Make adjoint/transpose for Diagonal lazy

Author: jishnub

src/diagonal.jl

@@ -906,11 +906,10 @@ end
 end
 
 conj(D::Diagonal) = Diagonal(conj(D.diag))
-transpose(D::Diagonal{<:Number}) = D
-transpose(D::Diagonal) = Diagonal(transpose.(D.diag))
-adjoint(D::Diagonal{<:Number}) = Diagonal(vec(adjoint(D.diag)))
-adjoint(D::Diagonal{<:Number,<:Base.ReshapedArray{<:Number,1,<:Adjoint}}) = Diagonal(adjoint(parent(D.diag)))
-adjoint(D::Diagonal) = Diagonal(adjoint.(D.diag))
+transpose(D::Diagonal) = Diagonal(vec(transpose(D.diag)))
+transpose(D::Diagonal{<:Any,<:Base.ReshapedArray{<:Any,1,<:TransposeAbsVec}}) = Diagonal(transpose(parent(D.diag)))
+adjoint(D::Diagonal) = Diagonal(vec(adjoint(D.diag)))
+adjoint(D::Diagonal{<:Any,<:Base.ReshapedArray{<:Any,1,<:AdjointAbsVec}}) = Diagonal(adjoint(parent(D.diag)))
 permutedims(D::Diagonal) = D
 permutedims(D::Diagonal, perm) = (Base.checkdims_perm(axes(D), axes(D), perm); D)
 

test/diagonal.jl

@@ -1515,4 +1515,15 @@ end
     @test_throws BoundsError D[LinearAlgebra.BandIndex(0,size(D,1)+1)]
 end
 
+@testset "lazy adjtrans" begin
+    D = Diagonal(fill([1 2; 3 4], 3))
+    m = [2 4; 6 8]
+    for op in (transpose, adjoint)
+        C = op(D)
+        el = op(m)
+        C[1,1] = el
+        @test D[1,1] == m
+    end
+end
+
 end # module TestDiagonal