Initial implementation of optimal compile-time formatter generation
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@ -321,6 +321,140 @@ class compiled_format : private compiled_format_base<S> {
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explicit constexpr compiled_format(basic_string_view<char_type> format_str)
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: compiled_format_base<S>(format_str), format_str_(format_str) {}
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};
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#ifdef __cpp_if_constexpr
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template <typename... Args> struct type_list {};
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// Returns a reference to the argument at index N from [first, rest...].
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template <int N, typename T, typename... Args>
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const auto& get(const T& first, const Args&... rest) {
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if constexpr (sizeof...(Args) == 0)
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return first;
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else
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return get(rest...);
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}
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template <int N, typename> struct get_type_impl;
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template <int N, typename... Args> struct get_type_impl<N, type_list<Args...>> {
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using type = remove_cvref_t<decltype(get<N>(std::declval<Args>()...))>;
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};
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template <int N, typename T>
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using get_type = typename get_type_impl<N, T>::type;
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template <typename Char> struct text {
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basic_string_view<Char> data;
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template <typename OutputIt, typename... Args>
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OutputIt format(OutputIt out, const Args&...) {
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// TODO: reserve
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return copy_str<Char>(data.begin(), data.end(), out);
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}
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};
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template <typename Char>
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constexpr text<Char> make_text(basic_string_view<Char> s, size_t pos,
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size_t size) {
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return {{&s[pos], size}};
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}
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template <typename Char, typename OutputIt, typename T,
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std::enable_if_t<std::is_integral_v<T>, int> = 0>
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OutputIt format_default(OutputIt out, T value) {
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// TODO: reserve
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format_int fi(value);
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return std::copy(fi.data(), fi.data() + fi.size(), out);
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}
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template <typename Char, typename OutputIt>
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OutputIt format_default(OutputIt out, Char value) {
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*out++ = value;
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return out;
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}
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template <typename Char, typename OutputIt>
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OutputIt format_default(OutputIt out, const Char* value) {
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auto length = std::char_traits<Char>::length(value);
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return copy_str<Char>(value, value + length, out);
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}
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// A replacement field that refers to argument N.
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template <typename Char, typename T, int N> struct field {
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template <typename OutputIt, typename... Args>
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OutputIt format(OutputIt out, const Args&... args) {
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// This ensures that the argument type is convertile to `const T&`.
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const T& arg = get<N>(args...);
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return format_default<Char>(out, arg);
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}
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};
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template <typename L, typename R> struct concat {
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L lhs;
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R rhs;
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template <typename OutputIt, typename... Args>
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OutputIt format(OutputIt out, const Args&... args) {
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out = lhs.format(out, args...);
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return rhs.format(out, args...);
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}
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};
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template <typename L, typename R>
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constexpr concat<L, R> make_concat(L lhs, R rhs) {
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return {lhs, rhs};
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}
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template <typename Char>
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constexpr size_t parse_text(basic_string_view<Char> str, size_t pos) {
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for (size_t size = str.size(); pos != size; ++pos) {
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if (str[pos] == '{' || str[pos] == '}') break;
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}
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return pos;
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}
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template <typename Args, size_t POS, int ID, typename S>
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constexpr auto compile_format_string(S format_str);
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template <typename Args, size_t POS, int ID, typename T, typename S>
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auto parse_tail(T head, S format_str) {
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if constexpr (POS != to_string_view(format_str).size())
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return make_concat(head, compile_format_string<Args, POS, ID>(format_str));
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else
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return head;
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}
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template <typename Args, size_t POS, int ID, typename S>
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constexpr auto compile_format_string(S format_str) {
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using char_type = char_t<S>;
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constexpr basic_string_view<char_type> str = format_str;
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if constexpr (str.size() == 0) {
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return make_text(str, 0, 0);
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} else if constexpr (str[POS] == '{') {
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if (POS + 1 == str.size())
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throw format_error("unmatched '{' in format string");
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if constexpr (str[POS + 1] == '{') {
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return parse_tail<Args, POS + 2, ID>(make_text(str, POS, 1), format_str);
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} else if constexpr (str[POS + 1] == '}') {
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return parse_tail<Args, POS + 2, ID + 1>(
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field<char_type, get_type<ID, Args>, ID>(), format_str);
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} else {
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throw format_error("invalid format string");
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}
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} else if constexpr (str[POS] == '}') {
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if (POS + 1 == str.size())
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throw format_error("unmatched '}' in format string");
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return parse_tail<Args, POS + 2, ID>(make_text(str, POS, 1), format_str);
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} else {
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constexpr auto end = parse_text(str, POS + 1);
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return parse_tail<Args, end, ID>(make_text(str, POS, end - POS),
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format_str);
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}
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}
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template <typename... Args, typename S> constexpr auto compile(S format_str) {
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return compile_format_string<type_list<Args...>, 0, 0>(format_str);
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}
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#endif // __cpp_if_constexpr
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} // namespace internal
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#if FMT_USE_CONSTEXPR
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@ -295,6 +295,8 @@ template <typename Char> class basic_string_view {
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FMT_CONSTEXPR iterator begin() const { return data_; }
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FMT_CONSTEXPR iterator end() const { return data_ + size_; }
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FMT_CONSTEXPR const Char& operator[](size_t pos) const { return data_[pos]; }
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FMT_CONSTEXPR void remove_prefix(size_t n) {
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data_ += n;
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size_ -= n;
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