Make cu return concrete type if possible

Author: baggepinnen

src/array.jl

@@ -286,7 +286,8 @@ end
 ## utilities
 
 cu(xs) = adapt(CuArray{Float32}, xs)
-cu(::Type{Array{T,N}}) where {T,N} = CuArray{T,N}
+cu(::Type{Array{T,N}}) where {T,N} = CuArray{T,N,Nothing}
+cu(::Type{Array{T}}) where {T} = CuArray{T}
 Base.getindex(::typeof(cu), xs...) = CuArray([xs...])
 
 zeros(T::Type, dims...) = fill!(CuArray{T}(undef, dims...), 0)

test/base.jl

@@ -39,8 +39,8 @@ end
   @test cu(1:3) === 1:3
   @test Base.elsize(xs) == sizeof(Int)
   @test CuArray{Int, 2}(xs) === xs
-  @test cu(Array{Float64,1}) == CuArray{Float64,1}
-  @test cu(Array{Float64,4}) == CuArray{Float64,4}
+  @test cu(Array{Float64,1}) == CuArray{Float64,1, Nothing}
+  @test cu(Array{Float64,4}) == CuArray{Float64,4, Nothing}
   @test cu(Array{Float64}) == CuArray{Float64}
 
   @test_throws ArgumentError Base.unsafe_convert(Ptr{Int}, xs)