TheRock/compiler/amd-llvm/clang-tools-extra/docs/clang-tidy/checks/portability/template-virtual-member-function.rst

.. title:: clang-tidy - portability-template-virtual-member-function

portability-template-virtual-member-function
============================================

Finds cases when an uninstantiated virtual member function in a template class
causes cross-compiler incompatibility.

Upon instantiating a template class, non-virtual member functions don't have
to be instantiated unless they are used. Virtual member function instantiation
on the other hand is unspecified and depends on the implementation of the
compiler.

In the following snippets the virtual member function is not instantiated by
GCC and Clang, but it is instantiated by MSVC, so while the snippet is accepted
by the former compilers, it is rejected by the latter.

.. code:: c++

    template<typename T>
    struct CrossPlatformError {
        virtual ~CrossPlatformError() = default;

        static void used() {}

        virtual void unused() {
            T MSVCError = this;
        };
    };

    int main() {
        CrossPlatformError<int>::used();
        return 0;
    }

Cross-platform projects that need to support MSVC on Windows might see compiler
errors because certain virtual member functions are instantiated, which are not
instantiated by other compilers on other platforms. This check highlights such
virtual member functions.