Function FindIndexIf

util/generic/algorithm.h:203–208

template <class C, class P>
constexpr size_t FindIndexIf(C&& c, P p) {
    using std::begin;
    using std::end;
    auto it = FindIf(begin(c), end(c), p);
    return it == end(c) ? NPOS : (it - begin(c));
}

// EqualToOneOf(x, "apple", "orange") means (x == "apple" || x == "orange")
template <typename T, typename... Other>