Avoid copy in getindex(::AbstractQ, ...) (#44729)

JuliaLang · Mar 25, 2022 · ea82910 · ea82910
1 parent 68e2969
commit ea82910
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Showing 2 changed files with 9 additions and 2 deletions.
diff --git a/stdlib/LinearAlgebra/src/qr.jl b/stdlib/LinearAlgebra/src/qr.jl
@@ -582,8 +582,9 @@ size(F::Union{QR,QRCompactWY,QRPivoted}) = size(getfield(F, :factors))
 size(Q::AbstractQ, dim::Integer) = size(getfield(Q, :factors), dim == 2 ? 1 : dim)
 size(Q::AbstractQ) = size(Q, 1), size(Q, 2)
 
-copy(Q::AbstractQ{T}) where {T} = lmul!(Q, Matrix{T}(I, size(Q)))
-getindex(Q::AbstractQ, inds...) = copy(Q)[inds...]
+copymutable(Q::AbstractQ{T}) where {T} = lmul!(Q, Matrix{T}(I, size(Q)))
+copy(Q::AbstractQ) = copymutable(Q)
+getindex(Q::AbstractQ, inds...) = copymutable(Q)[inds...]
 getindex(Q::AbstractQ, ::Colon, ::Colon) = copy(Q)
 
 function getindex(Q::AbstractQ, ::Colon, j::Int)

diff --git a/stdlib/LinearAlgebra/test/qr.jl b/stdlib/LinearAlgebra/test/qr.jl
@@ -449,6 +449,12 @@ end
  @test Q2[:, :] ≈ M[:, :]
  @test Q2[:, :, :] ≈ M[:, :, :]
  end
+ # Check that getindex works if copy returns itself (#44729)
+ struct MyIdentity{T} <: LinearAlgebra.AbstractQ{T} end
+ Base.size(::MyIdentity, dim::Integer) = dim in (1,2) ? 2 : 1
+ Base.copy(J::MyIdentity) = J
+ LinearAlgebra.lmul!(::MyIdentity{T}, M::Array{T}) where {T} = M
+ @test MyIdentity{Float64}()[1,:] == [1.0, 0.0]
 end
 
 end # module TestQR