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";
}