unique_ptr & vector, trying to access deleted function, Visual Studio 2013

Question

I am trying to use unique_ptr to manage my memory, and VS2013 seems to be giving me trouble when I think it shouldn't be.

It would seem that the compiler is for whatever reason trying to access a deleted copy constructor when it really should have no reason to do so.

This is what one of my classes looks like:

class Mesh
{
public:
    Mesh(oglplus::Program* program, const std::vector<Vertex>& vertices, 
                    const std::vector<GLuint>& indices);
    void draw();
private:
    const oglplus::Program* _program;
    std::vector<Vertex> _vertices;
    std::vector<GLuint> _indices;
    oglplus::Buffer _faceBuffer;
    oglplus::Buffer _vertexBuffer;
    oglplus::VertexArray _vao;
};

class Model
{
public:
    Model(std::string filename, oglplus::Program* program);
    void draw();
private:
    const oglplus::Program* _program;
    std::vector<std::unique_ptr<Mesh>> _meshes;
};

The issue is with the line

 std::vector<std::unique_ptr<Mesh>> _meshes;

it starts spewing things like

2>c:\program files (x86)\microsoft visual studio 12.0\vc\include\xmemory0(593): error C2280: 'std::unique_ptr<Model::Mesh,std::default_delete<_Ty>>::unique_ptr(const std::unique_ptr<_Ty,std::default_delete<_Ty>> &)' : attempting to reference a deleted function
2>          with
2>          [
2>              _Ty=Model::Mesh
2>          ]
2>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\memory(1486) : see declaration of 'std::unique_ptr<Model::Mesh,std::default_delete<_Ty>>::unique_ptr'
2>          with
2>          [
2>              _Ty=Model::Mesh
2>          ]
2>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\xmemory0(592) : while compiling class template member function 'void std::allocator<_Ty>::construct(_Ty *,const _Ty &)'
2>          with
2>          [
2>              _Ty=std::unique_ptr<Model::Mesh,std::default_delete<Model::Mesh>>
2>          ]
2>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\xmemory0(723) : see reference to function template instantiation 'void std::allocator<_Ty>::construct(_Ty *,const _Ty &)' being compiled
2>          with
2>          [
2>              _Ty=std::unique_ptr<Model::Mesh,std::default_delete<Model::Mesh>>
2>          ]
2>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\type_traits(572) : see reference to class template instantiation 'std::allocator<_Ty>' being compiled
2>          with
2>          [
2>              _Ty=std::unique_ptr<Model::Mesh,std::default_delete<Model::Mesh>>
2>          ]
2>          c:\program files (x86)\microsoft visual studio 12.0\vc\include\vector(650) : see reference to class template instantiation 'std::is_empty<_Alloc>' being compiled
2>          with
2>          [
2>              _Alloc=std::allocator<std::unique_ptr<Model::Mesh,std::default_delete<Model::Mesh>>>
2>          ]
2>          c:\users\vitali\projects\3d-stg\source\model\model.hpp(45) : see reference to class template instantiation 'std::vector<std::unique_ptr<Model::Mesh,std::default_delete<_Ty>>,std::allocator<std::unique_ptr<_Ty,std::default_delete<_Ty>>>>' being compiled
2>          with
2>          [
2>              _Ty=Model::Mesh
2>          ]
2>  model.cpp

I am not using std::vector::resize() or anything like that (in-fact I commented out all uses of my _meshes vector, and even tried commenting the implementation out completely to no avail), so I don't understand why the compiler is giving me issues.

Does anybody have any ideas?

---

Thank you Preetish Kakkar for finding the issue. It turns out it was an issue with compiler generated functions implicitly using the copy constructor and operator= of the Mesh class forcing the compiler to try and use deleted functions.

Answer 1

I reproduced your problem, below is sample code.

#include <vector>
#include <memory>

class Mesh
{
public: 
    Mesh() {}
    void draw() {}
private:
};

class Model
{
public:
    Model() {}
    void draw() {}
private:
    typedef std::unique_ptr<Mesh> MeshUniquePtr;
    std::vector<MeshUniquePtr> _meshes;
};


int _tmain(int argc, _TCHAR* argv[])
{
    Model m;
    Model m1;
    m = m1; // causes error as you can't copy unique ptr

    return 0;
}

The problem is at some point you are trying to copy two model object which can't be done as unique_ptr is not copyable.