# Examples

## Extracting a number from input

    std::optional<std::string_view> extract_number(std::string_view s) noexcept {
          if (auto m = ctre::match<"[a-z]+([0-9]+)">(s)) {
            return m.get<1>().to_view();
        } else {
            return std::nullopt;
        }
    }

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## Extracting values from date

    struct date { std::string_view year; std::string_view month; std::string_view day; };
    std::optional<date> extract_date(std::string_view s) noexcept {
        using namespace ctre::literals;
        if (auto [whole, year, month, day] = ctre::match<"(\\d{4})/(\\d{1,2})/(\\d{1,2})">(s); whole) {
            return date{year, month, day};
        } else {
            return std::nullopt;
        }
    }

    //static_assert(extract_date("2018/08/27"sv).has_value());
    //static_assert((*extract_date("2018/08/27"sv)).year == "2018"sv);
    //static_assert((*extract_date("2018/08/27"sv)).month == "08"sv);
    //static_assert((*extract_date("2018/08/27"sv)).day == "27"sv);

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## Lexer

    enum class type {
        unknown, identifier, number
    };

    struct lex_item {
        type t;
        std::string_view c;
    };

    std::optional<lex_item> lexer(std::string_view v) noexcept {
        if (auto [m,id,num] = ctre::match<"([a-z]+)|([0-9]+)">(v); m) {
            if (id) {
                return lex_item{type::identifier, id};
            } else if (num) {
                return lex_item{type::number, num};
            }
        }
        return std::nullopt;
    }

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## Range over input

This support is preliminary and probably the API will be changed.

    auto input = "123,456,768"sv;

    for (auto match: ctre::range<"([0-9]+),?">(input)) {
          std::cout << std::string_view{match.get<0>()} << "\n";
    }