Function FindInStr

07-Error Handling/code/optional.cpp:6–11

#include <string>

std::optional<std::size_t> FindInStr(const std::string &str, auto pred)
{
    // Of course, you can add std::reference_wrapper.
    auto pos = std::ranges::find_if(str, pred);
    return pos == str.end() ? std::nullopt : std::optional{ pos - str.begin() };
}

int main()
{