offset)
 convert(::Type{StepRangeLen{T}}, r::StepRangeLen) where {T} =
     StepRangeLen(convert(T, r.ref), convert(T, r.step), length(r), r.offset)
 
-promote_rule(::Type{StepRangeLen{T,R,S}}, ::Type{OR}) where {T,R,S,OR<:Range} =
-    StepRangeLen{promote_type(T,eltype(OR)),promote_type(R,eltype(OR)),promote_type(S,eltype(OR))}
+promote_rule(a::Type{StepRangeLen{T,R,S}}, ::Type{OR}) where {T,R,S,OR<:Range} =
+    promote_rule(a, StepRangeLen{eltype(OR), eltype(OR), eltype(OR)})
 convert(::Type{StepRangeLen{T,R,S}}, r::Range) where {T,R,S} =
     StepRangeLen{T,R,S}(R(first(r)), S(step(r)), length(r))
 convert(::Type{StepRangeLen{T}}, r::Range) where {T} =
     StepRangeLen(T(first(r)), T(step(r)), length(r))
 convert(::Type{StepRangeLen}, r::Range) = convert(StepRangeLen{eltype(r)}, r)
 
-promote_rule(::Type{LinSpace{T1}},::Type{LinSpace{T2}}) where {T1,T2} =
-    LinSpace{promote_type(T1,T2)}
+promote_rule(a::Type{LinSpace{T1}}, b::Type{LinSpace{T2}}) where {T1,T2} =
+    el_same(promote_type(T1,T2), a, b)
 convert(::Type{LinSpace{T}}, r::LinSpace{T}) where {T} = r
 convert(::Type{LinSpace{T}}, r::Range) where {T} =
     LinSpace{T}(first(r), last(r), length(r))
 convert(::Type{LinSpace}, r::Range{T}) where {T} =
     convert(LinSpace{T}, r)
 
-promote_rule(::Type{LinSpace{T}}, ::Type{OR}) where {T,OR<:OrdinalRange} =
-    LinSpace{promote_type(T,eltype(OR))}
+promote_rule(a::Type{LinSpace{T}}, ::Type{OR}) where {T,OR<:OrdinalRange} =
+    promote_rule(a, LinSpace{eltype(OR)})
 
-promote_rule(::Type{LinSpace{L}}, ::Type{StepRangeLen{T,R,S}}) where {L,T,R,S} =
-    StepRangeLen{promote_type(L,T),promote_type(L,R),promote_type(L,S)}
+promote_rule(::Type{LinSpace{L}}, b::Type{StepRangeLen{T,R,S}}) where {L,T,R,S} =
+    promote_rule(StepRangeLen{L,L,L}, b)
 
 # +/- of ranges is defined in operators.jl (to be able to use @eval etc.)
 

test/arrayops.jl

@@ -2177,3 +2177,10 @@ let TT = Union{UInt8, Int8}
     @test a[1] == b[1] == 0x0
     @test a == b
 end
+
+let a = Vector{Int}[[1]],
+    b = Vector{Float64}[[2.0]],
+    c = Vector{Char}[['a']]
+    @test eltype([a;b]) == Vector{Float64}
+    @test eltype([a;c]) == Vector
+end

test/ranges.jl

@@ -632,6 +632,9 @@ end
 @test convert(LinSpace, 0.0:0.1:0.3) === LinSpace{Float64}(0.0, 0.3, 4)
 @test convert(LinSpace, 0:3) === LinSpace{Int}(0, 3, 4)
 
+@test promote('a':'z', 1:2) === ('a':'z', 1:1:2)
+@test eltype(['a':'z', 1:2]) == (StepRange{T,Int} where T)
+
 @test start(LinSpace(0,3,4)) == 1
 @test 2*LinSpace(0,3,4) == LinSpace(0,6,4)
 @test LinSpace(0,3,4)*2 == LinSpace(0,6,4)