What makes me a C++ "cultist"? I like the language, but I don't think it's a cult. And yes, they do implement their own wheel all the time (usually expertly) because libraries are reserved for functions that really need it: writing left pad is really easy. They also use third-party libraries all the time, too. They just generally pay attention to the source of that library. Google and Facebook also publish a lot of C++ libraries under one umbrella (abseil and folly respectively), and people often use one of them.