[356] - Did you know that C++20's no_unique_address can be used to …

…find unique types?

README.md

@@ -73,6 +73,7 @@
 
 > C++20
 
+* [Did you know that C++20's `no_unique_address` can be used to find unique types?](https://github.com/tip-of-the-week/cpp/blob/master/tips/356.md)
 * [Did you know that C++20 added constinit keyword?](https://github.com/tip-of-the-week/cpp/blob/master/tips/355.md)
 * [Did you know about C++20 `std::next_permutation` algorithm?](https://github.com/tip-of-the-week/cpp/blob/master/tips/338.md)
 * [Did you know that C++20 added `std::span`?](https://github.com/tip-of-the-week/cpp/blob/master/tips/333.md)

tips/355.md

@@ -24,5 +24,12 @@ extern constinit thread_local int var;
 
 </p></details>
 
+```cpp
+extern constinit thread_local int var;
+auto fn() { return var; }
+```
+
+> https://godbolt.org/z/rshcj6Tq5
+
 </p></details><details><summary>Solutions</summary><p>
 </p></details>

tips/356.md

@@ -0,0 +1,45 @@
+<details open><summary>Info</summary><p>
+
+* **Did you know that C++20's `no_unique_address` can be used to find unique types?**
+
+ * https://wg21.link/P0840
+
+</p></details><details open><summary>Example</summary><p>
+
+```cpp
+template<class> struct box{};
+
+struct unique {
+ [[no_unique_address]] box<int> _1;
+ [[no_unique_address]] box<bool> _2;
+};
+static_assert(sizeof(unique)==1);
+
+struct no_unique {
+ [[no_unique_address]] box<int> _1;
+ [[no_unique_address]] box<int> _2;
+};
+
+static_assert(sizeof(no_unique)!=1);
+```
+
+> https://godbolt.org/z/Mdsa16rWT
+
+</p></details><details open><summary>Puzzle</summary><p>
+
+* **Can you implement generic version of `is_unique` leveraging described concept?**
+
+```cpp
+template <class... Ts>
+constexpr auto is_unique = false; // TODO
+
+static_assert(is_unique<int, bool, char, double, float>);
+static_assert(not is_unique<int, bool, char, double, float, int>);
+```
+
+> https://godbolt.org/z/Exjdf4sbx
+
+</p></details>
+
+</p></details><details><summary>Solutions</summary><p>
+</p></details>