I just learned about lock_guard and I was wondering why it is a template. Until now I have only seen std::lock_guard<std::mutex> with std::mutex inside the angle brackets.

>Solution :

Using std::lock_guard<std::mutex> is indeed quite common.
But you can use std::lock_guard with other mutex types:

1. Various standard mutex types, e.g.: std::recursive_mutex.
2. Your own mutex type. You can use any type, as long as it is a BasicLockable, i.e. it supports the required methods: lock(), unlock().