Add view(::LazyTransposedMatElem, ...) (#1719)

src/Solve.jl

@@ -49,6 +49,20 @@ function Base.setindex!(M::LazyTransposeMatElem{T}, d::T, r::Int, c::Int) where
   return M
 end
 
+function AbstractAlgebra.view(M::LazyTransposeMatElem, r::Union{Colon, AbstractVector{Int}}, c::Union{Colon, AbstractVector{Int}})
+  return lazy_transpose(view(data(M), c, r))
+end
+
+# If one of the arguments is an Int, then the result is 1-dimensional so wrapping
+# it in a lazy_transpose does not make sense (and does not work, if we don't add
+# something like lazy_transpose(::AbstractVector))
+function AbstractAlgebra.view(M::LazyTransposeMatElem, r::Int, c::Union{Colon, AbstractVector{Int}})
+  return view(data(M), c, r)
+end
+function AbstractAlgebra.view(M::LazyTransposeMatElem, r::Union{Colon, AbstractVector{Int}}, c::Int)
+  return view(data(M), c, r)
+end
+
 AbstractAlgebra.base_ring(M::LazyTransposeMatElem) = base_ring(data(M))
 
 Base.zero(M::LazyTransposeMatElem) = lazy_transpose(zero(data(M)))

test/Solve-test.jl

@@ -184,6 +184,13 @@ end
   @test nrows(MT) == 5
   @test ncols(MT) == 3
 
+  V = @inferred view(MT, 1, 1:3)
+  @test V == [QQ(1), QQ(0), QQ(0)]
+  V = @inferred view(MT, 1:5, 1)
+  @test V == [QQ(1), QQ(2), QQ(3), QQ(4), QQ(5)]
+  V = @inferred view(MT, 3:4, 1:2)
+  @test V == QQ[3 8; 4 9]
+
   @test MT[2, 1] == QQ(2)
   MT[2, 1] = QQ(100)
   @test MT[2, 1] == QQ(100)