BOOST_TEST_CHECK can't compare abstract classes using gcc

[Marc-Aldorasi-Imprivata]

struct abstract
{
    virtual ~abstract() = 0;
    bool operator==(const abstract &) const;
};

std::ostream &operator<<(std::ostream &, const abstract &);

void foo(abstract &a)
{
    BOOST_TEST_CHECK(a == a); // Fails
    BOOST_CHECK_EQUAL(a, a); // Works
}

Godbolt. When compiling this code, GCC complains that it can't instantiate the member functions of std::numeric_limits with an abstract type. Boost Test should check if numeric_limits is instantiable with a specific type before attempting to instantiate it; see https://stackoverflow.com/questions/16505782/determining-if-stdnumeric-limitst-is-safe-to-instantiate for a longer discussion of the issue and possible implementations.

[raffienficiaud]

I've made a fix, annoyingly the problem does not happen on clang/OSX. Waiting for CI checks.

[raffienficiaud]

Would it be possible for you to check the branch topic/GH-209-BOOST_TEST-abstract-class-compare. Right now it contains some failures on C++03 for comparing abstract classes (not sure I will be able to improve the support there) but otherwise seems to do the job.

[Marc-Aldorasi-Imprivata]

That branch works for me.