incomplete type for std::any when GMOCKing interface

问题

I have a very weird compilation problem with this snippet:

#include <any>
#include <gmock/gmock.h>


struct Class
{
    virtual std::any get(int, int) = 0;
};


struct MockClass: Class
{
    MOCK_METHOD2(get, std::any(int, int));
};


int foo()
{
    MockClass dd;
}

Error gcc 9.1.0:

/usr/include/c++/9.1.0/type_traits:131:12: error: incomplete type ‘std::is_copy_constructible<testing::internal::ReferenceOrValueWrapper<std::any> >’ used in nested name specifier

clang 8.0.0:

/usr/bin/../lib64/gcc/x86_64-pc-linux-gnu/9.1.0/../../../../include/c++/9.1.0/type_traits:132:31: error: no member named 'value' in 'std::is_copy_constructible<testing::internal::ReferenceOrValueWrapper<std::any> >'

If I replace std::any with std::string or any other common type, code compiles.

回答1:

This is libstdc++ bug 90415.

I am not sure what it is about std::any that causes this problem. Note that your example fails on clang using libstdc++, but succeeds when using libc++.

回答2:

Additional information about this issue, that I have got a workaround to use any with gmock in gcc 9.1.0, use std::experimental::fundamentals_v1::any instead of std::any, and it works fine.

来源：https://stackoverflow.com/questions/57332965/incomplete-type-for-stdany-when-gmocking-interface