implement ConstructionBase interface

Project.toml

@@ -3,13 +3,15 @@ uuid = "90137ffa-7385-5640-81b9-e52037218182"
 version = "1.5.6"
 
 [deps]
+ConstructionBase = "187b0558-2788-49d3-abe0-74a17ed4e7c9"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 StaticArraysCore = "1e83bf80-4336-4d27-bf5d-d5a4f845583c"
 Statistics = "10745b16-79ce-11e8-11f9-7d13ad32a3b2"
 
 [compat]
 julia = "1.6"
+ConstructionBase = "1"
 StaticArraysCore = "~1.3.0"
 
 [extras]

src/StaticArrays.jl

@@ -10,6 +10,8 @@ import Base: getindex, setindex!, size, similar, vec, show, length, convert, pro
 
 import Statistics: mean
 
+import ConstructionBase: constructorof
+
 using Random
 import Random: rand, randn, randexp, rand!, randn!, randexp!
 using Core.Compiler: return_type
@@ -128,6 +130,7 @@ include("svd.jl")
 include("qr.jl")
 include("deque.jl")
 include("flatten.jl")
+include("constructorof.jl")
 include("io.jl")
 include("pinv.jl")
 

src/constructorof.jl

@@ -0,0 +1,9 @@
+# keep the size when reconstructing arrays
+# eltype can be different
+constructorof(sa::Type{<:SArray{S}}) where {S} = SArray{S}
+constructorof(sa::Type{<:MArray{S}}) where {S} = MArray{S}
+
+# don't keep neither size nor eltype for vectors:
+# both are unambiguously determined by the values
+constructorof(::Type{<:SVector}) = SVector
+constructorof(::Type{<:MVector}) = MVector

test/constructorof.jl

@@ -0,0 +1,25 @@
+using StaticArrays
+using Test
+using ConstructionBase: constructorof
+
+@testset "constructorof" begin
+    sa = @SVector [2, 4, 6, 8]
+    sa2 = constructorof(typeof(sa))((3.0, 5.0, 7.0, 9.0))
+    @test sa2 === @SVector [3.0, 5.0, 7.0, 9.0]
+
+    ma = @MMatrix [2.0 4.0; 6.0 8.0]
+    ma2 = constructorof(typeof(ma))((1, 2, 3, 4))
+    @test ma2 isa MArray{Tuple{2,2},Int,2,4}
+    @test all(ma2 .=== @MMatrix [1 3; 2 4])
+
+    for T in (SVector, MVector)
+        @test constructorof(T)((1, 2, 3))::T == T((1, 2, 3))
+        @test constructorof(T{3})((1, 2, 3))::T == T((1, 2, 3))
+        @test constructorof(T{3})((1, 2))::T == T((1, 2))
+        @test constructorof(T{3, Symbol})((1, 2, 3))::T == T((1, 2, 3))
+        @test constructorof(T{3, Symbol})((1, 2))::T == T((1, 2))
+        @test constructorof(T{3, X} where {X})((1, 2, 3))::T == T((1, 2, 3))
+        @test constructorof(T{3, X} where {X})((1, 2))::T == T((1, 2))
+        @test constructorof(T{X, Symbol} where {X})((1, 2, 3))::T == T((1, 2, 3))
+    end
+end

test/runtests.jl

@@ -78,6 +78,7 @@ if TEST_GROUP ∈ ["", "all", "group-B"]
     addtests("chol.jl") # hermitian_type(::Type{Any}) for block algorithm
     addtests("deque.jl")
     addtests("flatten.jl")
+    addtests("constructorof.jl")
     addtests("io.jl")
     addtests("svd.jl")
 end