This week I learned 27

This week I learned you can evaluate the length of a constexpr string at compile-time.

#include <cstring>

constexpr std::size_t len(const char *x)
{
    return '\0' == *x ? 0 : 1 + len(++x);
}

int main()
{
    constexpr const auto a = "foobar";
    static_assert(len(a) == 6, "oh no!");
}