Get first numbered capture utility function?

[Andersama]

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It looks like you've added functions for tokenizing / lexing. It might be useful to have a helper function to iterate across captures and/or to keep track of the first capture / index as part of the results.

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;
}

EG:

auto result =  ctre::starts_with<"([a-z]+)|([0-9]+)">(v);
return lex_item(ctre::first_capture(result).get_id(), ctre::first_capture(result).view());

Will likely improve on anything in a tight loop tokenizing results since it should remove a pretty significant branch.