std::ranges::starts_with

cppreference.com

Example

Run on Compiler Explorer

main: () = {
    using std::literals::_;

    ascii_upper:== :(c: char) -> char == {
        if 'a' <= c && c <= 'z' {
            return cpp2::unsafe_narrow<char>(c + 'A' - 'a');
        }
        else {
            return c;
        }
    };

    cmp_ignore_case:== :(x: char, y: char) -> bool == {
        return ascii_upper$(x) == ascii_upper$(y);
    };

    static_assert( std::ranges::starts_with("const_cast", "const"sv));
    static_assert( std::ranges::starts_with("constexpr",  "const"sv));
    static_assert(!std::ranges::starts_with("volatile",   "const"sv));

    std::cout << std::boolalpha
              << std::ranges::starts_with("Constantinopolis", "constant"sv,
                                          (), ascii_upper, ascii_upper) << ' '
              << std::ranges::starts_with("Istanbul", "constant"sv,
                                          (), ascii_upper, ascii_upper) << ' '
              << std::ranges::starts_with("Metropolis", "metro"sv,
                                          cmp_ignore_case) << ' '
              << std::ranges::starts_with("Acropolis", "metro"sv,
                                          cmp_ignore_case) << '\n';

    v: std::array == (1, 3, 5, 7, 9);
    odd:== :(x: int) -> bool == x % 2;
    static_assert(std::ranges::starts_with(v, std::views::iota(1)
                                            | std::views::filter(odd)
                                            | std::views::take(3)));
}

Output

true false true false