迭代表示为 std::basic_string_view 的正则表达式子匹配

Question

是否有使用 std (C++17) 转换 std::sub_match to std::basic_string_view (without constructing an intermediate std::basic_string and without intermediate heap allocation)? Or one abstraction level further, is there an alternative to std::regex_token_iterator for iterating regex submatches represented as std::basic_string_view instead of std::sub_match 的直接有效方法？

std::basic_string_view refers to a constant contiguous sequence of char-like objects with the first element of the sequence at position zero. This enables the usage of charconv's std::from_chars (which surprisingly is not implemented using ForwardIterators). This does not seem to be the case for std::sub_match，因为它表示为一对BidirectionalIterator。
std::basic_string_view 有一个更丰富的类似字符串的接口，在某些文件格式的特殊情况下有助于额外的上下文敏感标记化。

Answer 1

没有通用的方法来检测迭代器是否连续。我们仍然可以处理已知的连续迭代器——例如 std::string:

std::string_view as_sv(std::ssub_match m) {
    if(!m.matched) return {};
    return { &*m.first, m.second - m.first };
}

处理 sub_match 的其余命名特化留作 reader 的练习。

Iterating regex submatches represented as std::basic_string_view