Pros:
- it is convenient to type and read numbers this way;
- Ada, Perl, C++, Go and Rust already support that;
- can support thousands as well as lakhs and crores;

Cons:
- standard SQL does not have this support;
- PostgreSQL treat `SELECT 1_000_000` as number one with `_000_000` alias: http://sqlfiddle.com/#!17/0a28f/400
- C++ has `1'000'000` instead of `1_000_000`;

What do you think?

{
    return a == b || (isAlphaASCII(a) && alternateCaseIfAlphaASCII(a) == b);
}
template <typename F>
std::string trim(const std::string & str, F && predicate)
{
    size_t cut_front = 0;
    size_t cut_back = 0;
    size_t size = str.size();
    for (size_t i = 0; i < size; ++i)
    {
        if (predicate(str[i]))
            ++cut_front;
        else
            break;
    }
    if (cut_front == size)
        return {};
    for (auto it = str.rbegin(); it != str.rend(); ++it)
    {
        if (predicate(*it))
            ++cut_back;
        else
            break;
    }
    return str.substr(cut_front, size - cut_front - cut_back);
}
inline void trimLeft(std::string_view & str, char c = ' ')