no method matching jlopencv_core_Mat_mutable_data(::OpenCV.CxxMatDereferenced)

[timholy]

julia> img = OpenCV.Mat(rand(UInt8, 3, 32, 32));

julia> ym = OpenCV.cvtColor(img, OpenCV.COLOR_BGR2LAB);

julia> vm = OpenCV.split(ym)
ERROR: MethodError: no method matching jlopencv_core_Mat_mutable_data(::OpenCV.CxxMatDereferenced)
Closest candidates are:
  jlopencv_core_Mat_mutable_data(::Union{CxxWrap.CxxWrapCore.SmartPointer{T2}, T2} where T2<:OpenCV.CxxMatAllocated) at /home/tim/.julia/packages/CxxWrap/OcN1Z/src/CxxWrap.jl:618
Stacktrace:
 [1] cpp_to_julia(mat::OpenCV.CxxMatDereferenced)
   @ OpenCV ~/.julia/artifacts/7f7ecae944127299b78b8a360c8b5a5f94df8b2f/OpenCV/src/mat_conversion.jl:20
 [2] cpp_to_julia
   @ ~/.julia/artifacts/7f7ecae944127299b78b8a360c8b5a5f94df8b2f/OpenCV/src/mat_conversion.jl:103 [inlined]
 [3] split(m::OpenCV.Mat{UInt8}, mv::Vector{Union{OpenCV.CxxMat, AbstractArray{T, 3} where T<:Union{Float32, Float64, Int16, Int32, Int8, UInt16, UInt8}}})
   @ OpenCV ~/.julia/artifacts/7f7ecae944127299b78b8a360c8b5a5f94df8b2f/OpenCV/src/cv_cxx_wrap.jl:2305
 [4] #split#239
   @ ~/.julia/artifacts/7f7ecae944127299b78b8a360c8b5a5f94df8b2f/OpenCV/src/cv_cxx_wrap.jl:2307 [inlined]
 [5] split(m::OpenCV.Mat{UInt8})
   @ OpenCV ~/.julia/artifacts/7f7ecae944127299b78b8a360c8b5a5f94df8b2f/OpenCV/src/cv_cxx_wrap.jl:2307
 [6] top-level scope
   @ REPL[27]:1

Also noted in https://discourse.julialang.org/t/julia-opencv-binding-no-method-matching-jlopencv-core-mat-mutable-data-in-split-function/58284 (with the same split function).

[archit120]

This seems to cause many other functions to fail aswell. I am not sure how to fix this. jlopencv_core_Mat_mutable_data is defined like this and CxxMat is the Julia type for C++ Mat

    mod.method("jlopencv_core_Mat_mutable_data", [](Mat m) {
        return make_tuple(m.data, m.type(), m.channels(), m.size[1], m.size[0], m.step[1], m.step[0]);
    });

[timholy]

But it's a CxxMatDereferenced, not a CxxMat. Where does that come from?

julia> OpenCV.CxxMatDereferenced <: OpenCV.CxxMatAllocated
false

julia> OpenCV.CxxMatDereferenced <: OpenCV.CxxWrap.CxxWrapCore.SmartPointer{OpenCV.CxxMatAllocated}
false

Is this a CxxWrap issue, or something else?

[codedocpp]

I try to add a copy with x in this function (filename "mat_conversion.jl") and it successfully run, but I'm not sure if that will make the code less efficient.
function cpp_to_julia(var::CxxWrap.StdVector{T}) where {T <: CxxMat}
ret = Array{Mat, 1}()
for x in var
y=copy(x)
push!(ret, cpp_to_julia(y))
end
return ret
end