Uninitialized, uninitialized and Array constructors supporting uninit…

…ialized (#417)

README.md

@@ -187,6 +187,8 @@ Currently, the `@compat` macro supports the following syntaxes:
 
 * Constructors for `Matrix{T}`, `Array{T}`, and `SparseMatrixCSC{T}` from `UniformScaling` ([#24372], [#24657])
 
+* `Uninitialized` and `uninitialized` with corresponding `Array` constructors ([#24652]).
+
 ## Renaming
 
 
@@ -361,4 +363,5 @@ includes this fix. Find the minimum version from there.
 [#24282]: https://github.com/JuliaLang/julia/issues/24282
 [#24372]: https://github.com/JuliaLang/julia/issues/24372
 [#24459]: https://github.com/JuliaLang/julia/issues/24459
+[#24652]: https://github.com/JuliaLang/julia/issues/24652
 [#24657]: https://github.com/JuliaLang/julia/issues/24657

src/Compat.jl

@@ -793,6 +793,29 @@ if VERSION < v"0.7.0-DEV.2543"
     (::Type{Array{T}}){T}(s::UniformScaling, m::Integer, n::Integer) = Matrix{T}(s, m, n)
 end
 
+# 0.7.0-DEV.2581
+@static if !isdefined(Base, :Uninitialized)
+    if VERSION >= v"0.6.0"
+        include_string(@__MODULE__, """
+            struct Uninitialized end
+            Array{T}(::Uninitialized, args...) where {T} = Array{T}(args...)
+            Array{T,N}(::Uninitialized, args...) where {T,N} = Array{T,N}(args...)
+            Vector(::Uninitialized, args...) = Vector(args...)
+            Matrix(::Uninitialized, args...) = Matrix(args...)
+        """)
+    else
+        include_string(@__MODULE__, """
+            immutable Uninitialized end
+            (::Type{Array{T}}){T}(::Uninitialized, args...) = Array{T}(args...)
+            (::Type{Array{T,N}}){T,N}(::Uninitialized, args...) = Array{T,N}(args...)
+            (::Type{Vector})(::Uninitialized, args...) = Vector(args...)
+            (::Type{Matrix})(::Uninitialized, args...) = Matrix(args...)
+        """)
+    end
+    const uninitialized = Uninitialized()
+    export Uninitialized, uninitialized
+end
+
 include("deprecated.jl")
 
 end # module Compat

test/runtests.jl

@@ -895,6 +895,15 @@ let a = [1 0 0; 0 1 0; 0 0 1]
     @test SparseMatrixCSC{Complex128,Int8}(I, 3, 2)::SparseMatrixCSC{Complex128,Int8} == a[:,1:2]
 end
 
+
+# 0.7.0-DEV.2581
+@test isa(Vector(uninitialized, 2), Vector{Any})
+@test isa(Vector{Float64}(uninitialized, 2), Vector{Float64})
+@test isa(Matrix(uninitialized, 2, 2), Matrix{Any})
+@test isa(Matrix{Float64}(uninitialized, 2, 2), Matrix{Float64})
+@test isa(Array{Float64}(uninitialized, 2, 2), Matrix{Float64})
+@test isa(Array{Float64,3}(uninitialized, 2, 2, 2), Array{Float64,3})
+
 if VERSION < v"0.6.0"
     include("deprecated.jl")
 end