From 38b85d9fb0be795f73c0bd0ab03c077d55cf6139 Mon Sep 17 00:00:00 2001
From: janEbert <janpublicebert@posteo.net>
Date: Sun, 6 Oct 2019 14:11:22 +0200
Subject: [PATCH] Add `empty` for `AbstractArray`s and their types

`empty` now works on all `AbstractArray`s and the corresponding call
using `Type{<:AbstractArray}`.
The method specialized on `AbstractVector` remains for inlining
purposes.
---
 base/abstractarray.jl |  9 +++++++--
 test/abstractarray.jl | 12 ++++++++++++
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/base/abstractarray.jl b/base/abstractarray.jl
index 62547c8d7e01b..c281109c657c9 100644
--- a/base/abstractarray.jl
+++ b/base/abstractarray.jl
@@ -672,9 +672,10 @@ similar(::Type{T}, shape::Tuple{Union{Integer, OneTo}, Vararg{Union{Integer, One
 similar(::Type{T}, dims::Dims) where {T<:AbstractArray} = T(undef, dims)
 
 """
-    empty(v::AbstractVector, [eltype])
+    empty(a::AbstractArray, [eltype])
+    empty(a::Type{AbstractArray}, [eltype])
 
-Create an empty vector similar to `v`, optionally changing the `eltype`.
+Create an empty array similar to `a`, optionally changing the `eltype`.
 
 # Examples
 
@@ -687,6 +688,10 @@ julia> empty([1.0, 2.0, 3.0], String)
 ```
 """
 empty(a::AbstractVector{T}, ::Type{U}=T) where {T,U} = Vector{U}()
+function empty(a::Type{<:AbstractArray{T,N}}, ::Type{U}=T) where {T,N,U}
+    convert(AbstractArray{U}, a(undef, Tuple(Iterators.repeated(0,N))))
+end
+empty(a::AbstractArray{T}, ::Type{U}=T) where {T,U} = empty(typeof(a), U)
 
 # like empty, but should return a mutable collection, a Vector by default
 emptymutable(a::AbstractVector{T}, ::Type{U}=T) where {T,U} = Vector{U}()
diff --git a/test/abstractarray.jl b/test/abstractarray.jl
index bf6c0f78a30ab..f40d129529837 100644
--- a/test/abstractarray.jl
+++ b/test/abstractarray.jl
@@ -892,11 +892,23 @@ end
     v = [1, 2, 3]
     v2 = empty(v)
     v3 = empty(v, Float64)
+    v4 = empty(typeof(v))
+    v5 = empty(typeof(v), Float64)
     @test !isempty(v)
     empty!(v)
     @test isempty(v)
     @test isempty(v2::Vector{Int})
     @test isempty(v3::Vector{Float64})
+    @test isempty(v4::Vector{Int})
+    @test isempty(v5::Vector{Float64})
+
+    m = [1 2; 3 4]
+    # These call `empty(typeof(m))`, so we don't test that case.
+    m2 = empty(m)
+    m3 = empty(m, Float64)
+    @test !isempty(m)
+    @test isempty(m2::Matrix{Int})
+    @test isempty(m3::Matrix{Float64})
 end
 
 @testset "CartesianIndices" begin