341.md

<details open><summary>Info</summary><p>

* **Did you know that C++26 added user-generated static_assert messages?**

  * https://wg21.link/P2741

</p></details><details open><summary>Example</summary><p>

```cpp
static_assert(false, std::string_view{"message"});
```

> https://godbolt.org/z/njoWdn7T7

</p></details><details open><summary>Puzzle</summary><p>

* **Can you apply format for static_assert messages?**

```cpp
// TODO format
struct foo {};
static_assert(sizeof(foo) == 0, format("Unexpected sizeof: expected 0, got {}"_s, sizeof(foo)));
```

> https://godbolt.org/z/9scM35GzP

</p></details>

</p></details><details><summary>Solutions</summary><p>

```cpp
template<auto... Cs>
constexpr auto format(const string<Cs...> fmt, auto&&... args) {
    std::array<char, sizeof...(Cs)> a{};
    for (auto i = 0; i < sizeof...(Cs); ++i) {
        if (fmt.str[i] == '{' and fmt.str[i+1] == '}') {
            a[i] = '0'+(args,...);
            a[++i] = ' ';
        } else {
            a[i] = fmt.str[i];
        }
    }
    return a;
};
```

> https://godbolt.org/z/oMd7aMqKz

</p></details>