Because it's so flexible, low-level in some parts (memory management, raw pointers) and high-level in others (template metaprogramming, lambdas). If you restri

Because it's so flexible, low-level in some parts (memory management, raw pointers) and high-level in others (template metaprogramming, lambdas). If you restrict the API to a subset of the language, you can make C++ ABI just fine. My favorite style is abstract interfaces. For the GUI example, look at WinRT. It exposes very high-level functionality, expressed in C++ as IUnknown-derived interfaces. These interfaces can be consumed or implemented by any compilers, or even other languages. Such APIs work well even for very performance-critical code like DirectX or Direct2D. But there's downside, such APIs is not the most idiomatic form of C++: no exceptions, no iterators or other template shenanigans, no RTTI, no standard collections not even strings. All that stuff needs to be replaced with some equivalents. When I only have C++ clients, I don't usually inherit from IUnknown, instead making an abstract base class with virtual destructor, and using std::unique_ptr smart pointers instead of CComPTR.