feature: make PtrArray{T}(undef, dims...) an alias for malloc(T, dims...)

README.md

@@ -37,6 +37,17 @@ julia> malloc(Int, 4, 4)
 julia> free(ans)
 ```
 
+It is also possible to construct a `PtrArray` using the usual array constructor interface with `undef`:
+
+```julia-repl
+julia> PtrArray{Float64}(undef, 4, 4)
+4×4 PtrArray{Float64, 2}:
+ 7.01389e-316  7.2e-322    2.0e-323   0.0
+ 0.0           1.294e-321  2.47e-322  0.0
+ 4.2e-322      0.0         2.87e-322  6.37223e-316
+ 5.53e-322     0.0         4.05e-322  4.24399e-314
+```
+
 Benchmarks:
 
 ```julia

src/PtrArrays.jl

@@ -65,6 +65,19 @@ function malloc(::Type{T}, dims::Int...) where T
     PtrArray(Ptr{T}(ptr), dims..., check_dims=false)
 end
 
+function PtrArray{T, N}(::UndefInitializer, dims::Vararg{Int, N}) where {T, N}
+    malloc(T, dims...)
+end
+function PtrArray{T, N}(::UndefInitializer, dims::Tuple{Vararg{Int, N}}) where {T, N}
+    malloc(T, dims...)
+end
+function PtrArray{T}(::UndefInitializer, dims::Vararg{Int}) where {T}
+    malloc(T, dims...)
+end
+function PtrArray{T}(::UndefInitializer, dims::Tuple{Vararg{Int}}) where {T}
+    malloc(T, dims...)
+end
+
 """
     free(p::PtrArray)
 

test/runtests.jl

@@ -61,6 +61,15 @@ end
     free(s)
 end
 
+@testset "undef constructors" begin
+    @test (@inferred PtrArray{Float32}(undef, 3, 3)) isa PtrArray{Float32, 2}
+    @test (@inferred PtrArray{Float32}(undef, (3, 3))) isa PtrArray{Float32, 2}
+    @test (@inferred PtrArray{Float32, 2}(undef, 3, 3)) isa PtrArray{Float32, 2}
+    @test (@inferred PtrArray{Float32, 2}(undef, (3, 3))) isa PtrArray{Float32, 2}
+    @test_throws MethodError PtrArray{Float32, 2}(undef, 3)
+    @test_throws MethodError PtrArray{Float32, 2}(undef, (3,))
+end
+
 function f(x, y)
     z = malloc(Int, x)
     z .= y