Force compiler to emit error on move constructor not defined with a base class deleted copy ctor

Question

Consider a base class wich prevent copy construction and copy assignement like this:

class NonCopyable {
    public:
        NonCopyable() = default;
        ~NonCopyable() = default;

        NonCopyable(NonCopyable const&)                 = delete;
        NonCopyable& operator=(NonCopyable const&)      = delete;
};

Our developers can now include this class, and use it to disable copy for inherited classes, like this:

class CopyTest : public NonCopyable {
    public:
        CopyTest() {
            std::cout << "copy test created" << std::endl;
        }

        ~CopyTest() {
            std::cout << "copy test deleted" << std::endl;
        }
};

When I try to use the CopyTest class:

CopyTest ct, ct1(ct);

or

CopyTest ct;
CopyTest ct1 = ct2;

The compiler emit an error : use of deleted function xxx (where xxx is my deleted copy ctor, or copy operator)

Then, if I want to std::move a CopyTest object :

CopyTest ct;
CopyTest ct1 = std::move(ct);

The compiler emit the same error (use of deleted function xxx - where xxx remains my copy ctor or assignement operator).

If I remind correctly, it's because the developer has not defined the proper move ctor/assignement operator.

Is it possible to force the compiler to tell the developper of the CopyTest class that the move error is here because he has not defined the proper move ctor/assignement operator, and not because the copy ctor/assignement operator is deleted on the base class?

Platform :

Debian 9

GCC 6.3.0

Compilation flags :

-fpermissive -ggdb -std=c++11

Any good developer will know that the probable cause of this error is the lack of a move constructor (He is using std::move, after all). I wouldn't worry about it. — Cássio Renan
I agree with you, but I don't want to rely on other people nor my probable skills, and thought that an exact compiler error was easier to be understood by beginners like me... — Ayak973
The compiler error is exact: the implicitly defined move constructor is deleted, because the copy ctor is. — Walter

Yakk - Adam Nevraumont Yakk - Adam Nevraumont · Accepted Answer · 2018-12-12T19:55:19

add

    NonCopyable(NonCopyable &&)                 = delete;
    NonCopyable& operator=(NonCopyable &&)      = delete;

that now complains about the base class move ctor being deleted.

Force compiler to emit error on move constructor not defined with a base class deleted copy ctor

2 Answers