Strides for Adjoint & Transpose (#710)

README.md

@@ -55,6 +55,8 @@ changes in `julia`.
 
 ## Supported features
 
+* `strides` is defined for Adjoint and Transpose ([#35929]). (since Compat 3.14)
+
 * `Compat.get_num_threads()` adds the functionality of `LinearAlgebra.BLAS.get_num_threads()`, and has matching `Compat.set_num_threads(n)` ([#36360]). (since Compat 3.13.0)
 
 * `@inferred [AllowedType] f(x)` is defined ([#27516]). (since Compat 3.12.0)
@@ -177,3 +179,4 @@ Note that you should specify the correct minimum version for `Compat` in the
 [#35577]: https://github.com/JuliaLang/julia/pull/35577
 [#27516]: https://github.com/JuliaLang/julia/pull/27516
 [#36360]: https://github.com/JuliaLang/julia/pull/36360
+[#35929]: https://github.com/JuliaLang/julia/pull/35929

src/Compat.jl

@@ -414,6 +414,31 @@ if VERSION < v"1.5.0-DEV.681"
     Base.union(r::Base.OneTo, s::Base.OneTo) = Base.OneTo(max(r.stop,s.stop))
 end
 
+# https://github.com/JuliaLang/julia/pull/35929
+# and also https://github.com/JuliaLang/julia/pull/29135 -> Julia 1.5
+if VERSION < v"1.5.0-rc1.13" || v"1.6.0-" < VERSION < v"1.6.0-DEV.323"
+
+    # Compat.stride not Base.stride, so as not to overwrite the method, and not to create ambiguities:
+    function stride(A::AbstractArray, k::Integer)
+        st = strides(A)
+        k ≤ ndims(A) && return st[k]
+        return sum(st .* size(A))
+    end
+    stride(A,k) = Base.stride(A,k) # Fall-through for other methods.
+
+    # These were first defined for Adjoint{...,StridedVector} etc in #29135
+    Base.strides(A::Adjoint{<:Real, <:AbstractVector}) = (stride(A.parent, 2), stride(A.parent, 1))
+    Base.strides(A::Transpose{<:Any, <:AbstractVector}) = (stride(A.parent, 2), stride(A.parent, 1))
+    Base.strides(A::Adjoint{<:Real, <:AbstractMatrix}) = reverse(strides(A.parent))
+    Base.strides(A::Transpose{<:Any, <:AbstractMatrix}) = reverse(strides(A.parent))
+    Base.unsafe_convert(::Type{Ptr{T}}, A::Adjoint{<:Real, <:AbstractVecOrMat}) where {T} = Base.unsafe_convert(Ptr{T}, A.parent)
+    Base.unsafe_convert(::Type{Ptr{T}}, A::Transpose{<:Any, <:AbstractVecOrMat}) where {T} = Base.unsafe_convert(Ptr{T}, A.parent)
+
+    Base.elsize(::Type{<:Adjoint{<:Real, P}}) where {P<:AbstractVecOrMat} = Base.elsize(P)
+    Base.elsize(::Type{<:Transpose{<:Any, P}}) where {P<:AbstractVecOrMat} = Base.elsize(P)
+
+end
+
 # https://github.com/JuliaLang/julia/pull/27516
 if VERSION < v"1.2.0-DEV.77"
     import Test: @inferred

test/runtests.jl

@@ -455,6 +455,33 @@ end
     @test union(Base.OneTo(3), Base.OneTo(4)) === Base.OneTo(4)
 end
 
+# https://github.com/JuliaLang/julia/pull/35929
+# https://github.com/JuliaLang/julia/pull/29135
+@testset "strided transposes" begin
+    for t in (Adjoint, Transpose)
+        @test strides(t(rand(3))) == (3, 1)
+        @test strides(t(rand(3,2))) == (3, 1)
+        @test strides(t(view(rand(3, 2), :))) == (6, 1)
+        @test strides(t(view(rand(3, 2), :, 1:2))) == (3, 1)
+
+         A = rand(3)
+        @test pointer(t(A)) === pointer(A)
+        B = rand(3,1)
+        @test pointer(t(B)) === pointer(B)
+    end
+    @test_throws MethodError strides(Adjoint(rand(3) .+ rand(3).*im))
+    @test_throws MethodError strides(Adjoint(rand(3, 2) .+ rand(3, 2).*im))
+    @test strides(Transpose(rand(3) .+ rand(3).*im)) == (3, 1)
+    @test strides(Transpose(rand(3, 2) .+ rand(3, 2).*im)) == (3, 1)
+
+     C = rand(3) .+ rand(3).*im
+    @test_throws ErrorException pointer(Adjoint(C))
+    @test pointer(Transpose(C)) === pointer(C)
+    D = rand(3,2) .+ rand(3,2).*im
+    @test_throws ErrorException pointer(Adjoint(D))
+    @test pointer(Transpose(D)) === pointer(D)
+end
+
 # https://github.com/JuliaLang/julia/pull/27516
 @testset "two arg @inferred" begin
     g(a) = a < 10 ? missing : 1