373 - Did you know that C++23 added constexpr bitset?

README.md

@@ -42,6 +42,7 @@
 
 > C++23
 
+* [Did you know that C++23 added constexpr `bitset`?](https://github.com/tip-of-the-week/cpp/blob/master/tips/373.md)
 * [Did you know that C++23 added Explicit lifetime management (1/N)?](https://github.com/tip-of-the-week/cpp/blob/master/tips/368.md)
 * [Did you know that C++23 added spanstream - A strstream replacement using span<charT> as buffer?](https://github.com/tip-of-the-week/cpp/blob/master/tips/360.md)
 * [Did you know that C++23 added standard support for `flat_map`?](https://github.com/tip-of-the-week/cpp/blob/master/tips/357.md)

tips/373.md

@@ -0,0 +1,54 @@
+<details open><summary>Info</summary><p>
+
+* **Did you know that C++23 added constexpr `bitset`?**
+
+  * https://wg21.link/P2417
+
+</p></details><details open><summary>Example</summary><p>
+
+```cpp
+#include <bitset>
+constexpr std::bitset<8> bs{0b00000001};
+static_assert(bs.test(0));
+static_assert(not bs.test(1));
+```
+
+> https://godbolt.org/z/W4v1Kqcfv
+
+</p></details><details open><summary>Puzzle</summary><p>
+
+* **Can you implement bitset `reverse`?**
+
+```cpp
+template<auto Size>
+constexpr auto reverse(std::bitset<Size> bs); // TODO
+
+static_assert(0b10000000 == reverse(std::bitset<8>{0b00000001}));
+static_assert(0b10000001 == reverse(std::bitset<8>{0b10000001}));
+static_assert(0b11100001 == reverse(std::bitset<8>{0b10000111}));
+```
+
+> https://godbolt.org/z/d75sW5E9x
+
+</p></details>
+
+</p></details><details><summary>Solutions</summary><p>
+
+```cpp
+template<auto Size>
+constexpr auto reverse(std::bitset<Size> bs) {
+  std::bitset<Size> r{};
+  for (auto i = 0; i < bs.size(); ++i) {
+    r[r.size()-i-1] = bs[i];
+  }
+  return r;
+}
+
+static_assert(0b10000000 == reverse(std::bitset<8>{0b00000001}));
+static_assert(0b10000001 == reverse(std::bitset<8>{0b10000001}));
+static_assert(0b11100001 == reverse(std::bitset<8>{0b10000111}));
+```
+
+> https://godbolt.org/z/8h9PGP5o6
+
+</p></details>