You are missing the point. No project uses all features of C++ at once, only a subset, and this forms a dialect. It's not that infrequent to see the dialect change when going from one team to another even in the same organization. Some use multiple inheritance and exceptions, some don't. Some swear by STL, some won't touch it with a long pole. That's why internal coding guidelines exist and that's why they are particularly detailed and thick for C++ shops.

The commenter above claimed that "modern C++ doesn't exist" because normally only a subset of the language is used. I disputed that, and I got his point clearly. No one is using all features of the language just for the sake of it. That doesn't make used C++ not modern.

> No project uses all features of C++ at once, only a subset

Many features of C++ are targeted at library authors. Even if a given project won't allow template metaprogramming, it probably uses vector, which certainly does. And for good reason.