Views of SArray may use getindex to avoid the SubArray wrapper (#908)

* views of SArray use indexing

* move fn defn to abstractarray.jl

* wrap elements in Scalar

* restrict index types

* allow indexing with SArrays

* views for CartesianIndex, inferred in tests

* bump version to v1.2.0

Author: jishnub

Project.toml

@@ -1,6 +1,6 @@
 name = "StaticArrays"
 uuid = "90137ffa-7385-5640-81b9-e52037218182"
-version = "1.1.3"
+version = "1.2.0"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"

src/abstractarray.jl

@@ -295,3 +295,13 @@ if VERSION >= v"1.6.0-DEV.1334"
         return similar_type(typeof(a), Size(newlen))(Base.rest(Tuple(a), i + 1))
     end
 end
+
+# SArrays may avoid the SubArray wrapper and consequently an additional level of indirection
+# The output may use the broadcasting machinery defined for StaticArrays (see issue #892)
+# wrap elements in Scalar to be consistent with 0D views
+_maybewrapscalar(S::SArray{<:Any,T}, r::T) where {T} = Scalar{T}(r)
+_maybewrapscalar(S, r) = r
+function Base.view(S::SArray, I::Union{Colon, Integer, SOneTo, StaticArray{<:Tuple, Int}, CartesianIndex}...)
+    V = getindex(S, I...)
+    _maybewrapscalar(S, V)
+end

test/SArray.jl

@@ -139,6 +139,16 @@
         @test_throws Exception m[1] = 1
 
         @test Base.dataids(m) === ()
+
+        @test (@inferred view(m, :, :)) === m
+        @test (@inferred view(m, :, 1)) === @SArray [11, 12]
+        @test (@inferred view(m, SVector{2,Int}(1,2), 1)) === @SArray [11, 12]
+        @test (@inferred view(m, SMatrix{2,2,Int}(1,2,3,4))) === m
+        @test (@inferred view(m, SOneTo(2), 1)) === @SArray [11, 12]
+        @test (@inferred view(m, 1, 1)) === Scalar(m[1, 1])
+        @test (@inferred view(m, CartesianIndex(1, 1))) === Scalar(m[1, 1])
+        @test (@inferred view(m, CartesianIndex(1, 1, 1))) === Scalar(m[1, 1])
+        @test (@inferred view(m, 1, 1, CartesianIndex(1))) === Scalar(m[1, 1])
     end
 
     @testset "promotion" begin

test/SVector.jl

@@ -82,6 +82,14 @@
         @test length(v) === 3
 
         @test_throws Exception v[1] = 1
+
+        @test (@inferred view(v, :)) === v
+        @test (@inferred view(v, 1)) === Scalar(v[1])
+        @test (@inferred view(v, CartesianIndex(1))) === Scalar(v[1])
+        @test (@inferred view(v, CartesianIndex(1,1))) === Scalar(v[1])
+        @test (@inferred view(v, 1, CartesianIndex(1))) === Scalar(v[1])
+        @test (@inferred view(v, SVector{2,Int}(1,2))) === @SArray [11, 12]
+        @test (@inferred view(v, SOneTo(2))) === @SArray [11, 12]
     end
 
     @testset "CartesianIndex" begin