Practicing C++ Templates

I want to get better at C++ templates. I can do the basics:

Code:

---

template<typename T>
T& min(T& t1, T& t2) {
  return t1 < t2 ? t1 : t2;
}

---

but I'm not great at parameter packs and <concepts>.

Does anyone know a good place to get practice? What I'd really love is something like leetcode, but focused on C++ templates instead of algorithms.

What's your overall knowledge of c++?

Very strong -- I've been using C++ professionally for over two decades. I can tell you about std::optional and string_view, explain the one-definition rule, and know what std::move actually does. I can write an overload and an override. I've crashed std::sort and I've signal-handled a segfault. I can even fake my way through an explanation of memory_order_relaxed vs. memory_order_acquire/memory_order_release vs. memory_order_seq_cst.

But I haven't had much chance to play with templates after the C++11 improvements, so I wanted to work on that.