2 * Copyright 2011-present Facebook, Inc.
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
8 * http://www.apache.org/licenses/LICENSE-2.0
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
18 * Converts anything to anything, with an emphasis on performance and
21 * @author Andrei Alexandrescu (andrei.alexandrescu@fb.com)
34 #include <type_traits>
38 #include <double-conversion/double-conversion.h> // V8 JavaScript implementation
40 #include <folly/Demangle.h>
41 #include <folly/Expected.h>
42 #include <folly/FBString.h>
43 #include <folly/Likely.h>
44 #include <folly/Range.h>
45 #include <folly/Traits.h>
46 #include <folly/Unit.h>
47 #include <folly/portability/Math.h>
51 // Keep this in sync with kErrorStrings in Conv.cpp
52 enum class ConversionCode : unsigned char {
62 STRING_TO_FLOAT_ERROR,
63 NON_WHITESPACE_AFTER_END,
64 ARITH_POSITIVE_OVERFLOW,
65 ARITH_NEGATIVE_OVERFLOW,
66 ARITH_LOSS_OF_PRECISION,
67 NUM_ERROR_CODES, // has to be the last entry
70 struct ConversionErrorBase : std::range_error {
71 using std::range_error::range_error;
74 class ConversionError : public ConversionErrorBase {
76 ConversionError(const std::string& str, ConversionCode code)
77 : ConversionErrorBase(str), code_(code) {}
79 ConversionError(const char* str, ConversionCode code)
80 : ConversionErrorBase(str), code_(code) {}
82 ConversionCode errorCode() const {
90 /*******************************************************************************
91 * Custom Error Translation
93 * Your overloaded parseTo() function can return a custom error code on failure.
94 * ::folly::to() will call makeConversionError to translate that error code into
95 * an object to throw. makeConversionError is found by argument-dependent
96 * lookup. It should have this signature:
98 * namespace other_namespace {
99 * enum YourErrorCode { BAD_ERROR, WORSE_ERROR };
101 * struct YourConversionError : ConversionErrorBase {
102 * YourConversionError(const char* what) : ConversionErrorBase(what) {}
105 * YourConversionError
106 * makeConversionError(YourErrorCode code, ::folly::StringPiece sp) {
108 * return YourConversionError(messageString);
110 ******************************************************************************/
111 ConversionError makeConversionError(ConversionCode code, StringPiece sp);
115 * Enforce that the suffix following a number is made up only of whitespace.
117 inline ConversionCode enforceWhitespaceErr(StringPiece sp) {
119 if (UNLIKELY(!std::isspace(c))) {
120 return ConversionCode::NON_WHITESPACE_AFTER_END;
123 return ConversionCode::SUCCESS;
127 * Keep this implementation around for prettyToDouble().
129 inline void enforceWhitespace(StringPiece sp) {
130 auto err = enforceWhitespaceErr(sp);
131 if (err != ConversionCode::SUCCESS) {
132 throw makeConversionError(err, sp);
135 } // namespace detail
138 * The identity conversion function.
139 * tryTo<T>(T) returns itself for all types T.
141 template <class Tgt, class Src>
142 typename std::enable_if<
143 std::is_same<Tgt, typename std::decay<Src>::type>::value,
144 Expected<Tgt, ConversionCode>>::type
146 return std::forward<Src>(value);
149 template <class Tgt, class Src>
150 typename std::enable_if<
151 std::is_same<Tgt, typename std::decay<Src>::type>::value,
154 return std::forward<Src>(value);
157 /*******************************************************************************
158 * Arithmetic to boolean
159 ******************************************************************************/
162 * Unchecked conversion from arithmetic to boolean. This is different from the
163 * other arithmetic conversions because we use the C convention of treating any
164 * non-zero value as true, instead of range checking.
166 template <class Tgt, class Src>
167 typename std::enable_if<
168 std::is_arithmetic<Src>::value && !std::is_same<Tgt, Src>::value &&
169 std::is_same<Tgt, bool>::value,
170 Expected<Tgt, ConversionCode>>::type
171 tryTo(const Src& value) {
172 return value != Src();
175 template <class Tgt, class Src>
176 typename std::enable_if<
177 std::is_arithmetic<Src>::value && !std::is_same<Tgt, Src>::value &&
178 std::is_same<Tgt, bool>::value,
180 to(const Src& value) {
181 return value != Src();
184 /*******************************************************************************
186 ******************************************************************************/
191 // MSVC can't quite figure out the LastElementImpl::call() stuff
192 // in the base implementation, so we have to use tuples instead,
193 // which result in significantly more templates being compiled,
194 // though the runtime performance is the same.
196 template <typename... Ts>
197 auto getLastElement(Ts&&... ts) -> decltype(
198 std::get<sizeof...(Ts)-1>(std::forward_as_tuple(std::forward<Ts>(ts)...))) {
199 return std::get<sizeof...(Ts)-1>(
200 std::forward_as_tuple(std::forward<Ts>(ts)...));
203 inline void getLastElement() {}
205 template <size_t size, typename... Ts>
206 struct LastElementType : std::tuple_element<size - 1, std::tuple<Ts...>> {};
209 struct LastElementType<0> {
213 template <class... Ts>
215 : std::decay<typename LastElementType<sizeof...(Ts), Ts...>::type> {};
217 template <typename... Ts>
218 struct LastElementImpl {
219 static void call(Ignored<Ts>...) {}
222 template <typename Head, typename... Ts>
223 struct LastElementImpl<Head, Ts...> {
224 template <typename Last>
225 static Last call(Ignored<Ts>..., Last&& last) {
226 return std::forward<Last>(last);
230 template <typename... Ts>
231 auto getLastElement(const Ts&... ts)
232 -> decltype(LastElementImpl<Ts...>::call(ts...)) {
233 return LastElementImpl<Ts...>::call(ts...);
236 template <class... Ts>
237 struct LastElement : std::decay<decltype(
238 LastElementImpl<Ts...>::call(std::declval<Ts>()...))> {
242 } // namespace detail
244 /*******************************************************************************
245 * Conversions from integral types to string types.
246 ******************************************************************************/
248 #if FOLLY_HAVE_INT128_T
251 template <typename IntegerType>
252 constexpr unsigned int
254 return (unsigned int)(ceil(sizeof(IntegerType) * CHAR_BIT * M_LN2 / M_LN10));
258 unsafeTelescope128(char * buffer, size_t room, unsigned __int128 x) {
259 typedef unsigned __int128 Usrc;
262 while (x >= (Usrc(1) << 64)) { // Using 128-bit division while needed
263 const auto y = x / 10;
264 const auto digit = x % 10;
266 buffer[p--] = '0' + digit;
270 uint64_t xx = x; // Moving to faster 64-bit division thereafter
273 const auto y = xx / 10ULL;
274 const auto digit = xx % 10ULL;
276 buffer[p--] = '0' + digit;
280 buffer[p] = '0' + xx;
285 } // namespace detail
289 * Returns the number of digits in the base 10 representation of an
290 * uint64_t. Useful for preallocating buffers and such. It's also used
291 * internally, see below. Measurements suggest that defining a
292 * separate overload for 32-bit integers is not worthwhile.
295 inline uint32_t digits10(uint64_t v) {
298 // For this arch we can get a little help from specialized CPU instructions
299 // which can count leading zeroes; 64 minus that is appx. log (base 2).
300 // Use that to approximate base-10 digits (log_10) and then adjust if needed.
302 // 10^i, defined for i 0 through 19.
303 // This is 20 * 8 == 160 bytes, which fits neatly into 5 cache lines
304 // (assuming a cache line size of 64).
305 alignas(64) static const uint64_t powersOf10[20] = {
325 10000000000000000000UL,
328 // "count leading zeroes" operation not valid; for 0; special case this.
333 // bits is in the ballpark of log_2(v).
334 const uint8_t leadingZeroes = __builtin_clzll(v);
335 const auto bits = 63 - leadingZeroes;
337 // approximate log_10(v) == log_10(2) * bits.
338 // Integer magic below: 77/256 is appx. 0.3010 (log_10(2)).
339 // The +1 is to make this the ceiling of the log_10 estimate.
340 const uint32_t minLength = 1 + ((bits * 77) >> 8);
342 // return that log_10 lower bound, plus adjust if input >= 10^(that bound)
343 // in case there's a small error and we misjudged length.
344 return minLength + uint32_t(v >= powersOf10[minLength]);
350 if (LIKELY(v < 10)) {
353 if (LIKELY(v < 100)) {
356 if (LIKELY(v < 1000)) {
359 if (LIKELY(v < 10000)) {
362 // Skip ahead by 4 orders of magnitude
371 * Copies the ASCII base 10 representation of v into buffer and
372 * returns the number of bytes written. Does NOT append a \0. Assumes
373 * the buffer points to digits10(v) bytes of valid memory. Note that
374 * uint64 needs at most 20 bytes, uint32_t needs at most 10 bytes,
375 * uint16_t needs at most 5 bytes, and so on. Measurements suggest
376 * that defining a separate overload for 32-bit integers is not
379 * This primitive is unsafe because it makes the size assumption and
380 * because it does not add a terminating \0.
383 inline uint32_t uint64ToBufferUnsafe(uint64_t v, char *const buffer) {
384 auto const result = digits10(v);
385 // WARNING: using size_t or pointer arithmetic for pos slows down
386 // the loop below 20x. This is because several 32-bit ops can be
387 // done in parallel, but only fewer 64-bit ones.
388 uint32_t pos = result - 1;
390 // Keep these together so a peephole optimization "sees" them and
391 // computes them in one shot.
392 auto const q = v / 10;
393 auto const r = static_cast<char>(v % 10);
394 buffer[pos--] = '0' + r;
397 // Last digit is trivial to handle
398 buffer[pos] = static_cast<char>(v) + '0';
403 * A single char gets appended.
406 void toAppend(char value, Tgt * result) {
411 constexpr typename std::enable_if<
412 std::is_same<T, char>::value,
414 estimateSpaceNeeded(T) {
419 constexpr size_t estimateSpaceNeeded(const char (&)[N]) {
424 * Everything implicitly convertible to const char* gets appended.
426 template <class Tgt, class Src>
427 typename std::enable_if<
428 std::is_convertible<Src, const char*>::value
429 && IsSomeString<Tgt>::value>::type
430 toAppend(Src value, Tgt * result) {
431 // Treat null pointers like an empty string, as in:
432 // operator<<(std::ostream&, const char*).
433 const char* c = value;
435 result->append(value);
440 typename std::enable_if<std::is_convertible<Src, const char*>::value, size_t>::
442 estimateSpaceNeeded(Src value) {
443 const char *c = value;
445 return folly::StringPiece(value).size();
451 typename std::enable_if<IsSomeString<Src>::value, size_t>::type
452 estimateSpaceNeeded(Src const& value) {
457 typename std::enable_if<
458 std::is_convertible<Src, folly::StringPiece>::value &&
459 !IsSomeString<Src>::value &&
460 !std::is_convertible<Src, const char*>::value,
462 estimateSpaceNeeded(Src value) {
463 return folly::StringPiece(value).size();
467 inline size_t estimateSpaceNeeded(std::nullptr_t /* value */) {
472 typename std::enable_if<
473 std::is_pointer<Src>::value &&
474 IsSomeString<std::remove_pointer<Src>>::value,
476 estimateSpaceNeeded(Src value) {
477 return value->size();
481 * Strings get appended, too.
483 template <class Tgt, class Src>
484 typename std::enable_if<
485 IsSomeString<Src>::value && IsSomeString<Tgt>::value>::type
486 toAppend(const Src& value, Tgt * result) {
487 result->append(value);
491 * and StringPiece objects too
494 typename std::enable_if<
495 IsSomeString<Tgt>::value>::type
496 toAppend(StringPiece value, Tgt * result) {
497 result->append(value.data(), value.size());
501 * There's no implicit conversion from fbstring to other string types,
502 * so make a specialization.
505 typename std::enable_if<
506 IsSomeString<Tgt>::value>::type
507 toAppend(const fbstring& value, Tgt * result) {
508 result->append(value.data(), value.size());
511 #if FOLLY_HAVE_INT128_T
513 * Special handling for 128 bit integers.
518 toAppend(__int128 value, Tgt * result) {
519 typedef unsigned __int128 Usrc;
520 char buffer[detail::digitsEnough<unsigned __int128>() + 1];
524 p = detail::unsafeTelescope128(buffer, sizeof(buffer), -Usrc(value));
527 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
530 result->append(buffer + p, buffer + sizeof(buffer));
535 toAppend(unsigned __int128 value, Tgt * result) {
536 char buffer[detail::digitsEnough<unsigned __int128>()];
539 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
541 result->append(buffer + p, buffer + sizeof(buffer));
545 constexpr typename std::enable_if<
546 std::is_same<T, __int128>::value,
548 estimateSpaceNeeded(T) {
549 return detail::digitsEnough<__int128>();
553 constexpr typename std::enable_if<
554 std::is_same<T, unsigned __int128>::value,
556 estimateSpaceNeeded(T) {
557 return detail::digitsEnough<unsigned __int128>();
563 * int32_t and int64_t to string (by appending) go through here. The
564 * result is APPENDED to a preexisting string passed as the second
565 * parameter. This should be efficient with fbstring because fbstring
566 * incurs no dynamic allocation below 23 bytes and no number has more
567 * than 22 bytes in its textual representation (20 for digits, one for
568 * sign, one for the terminating 0).
570 template <class Tgt, class Src>
571 typename std::enable_if<
572 std::is_integral<Src>::value && std::is_signed<Src>::value &&
573 IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
574 toAppend(Src value, Tgt * result) {
577 result->push_back('-');
580 uint64ToBufferUnsafe(~static_cast<uint64_t>(value) + 1, buffer));
582 result->append(buffer, uint64ToBufferUnsafe(uint64_t(value), buffer));
587 typename std::enable_if<
588 std::is_integral<Src>::value && std::is_signed<Src>::value
589 && sizeof(Src) >= 4 && sizeof(Src) < 16,
591 estimateSpaceNeeded(Src value) {
593 // When "value" is the smallest negative, negating it would evoke
594 // undefined behavior, so, instead of writing "-value" below, we write
595 // "~static_cast<uint64_t>(value) + 1"
596 return 1 + digits10(~static_cast<uint64_t>(value) + 1);
599 return digits10(static_cast<uint64_t>(value));
603 * As above, but for uint32_t and uint64_t.
605 template <class Tgt, class Src>
606 typename std::enable_if<
607 std::is_integral<Src>::value && !std::is_signed<Src>::value
608 && IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
609 toAppend(Src value, Tgt * result) {
611 result->append(buffer, uint64ToBufferUnsafe(value, buffer));
615 typename std::enable_if<
616 std::is_integral<Src>::value && !std::is_signed<Src>::value
617 && sizeof(Src) >= 4 && sizeof(Src) < 16,
619 estimateSpaceNeeded(Src value) {
620 return digits10(value);
624 * All small signed and unsigned integers to string go through 32-bit
625 * types int32_t and uint32_t, respectively.
627 template <class Tgt, class Src>
628 typename std::enable_if<
629 std::is_integral<Src>::value
630 && IsSomeString<Tgt>::value && sizeof(Src) < 4>::type
631 toAppend(Src value, Tgt * result) {
633 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
635 toAppend<Tgt>(static_cast<Intermediate>(value), result);
639 typename std::enable_if<
640 std::is_integral<Src>::value
642 && !std::is_same<Src, char>::value,
644 estimateSpaceNeeded(Src value) {
646 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
648 return estimateSpaceNeeded(static_cast<Intermediate>(value));
652 * Enumerated values get appended as integers.
654 template <class Tgt, class Src>
655 typename std::enable_if<
656 std::is_enum<Src>::value && IsSomeString<Tgt>::value>::type
657 toAppend(Src value, Tgt * result) {
659 static_cast<typename std::underlying_type<Src>::type>(value), result);
663 typename std::enable_if<
664 std::is_enum<Src>::value, size_t>::type
665 estimateSpaceNeeded(Src value) {
666 return estimateSpaceNeeded(
667 static_cast<typename std::underlying_type<Src>::type>(value));
670 /*******************************************************************************
671 * Conversions from floating-point types to string types.
672 ******************************************************************************/
675 constexpr int kConvMaxDecimalInShortestLow = -6;
676 constexpr int kConvMaxDecimalInShortestHigh = 21;
677 } // namespace detail
679 /** Wrapper around DoubleToStringConverter **/
680 template <class Tgt, class Src>
681 typename std::enable_if<
682 std::is_floating_point<Src>::value
683 && IsSomeString<Tgt>::value>::type
687 double_conversion::DoubleToStringConverter::DtoaMode mode,
688 unsigned int numDigits) {
689 using namespace double_conversion;
690 DoubleToStringConverter
691 conv(DoubleToStringConverter::NO_FLAGS,
692 "Infinity", "NaN", 'E',
693 detail::kConvMaxDecimalInShortestLow,
694 detail::kConvMaxDecimalInShortestHigh,
695 6, // max leading padding zeros
696 1); // max trailing padding zeros
698 StringBuilder builder(buffer, sizeof(buffer));
700 case DoubleToStringConverter::SHORTEST:
701 conv.ToShortest(value, &builder);
703 case DoubleToStringConverter::FIXED:
704 conv.ToFixed(value, int(numDigits), &builder);
707 CHECK(mode == DoubleToStringConverter::PRECISION);
708 conv.ToPrecision(value, int(numDigits), &builder);
711 const size_t length = size_t(builder.position());
713 result->append(buffer, length);
717 * As above, but for floating point
719 template <class Tgt, class Src>
720 typename std::enable_if<
721 std::is_floating_point<Src>::value
722 && IsSomeString<Tgt>::value>::type
723 toAppend(Src value, Tgt * result) {
725 value, result, double_conversion::DoubleToStringConverter::SHORTEST, 0);
729 * Upper bound of the length of the output from
730 * DoubleToStringConverter::ToShortest(double, StringBuilder*),
731 * as used in toAppend(double, string*).
734 typename std::enable_if<
735 std::is_floating_point<Src>::value, size_t>::type
736 estimateSpaceNeeded(Src value) {
737 // kBase10MaximalLength is 17. We add 1 for decimal point,
738 // e.g. 10.0/9 is 17 digits and 18 characters, including the decimal point.
739 constexpr int kMaxMantissaSpace =
740 double_conversion::DoubleToStringConverter::kBase10MaximalLength + 1;
741 // strlen("E-") + digits10(numeric_limits<double>::max_exponent10)
742 constexpr int kMaxExponentSpace = 2 + 3;
743 static const int kMaxPositiveSpace = std::max({
744 // E.g. 1.1111111111111111E-100.
745 kMaxMantissaSpace + kMaxExponentSpace,
746 // E.g. 0.000001.1111111111111111, if kConvMaxDecimalInShortestLow is -6.
747 kMaxMantissaSpace - detail::kConvMaxDecimalInShortestLow,
748 // If kConvMaxDecimalInShortestHigh is 21, then 1e21 is the smallest
749 // number > 1 which ToShortest outputs in exponential notation,
750 // so 21 is the longest non-exponential number > 1.
751 detail::kConvMaxDecimalInShortestHigh
755 (value < 0 ? 1 : 0)); // +1 for minus sign, if negative
759 * This can be specialized, together with adding specialization
760 * for estimateSpaceNeed for your type, so that we allocate
761 * as much as you need instead of the default
764 struct HasLengthEstimator : std::false_type {};
767 constexpr typename std::enable_if<
768 !std::is_fundamental<Src>::value
769 #if FOLLY_HAVE_INT128_T
770 // On OSX 10.10, is_fundamental<__int128> is false :-O
771 && !std::is_same<__int128, Src>::value
772 && !std::is_same<unsigned __int128, Src>::value
774 && !IsSomeString<Src>::value
775 && !std::is_convertible<Src, const char*>::value
776 && !std::is_convertible<Src, StringPiece>::value
777 && !std::is_enum<Src>::value
778 && !HasLengthEstimator<Src>::value,
780 estimateSpaceNeeded(const Src&) {
781 return sizeof(Src) + 1; // dumbest best effort ever?
787 typename std::enable_if<IsSomeString<Tgt>::value, size_t>::type
788 estimateSpaceToReserve(size_t sofar, Tgt*) {
792 template <class T, class... Ts>
793 size_t estimateSpaceToReserve(size_t sofar, const T& v, const Ts&... vs) {
794 return estimateSpaceToReserve(sofar + estimateSpaceNeeded(v), vs...);
797 template <class... Ts>
798 void reserveInTarget(const Ts&...vs) {
799 getLastElement(vs...)->reserve(estimateSpaceToReserve(0, vs...));
802 template <class Delimiter, class... Ts>
803 void reserveInTargetDelim(const Delimiter& d, const Ts&...vs) {
804 static_assert(sizeof...(vs) >= 2, "Needs at least 2 args");
805 size_t fordelim = (sizeof...(vs) - 2) *
806 estimateSpaceToReserve(0, d, static_cast<std::string*>(nullptr));
807 getLastElement(vs...)->reserve(estimateSpaceToReserve(fordelim, vs...));
811 * Variadic base case: append one element
813 template <class T, class Tgt>
814 typename std::enable_if<
815 IsSomeString<typename std::remove_pointer<Tgt>::type>
817 toAppendStrImpl(const T& v, Tgt result) {
821 template <class T, class... Ts>
822 typename std::enable_if<
823 sizeof...(Ts) >= 2 &&
824 IsSomeString<typename std::remove_pointer<
825 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
826 toAppendStrImpl(const T& v, const Ts&... vs) {
827 toAppend(v, getLastElement(vs...));
828 toAppendStrImpl(vs...);
831 template <class Delimiter, class T, class Tgt>
832 typename std::enable_if<
833 IsSomeString<typename std::remove_pointer<Tgt>::type>::value>::type
834 toAppendDelimStrImpl(const Delimiter& /* delim */, const T& v, Tgt result) {
838 template <class Delimiter, class T, class... Ts>
839 typename std::enable_if<
840 sizeof...(Ts) >= 2 &&
841 IsSomeString<typename std::remove_pointer<
842 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
843 toAppendDelimStrImpl(const Delimiter& delim, const T& v, const Ts&... vs) {
844 // we are really careful here, calling toAppend with just one element does
845 // not try to estimate space needed (as we already did that). If we call
846 // toAppend(v, delim, ....) we would do unnecesary size calculation
847 toAppend(v, detail::getLastElement(vs...));
848 toAppend(delim, detail::getLastElement(vs...));
849 toAppendDelimStrImpl(delim, vs...);
851 } // namespace detail
854 * Variadic conversion to string. Appends each element in turn.
855 * If we have two or more things to append, we it will not reserve
856 * the space for them and will depend on strings exponential growth.
857 * If you just append once consider using toAppendFit which reserves
858 * the space needed (but does not have exponential as a result).
860 * Custom implementations of toAppend() can be provided in the same namespace as
861 * the type to customize printing. estimateSpaceNeed() may also be provided to
862 * avoid reallocations in toAppendFit():
864 * namespace other_namespace {
866 * template <class String>
867 * void toAppend(const OtherType&, String* out);
870 * size_t estimateSpaceNeeded(const OtherType&);
874 template <class... Ts>
875 typename std::enable_if<
876 sizeof...(Ts) >= 3 &&
877 IsSomeString<typename std::remove_pointer<
878 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
879 toAppend(const Ts&... vs) {
880 ::folly::detail::toAppendStrImpl(vs...);
884 // Special case pid_t on MSVC, because it's a void* rather than an
885 // integral type. We can't do a global special case because this is already
886 // dangerous enough (as most pointers will implicitly convert to a void*)
887 // just doing it for MSVC.
889 void toAppend(const pid_t a, Tgt* res) {
890 toAppend(uint64_t(a), res);
895 * Special version of the call that preallocates exaclty as much memory
896 * as need for arguments to be stored in target. This means we are
897 * not doing exponential growth when we append. If you are using it
898 * in a loop you are aiming at your foot with a big perf-destroying
900 * On the other hand if you are appending to a string once, this
901 * will probably save a few calls to malloc.
903 template <class... Ts>
904 typename std::enable_if<IsSomeString<typename std::remove_pointer<
905 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
906 toAppendFit(const Ts&... vs) {
907 ::folly::detail::reserveInTarget(vs...);
912 void toAppendFit(const Ts&) {}
915 * Variadic base case: do nothing.
918 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppend(
919 Tgt* /* result */) {}
922 * Variadic base case: do nothing.
924 template <class Delimiter, class Tgt>
925 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
926 const Delimiter& /* delim */, Tgt* /* result */) {}
929 * 1 element: same as toAppend.
931 template <class Delimiter, class T, class Tgt>
932 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
933 const Delimiter& /* delim */, const T& v, Tgt* tgt) {
938 * Append to string with a delimiter in between elements. Check out
939 * comments for toAppend for details about memory allocation.
941 template <class Delimiter, class... Ts>
942 typename std::enable_if<
943 sizeof...(Ts) >= 3 &&
944 IsSomeString<typename std::remove_pointer<
945 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
946 toAppendDelim(const Delimiter& delim, const Ts&... vs) {
947 detail::toAppendDelimStrImpl(delim, vs...);
951 * Detail in comment for toAppendFit
953 template <class Delimiter, class... Ts>
954 typename std::enable_if<IsSomeString<typename std::remove_pointer<
955 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
956 toAppendDelimFit(const Delimiter& delim, const Ts&... vs) {
957 detail::reserveInTargetDelim(delim, vs...);
958 toAppendDelim(delim, vs...);
961 template <class De, class Ts>
962 void toAppendDelimFit(const De&, const Ts&) {}
965 * to<SomeString>(v1, v2, ...) uses toAppend() (see below) as back-end
968 template <class Tgt, class... Ts>
969 typename std::enable_if<
970 IsSomeString<Tgt>::value &&
971 (sizeof...(Ts) != 1 ||
972 !std::is_same<Tgt, typename detail::LastElement<const Ts&...>::type>::
975 to(const Ts&... vs) {
977 toAppendFit(vs..., &result);
982 * Special version of to<SomeString> for floating point. When calling
983 * folly::to<SomeString>(double), generic implementation above will
984 * firstly reserve 24 (or 25 when negative value) bytes. This will
985 * introduce a malloc call for most mainstream string implementations.
987 * But for most cases, a floating point doesn't need 24 (or 25) bytes to
988 * be converted as a string.
990 * This special version will not do string reserve.
992 template <class Tgt, class Src>
993 typename std::enable_if<
994 IsSomeString<Tgt>::value && std::is_floating_point<Src>::value,
998 toAppend(value, &result);
1003 * toDelim<SomeString>(SomeString str) returns itself.
1005 template <class Tgt, class Delim, class Src>
1006 typename std::enable_if<
1007 IsSomeString<Tgt>::value &&
1008 std::is_same<Tgt, typename std::decay<Src>::type>::value,
1010 toDelim(const Delim& /* delim */, Src&& value) {
1011 return std::forward<Src>(value);
1015 * toDelim<SomeString>(delim, v1, v2, ...) uses toAppendDelim() as
1016 * back-end for all types.
1018 template <class Tgt, class Delim, class... Ts>
1019 typename std::enable_if<
1020 IsSomeString<Tgt>::value &&
1021 (sizeof...(Ts) != 1 ||
1022 !std::is_same<Tgt, typename detail::LastElement<const Ts&...>::type>::
1025 toDelim(const Delim& delim, const Ts&... vs) {
1027 toAppendDelimFit(delim, vs..., &result);
1031 /*******************************************************************************
1032 * Conversions from string types to integral types.
1033 ******************************************************************************/
1037 Expected<bool, ConversionCode> str_to_bool(StringPiece* src) noexcept;
1039 template <typename T>
1040 Expected<T, ConversionCode> str_to_floating(StringPiece* src) noexcept;
1042 extern template Expected<float, ConversionCode> str_to_floating<float>(
1043 StringPiece* src) noexcept;
1044 extern template Expected<double, ConversionCode> str_to_floating<double>(
1045 StringPiece* src) noexcept;
1047 template <class Tgt>
1048 Expected<Tgt, ConversionCode> digits_to(const char* b, const char* e) noexcept;
1050 extern template Expected<char, ConversionCode> digits_to<char>(
1052 const char*) noexcept;
1053 extern template Expected<signed char, ConversionCode> digits_to<signed char>(
1055 const char*) noexcept;
1056 extern template Expected<unsigned char, ConversionCode>
1057 digits_to<unsigned char>(const char*, const char*) noexcept;
1059 extern template Expected<short, ConversionCode> digits_to<short>(
1061 const char*) noexcept;
1062 extern template Expected<unsigned short, ConversionCode>
1063 digits_to<unsigned short>(const char*, const char*) noexcept;
1065 extern template Expected<int, ConversionCode> digits_to<int>(
1067 const char*) noexcept;
1068 extern template Expected<unsigned int, ConversionCode> digits_to<unsigned int>(
1070 const char*) noexcept;
1072 extern template Expected<long, ConversionCode> digits_to<long>(
1074 const char*) noexcept;
1075 extern template Expected<unsigned long, ConversionCode>
1076 digits_to<unsigned long>(const char*, const char*) noexcept;
1078 extern template Expected<long long, ConversionCode> digits_to<long long>(
1080 const char*) noexcept;
1081 extern template Expected<unsigned long long, ConversionCode>
1082 digits_to<unsigned long long>(const char*, const char*) noexcept;
1084 #if FOLLY_HAVE_INT128_T
1085 extern template Expected<__int128, ConversionCode> digits_to<__int128>(
1087 const char*) noexcept;
1088 extern template Expected<unsigned __int128, ConversionCode>
1089 digits_to<unsigned __int128>(const char*, const char*) noexcept;
1093 Expected<T, ConversionCode> str_to_integral(StringPiece* src) noexcept;
1095 extern template Expected<char, ConversionCode> str_to_integral<char>(
1096 StringPiece* src) noexcept;
1097 extern template Expected<signed char, ConversionCode>
1098 str_to_integral<signed char>(StringPiece* src) noexcept;
1099 extern template Expected<unsigned char, ConversionCode>
1100 str_to_integral<unsigned char>(StringPiece* src) noexcept;
1102 extern template Expected<short, ConversionCode> str_to_integral<short>(
1103 StringPiece* src) noexcept;
1104 extern template Expected<unsigned short, ConversionCode>
1105 str_to_integral<unsigned short>(StringPiece* src) noexcept;
1107 extern template Expected<int, ConversionCode> str_to_integral<int>(
1108 StringPiece* src) noexcept;
1109 extern template Expected<unsigned int, ConversionCode>
1110 str_to_integral<unsigned int>(StringPiece* src) noexcept;
1112 extern template Expected<long, ConversionCode> str_to_integral<long>(
1113 StringPiece* src) noexcept;
1114 extern template Expected<unsigned long, ConversionCode>
1115 str_to_integral<unsigned long>(StringPiece* src) noexcept;
1117 extern template Expected<long long, ConversionCode> str_to_integral<long long>(
1118 StringPiece* src) noexcept;
1119 extern template Expected<unsigned long long, ConversionCode>
1120 str_to_integral<unsigned long long>(StringPiece* src) noexcept;
1122 #if FOLLY_HAVE_INT128_T
1123 extern template Expected<__int128, ConversionCode> str_to_integral<__int128>(
1124 StringPiece* src) noexcept;
1125 extern template Expected<unsigned __int128, ConversionCode>
1126 str_to_integral<unsigned __int128>(StringPiece* src) noexcept;
1129 template <typename T>
1131 enable_if<std::is_same<T, bool>::value, Expected<T, ConversionCode>>::type
1132 convertTo(StringPiece* src) noexcept {
1133 return str_to_bool(src);
1136 template <typename T>
1137 typename std::enable_if<
1138 std::is_floating_point<T>::value,
1139 Expected<T, ConversionCode>>::type
1140 convertTo(StringPiece* src) noexcept {
1141 return str_to_floating<T>(src);
1144 template <typename T>
1145 typename std::enable_if<
1146 std::is_integral<T>::value && !std::is_same<T, bool>::value,
1147 Expected<T, ConversionCode>>::type
1148 convertTo(StringPiece* src) noexcept {
1149 return str_to_integral<T>(src);
1152 } // namespace detail
1155 * String represented as a pair of pointers to char to unsigned
1156 * integrals. Assumes NO whitespace before or after.
1158 template <typename Tgt>
1159 typename std::enable_if<
1160 std::is_integral<Tgt>::value && !std::is_same<Tgt, bool>::value,
1161 Expected<Tgt, ConversionCode>>::type
1162 tryTo(const char* b, const char* e) {
1163 return detail::digits_to<Tgt>(b, e);
1166 template <typename Tgt>
1167 typename std::enable_if<
1168 std::is_integral<Tgt>::value && !std::is_same<Tgt, bool>::value,
1170 to(const char* b, const char* e) {
1171 return tryTo<Tgt>(b, e).thenOrThrow(
1172 [](Tgt res) { return res; },
1173 [=](ConversionCode code) {
1174 return makeConversionError(code, StringPiece(b, e));
1178 /*******************************************************************************
1179 * Conversions from string types to arithmetic types.
1180 ******************************************************************************/
1183 * Parsing strings to numeric types.
1185 template <typename Tgt>
1186 FOLLY_NODISCARD inline typename std::enable_if<
1187 std::is_arithmetic<Tgt>::value,
1188 Expected<StringPiece, ConversionCode>>::type
1189 parseTo(StringPiece src, Tgt& out) {
1190 return detail::convertTo<Tgt>(&src).then(
1191 [&](Tgt res) { return void(out = res), src; });
1194 /*******************************************************************************
1195 * Integral / Floating Point to integral / Floating Point
1196 ******************************************************************************/
1201 * Bool to integral/float doesn't need any special checks, and this
1202 * overload means we aren't trying to see if a bool is less than
1205 template <class Tgt>
1206 typename std::enable_if<
1207 !std::is_same<Tgt, bool>::value &&
1208 (std::is_integral<Tgt>::value || std::is_floating_point<Tgt>::value),
1209 Expected<Tgt, ConversionCode>>::type
1210 convertTo(const bool& value) noexcept {
1211 return static_cast<Tgt>(value ? 1 : 0);
1215 * Checked conversion from integral to integral. The checks are only
1216 * performed when meaningful, e.g. conversion from int to long goes
1219 template <class Tgt, class Src>
1220 typename std::enable_if<
1221 std::is_integral<Src>::value && !std::is_same<Tgt, Src>::value &&
1222 !std::is_same<Tgt, bool>::value &&
1223 std::is_integral<Tgt>::value,
1224 Expected<Tgt, ConversionCode>>::type
1225 convertTo(const Src& value) noexcept {
1227 folly::_t<std::make_unsigned<Tgt>>(std::numeric_limits<Tgt>::max()) <
1228 folly::_t<std::make_unsigned<Src>>(std::numeric_limits<Src>::max())) {
1229 if (greater_than<Tgt, std::numeric_limits<Tgt>::max()>(value)) {
1230 return makeUnexpected(ConversionCode::ARITH_POSITIVE_OVERFLOW);
1234 std::is_signed<Src>::value &&
1235 (!std::is_signed<Tgt>::value || sizeof(Src) > sizeof(Tgt))) {
1236 if (less_than<Tgt, std::numeric_limits<Tgt>::min()>(value)) {
1237 return makeUnexpected(ConversionCode::ARITH_NEGATIVE_OVERFLOW);
1240 return static_cast<Tgt>(value);
1244 * Checked conversion from floating to floating. The checks are only
1245 * performed when meaningful, e.g. conversion from float to double goes
1248 template <class Tgt, class Src>
1249 typename std::enable_if<
1250 std::is_floating_point<Tgt>::value && std::is_floating_point<Src>::value &&
1251 !std::is_same<Tgt, Src>::value,
1252 Expected<Tgt, ConversionCode>>::type
1253 convertTo(const Src& value) noexcept {
1255 std::numeric_limits<Tgt>::max() < std::numeric_limits<Src>::max()) {
1256 if (value > std::numeric_limits<Tgt>::max()) {
1257 return makeUnexpected(ConversionCode::ARITH_POSITIVE_OVERFLOW);
1259 if (value < std::numeric_limits<Tgt>::lowest()) {
1260 return makeUnexpected(ConversionCode::ARITH_NEGATIVE_OVERFLOW);
1263 return static_cast<Tgt>(value);
1267 * Check if a floating point value can safely be converted to an
1268 * integer value without triggering undefined behaviour.
1270 template <typename Tgt, typename Src>
1271 inline typename std::enable_if<
1272 std::is_floating_point<Src>::value && std::is_integral<Tgt>::value &&
1273 !std::is_same<Tgt, bool>::value,
1275 checkConversion(const Src& value) {
1276 constexpr Src tgtMaxAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::max());
1277 constexpr Src tgtMinAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::min());
1278 if (value >= tgtMaxAsSrc) {
1279 if (value > tgtMaxAsSrc) {
1282 const Src mmax = folly::nextafter(tgtMaxAsSrc, Src());
1283 if (static_cast<Tgt>(value - mmax) >
1284 std::numeric_limits<Tgt>::max() - static_cast<Tgt>(mmax)) {
1287 } else if (std::is_signed<Tgt>::value && value <= tgtMinAsSrc) {
1288 if (value < tgtMinAsSrc) {
1291 const Src mmin = folly::nextafter(tgtMinAsSrc, Src());
1292 if (static_cast<Tgt>(value - mmin) <
1293 std::numeric_limits<Tgt>::min() - static_cast<Tgt>(mmin)) {
1300 // Integers can always safely be converted to floating point values
1301 template <typename Tgt, typename Src>
1302 constexpr typename std::enable_if<
1303 std::is_integral<Src>::value && std::is_floating_point<Tgt>::value,
1305 checkConversion(const Src&) {
1309 // Also, floating point values can always be safely converted to bool
1310 // Per the standard, any floating point value that is not zero will yield true
1311 template <typename Tgt, typename Src>
1312 constexpr typename std::enable_if<
1313 std::is_floating_point<Src>::value && std::is_same<Tgt, bool>::value,
1315 checkConversion(const Src&) {
1320 * Checked conversion from integral to floating point and back. The
1321 * result must be convertible back to the source type without loss of
1322 * precision. This seems Draconian but sometimes is what's needed, and
1323 * complements existing routines nicely. For various rounding
1324 * routines, see <math>.
1326 template <typename Tgt, typename Src>
1327 typename std::enable_if<
1328 (std::is_integral<Src>::value && std::is_floating_point<Tgt>::value) ||
1329 (std::is_floating_point<Src>::value && std::is_integral<Tgt>::value),
1330 Expected<Tgt, ConversionCode>>::type
1331 convertTo(const Src& value) noexcept {
1332 if (LIKELY(checkConversion<Tgt>(value))) {
1333 Tgt result = static_cast<Tgt>(value);
1334 if (LIKELY(checkConversion<Src>(result))) {
1335 Src witness = static_cast<Src>(result);
1336 if (LIKELY(value == witness)) {
1341 return makeUnexpected(ConversionCode::ARITH_LOSS_OF_PRECISION);
1344 template <typename Tgt, typename Src>
1345 inline std::string errorValue(const Src& value) {
1346 #ifdef FOLLY_HAS_RTTI
1347 return to<std::string>("(", demangle(typeid(Tgt)), ") ", value);
1349 return to<std::string>(value);
1353 template <typename Tgt, typename Src>
1354 using IsArithToArith = std::integral_constant<
1356 !std::is_same<Tgt, Src>::value && !std::is_same<Tgt, bool>::value &&
1357 std::is_arithmetic<Src>::value &&
1358 std::is_arithmetic<Tgt>::value>;
1360 } // namespace detail
1362 template <typename Tgt, typename Src>
1363 typename std::enable_if<
1364 detail::IsArithToArith<Tgt, Src>::value,
1365 Expected<Tgt, ConversionCode>>::type
1366 tryTo(const Src& value) noexcept {
1367 return detail::convertTo<Tgt>(value);
1370 template <typename Tgt, typename Src>
1371 typename std::enable_if<detail::IsArithToArith<Tgt, Src>::value, Tgt>::type to(
1373 return tryTo<Tgt>(value).thenOrThrow(
1374 [](Tgt res) { return res; },
1375 [&](ConversionCode e) {
1376 return makeConversionError(e, detail::errorValue<Tgt>(value));
1380 /*******************************************************************************
1381 * Custom Conversions
1383 * Any type can be used with folly::to by implementing parseTo. The
1384 * implementation should be provided in the namespace of the type to facilitate
1385 * argument-dependent lookup:
1387 * namespace other_namespace {
1388 * ::folly::Expected<::folly::StringPiece, SomeErrorCode>
1389 * parseTo(::folly::StringPiece, OtherType&) noexcept;
1391 ******************************************************************************/
1393 FOLLY_NODISCARD typename std::enable_if<
1394 std::is_enum<T>::value,
1395 Expected<StringPiece, ConversionCode>>::type
1396 parseTo(StringPiece in, T& out) noexcept {
1397 typename std::underlying_type<T>::type tmp{};
1398 auto restOrError = parseTo(in, tmp);
1399 out = static_cast<T>(tmp); // Harmless if parseTo fails
1404 inline Expected<StringPiece, ConversionCode> parseTo(
1406 StringPiece& out) noexcept {
1408 return StringPiece{in.end(), in.end()};
1412 inline Expected<StringPiece, ConversionCode> parseTo(
1416 out.append(in.data(), in.size()); // TODO try/catch?
1417 return StringPiece{in.end(), in.end()};
1421 inline Expected<StringPiece, ConversionCode> parseTo(
1425 out.append(in.data(), in.size()); // TODO try/catch?
1426 return StringPiece{in.end(), in.end()};
1430 template <typename Tgt>
1431 using ParseToResult = decltype(parseTo(StringPiece{}, std::declval<Tgt&>()));
1433 struct CheckTrailingSpace {
1434 Expected<Unit, ConversionCode> operator()(StringPiece sp) const {
1435 auto e = enforceWhitespaceErr(sp);
1436 if (UNLIKELY(e != ConversionCode::SUCCESS)) {
1437 return makeUnexpected(e);
1443 template <class Error>
1446 constexpr Expected<Unit, Error> operator()(T&&) const {
1451 // Older versions of the parseTo customization point threw on error and
1452 // returned void. Handle that.
1453 template <class Tgt>
1454 inline typename std::enable_if<
1455 std::is_void<ParseToResult<Tgt>>::value,
1456 Expected<StringPiece, ConversionCode>>::type
1457 parseToWrap(StringPiece sp, Tgt& out) {
1459 return StringPiece(sp.end(), sp.end());
1462 template <class Tgt>
1463 inline typename std::enable_if<
1464 !std::is_void<ParseToResult<Tgt>>::value,
1465 ParseToResult<Tgt>>::type
1466 parseToWrap(StringPiece sp, Tgt& out) {
1467 return parseTo(sp, out);
1470 template <typename Tgt>
1471 using ParseToError = ExpectedErrorType<decltype(
1472 detail::parseToWrap(StringPiece{}, std::declval<Tgt&>()))>;
1474 } // namespace detail
1477 * String or StringPiece to target conversion. Accepts leading and trailing
1478 * whitespace, but no non-space trailing characters.
1481 template <class Tgt>
1482 inline typename std::enable_if<
1483 !std::is_same<StringPiece, Tgt>::value,
1484 Expected<Tgt, detail::ParseToError<Tgt>>>::type
1485 tryTo(StringPiece src) {
1487 using Error = detail::ParseToError<Tgt>;
1488 using Check = typename std::conditional<
1489 std::is_arithmetic<Tgt>::value,
1490 detail::CheckTrailingSpace,
1491 detail::ReturnUnit<Error>>::type;
1492 return parseTo(src, result).then(Check(), [&](Unit) {
1493 return std::move(result);
1497 template <class Tgt, class Src>
1498 inline typename std::enable_if<
1499 IsSomeString<Src>::value && !std::is_same<StringPiece, Tgt>::value,
1501 to(Src const& src) {
1502 return to<Tgt>(StringPiece(src.data(), src.size()));
1505 template <class Tgt>
1507 typename std::enable_if<!std::is_same<StringPiece, Tgt>::value, Tgt>::type
1508 to(StringPiece src) {
1510 using Error = detail::ParseToError<Tgt>;
1511 using Check = typename std::conditional<
1512 std::is_arithmetic<Tgt>::value,
1513 detail::CheckTrailingSpace,
1514 detail::ReturnUnit<Error>>::type;
1515 auto tmp = detail::parseToWrap(src, result);
1517 .thenOrThrow(Check(), [&](Error e) { throw makeConversionError(e, src); })
1519 [&](Unit) { return std::move(result); },
1520 [&](Error e) { throw makeConversionError(e, tmp.value()); });
1524 * tryTo/to that take the strings by pointer so the caller gets information
1525 * about how much of the string was consumed by the conversion. These do not
1526 * check for trailing whitepsace.
1528 template <class Tgt>
1529 Expected<Tgt, detail::ParseToError<Tgt>> tryTo(StringPiece* src) {
1531 return parseTo(*src, result).then([&, src](StringPiece sp) -> Tgt {
1533 return std::move(result);
1537 template <class Tgt>
1538 Tgt to(StringPiece* src) {
1540 using Error = detail::ParseToError<Tgt>;
1541 return parseTo(*src, result)
1543 [&, src](StringPiece sp) -> Tgt {
1545 return std::move(result);
1547 [=](Error e) { return makeConversionError(e, *src); });
1550 /*******************************************************************************
1551 * Enum to anything and back
1552 ******************************************************************************/
1554 template <class Tgt, class Src>
1555 typename std::enable_if<
1556 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value &&
1557 !std::is_convertible<Tgt, StringPiece>::value,
1558 Expected<Tgt, ConversionCode>>::type
1559 tryTo(const Src& value) {
1560 using I = typename std::underlying_type<Src>::type;
1561 return tryTo<Tgt>(static_cast<I>(value));
1564 template <class Tgt, class Src>
1565 typename std::enable_if<
1566 !std::is_convertible<Src, StringPiece>::valuea &&
1567 std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value,
1568 Expected<Tgt, ConversionCode>>::type
1569 tryTo(const Src& value) {
1570 using I = typename std::underlying_type<Tgt>::type;
1571 return tryTo<I>(value).then([](I i) { return static_cast<Tgt>(i); });
1574 template <class Tgt, class Src>
1575 typename std::enable_if<
1576 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value &&
1577 !std::is_convertible<Tgt, StringPiece>::value,
1579 to(const Src& value) {
1580 return to<Tgt>(static_cast<typename std::underlying_type<Src>::type>(value));
1583 template <class Tgt, class Src>
1584 typename std::enable_if<
1585 !std::is_convertible<Src, StringPiece>::value && std::is_enum<Tgt>::value &&
1586 !std::is_same<Src, Tgt>::value,
1588 to(const Src& value) {
1589 return static_cast<Tgt>(to<typename std::underlying_type<Tgt>::type>(value));
1592 } // namespace folly