C++20 string as non-type template argument example

Main.cc

#include <iostream>

struct String
{
    const char* str;
    constexpr String(const char* str) : str { str } {}
    constexpr operator const char*() const
    {
        return str;
    }
};

template <String string>
constexpr size_t StringLength()
{
    size_t rtn = 0;
    while (string[rtn]) ++rtn;
    return rtn;
}

int main()
{
    char str[StringLength<"Hello">()] = "Hell";
    static_assert(sizeof str == 5);

    std::cout << str << " world!\n";
}