Support conversion to AbstractArray (#747)

Julia Base defines conversion to the abstract types AbstractArray{T} and AbstractArray{T,N} by invoking their (abstract) constructors. These fail with an error for static vectors.

This change defines the AbstractArray{T} and AbstractArray{T,N} constructors for static arrays in terms of similar_type.

Author: c42f

src/convert.jl

@@ -11,6 +11,12 @@
 @inline convert(::Type{SA}, sa::SA) where {SA<:StaticArray} = sa
 @inline convert(::Type{SA}, x::Tuple) where {SA<:StaticArray} = SA(x) # convert -> constructor. Hopefully no loops...
 
+# support conversion to AbstractArray
+AbstractArray{T}(sa::StaticArray{S,T}) where {S,T} = sa
+AbstractArray{T,N}(sa::StaticArray{S,T,N}) where {S,T,N} = sa
+AbstractArray{T}(sa::StaticArray{S,U}) where {S,T,U} = similar_type(typeof(sa),T,Size(sa))(sa)
+AbstractArray{T,N}(sa::StaticArray{S,U,N}) where {S,T,U,N} = similar_type(typeof(sa),T,Size(sa))(sa)
+
 # Constructing a Tuple from a StaticArray
 @inline Tuple(a::StaticArray) = unroll_tuple(a, Length(a))
 

test/abstractarray.jl

@@ -129,6 +129,55 @@ using StaticArrays, Test, LinearAlgebra
         m = MVector(1, 2, 3)
         @test @inferred(reverse(m))::typeof(m) == MVector(3, 2, 1)
     end
+
+    @testset "Conversion to AbstractArray" begin
+        # Issue #746
+        # conversion to AbstractArray changes the eltype from Int to Float64
+        sv = SVector(1,2)
+        @test @inferred(convert(AbstractArray{Float64}, sv)) isa SVector{2,Float64}
+        @test @inferred(convert(AbstractVector{Float64}, sv)) isa SVector{2,Float64}
+        @test convert(AbstractArray{Float64}, sv) == sv
+        @test convert(AbstractArray{Int}, sv) === sv
+        sm = SMatrix{2,2}(1,2,3,4)
+        @test @inferred(convert(AbstractArray{Float64,2}, sm)) isa SMatrix{2,2,Float64}
+        @test convert(AbstractArray{Float64,2}, sm) == sm
+        @test convert(AbstractArray{Int,2}, sm) === sm
+        mv = MVector(1, 2, 3)
+        @test @inferred(convert(AbstractArray{Float64}, mv)) isa MVector{3,Float64}
+        @test @inferred(convert(AbstractVector{Float64}, mv)) isa MVector{3,Float64}
+        @test convert(AbstractArray{Float64}, mv) == mv
+        @test convert(AbstractArray{Int}, mv) === mv
+        mm = MMatrix{2, 2}(1, 2, 3, 4)
+        @test @inferred(convert(AbstractArray{Float64,2}, mm)) isa MMatrix{2,2,Float64}
+        @test convert(AbstractArray{Float64,2}, mm) == mm
+        @test convert(AbstractArray{Int,2}, mm) === mm
+
+        # Test some of the types in StaticMatrixLike
+        sym = Symmetric(SA[1 2; 2 3])
+        @test @inferred(convert(AbstractArray{Float64}, sym)) isa Symmetric{Float64,SMatrix{2,2,Float64,4}}
+        @test @inferred(convert(AbstractArray{Float64,2}, sym)) isa Symmetric{Float64,SMatrix{2,2,Float64,4}}
+        @test convert(AbstractArray{Float64}, sym) == sym
+        her = Hermitian(SA[1 2+im; 2-im 3])
+        @test @inferred(convert(AbstractArray{ComplexF64}, her)) isa Hermitian{ComplexF64,SMatrix{2,2,ComplexF64,4}}
+        @test convert(AbstractArray{ComplexF64}, her) == her
+        diag = Diagonal(SVector(1,2))
+        @test @inferred(convert(AbstractArray{Float64}, diag)) isa Diagonal{Float64,SVector{2,Float64}}
+        @test convert(AbstractArray{Float64}, diag) == diag
+        # The following cases currently convert the SMatrix into an MMatrix, because
+        # the constructor in Base invokes `similar`, rather than `convert`, on the static array
+        trans = Transpose(SVector(1,2))
+        @test_broken @inferred(convert(AbstractArray{Float64}, trans)) isa Transpose{Float64,SVector{2,Float64}}
+        adj = Adjoint(SVector(1,2))
+        @test_broken @inferred(convert(AbstractArray{Float64}, adj)) isa Adjoint{Float64,SVector{2,Float64}}
+        uptri = UpperTriangular(SA[1 2; 0 3])
+        @test_broken @inferred(convert(AbstractArray{Float64}, uptri)) isa UpperTriangular{Float64,SMatrix{2,2,Float64,4}}
+        lotri = LowerTriangular(SA[1 0; 2 3])
+        @test_broken @inferred(convert(AbstractArray{Float64}, lotri)) isa LowerTriangular{Float64,SMatrix{2,2,Float64,4}}
+        unituptri = UnitUpperTriangular(SA[1 2; 0 1])
+        @test_broken @inferred(convert(AbstractArray{Float64}, unituptri)) isa UnitUpperTriangular{Float64,SMatrix{2,2,Float64,4}}
+        unitlotri = UnitLowerTriangular(SA[1 0; 2 1])
+        @test_broken @inferred(convert(AbstractArray{Float64}, unitlotri)) isa UnitLowerTriangular{Float64,SMatrix{2,2,Float64,4}}
+    end
 end
 
 @testset "vcat() and hcat()" begin
@@ -191,4 +240,3 @@ end
         @test @inferred(vcat(A, B)) === SMatrix{4, 2}([Matrix(A); Matrix(B)])
     end
 end
-