2 * Copyright 2017 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) (UNLIKELY (v >= powersOf10[minLength]));
350 if (LIKELY(v < 10)) return result;
351 if (LIKELY(v < 100)) return result + 1;
352 if (LIKELY(v < 1000)) return result + 2;
353 if (LIKELY(v < 10000)) return result + 3;
354 // Skip ahead by 4 orders of magnitude
363 * Copies the ASCII base 10 representation of v into buffer and
364 * returns the number of bytes written. Does NOT append a \0. Assumes
365 * the buffer points to digits10(v) bytes of valid memory. Note that
366 * uint64 needs at most 20 bytes, uint32_t needs at most 10 bytes,
367 * uint16_t needs at most 5 bytes, and so on. Measurements suggest
368 * that defining a separate overload for 32-bit integers is not
371 * This primitive is unsafe because it makes the size assumption and
372 * because it does not add a terminating \0.
375 inline uint32_t uint64ToBufferUnsafe(uint64_t v, char *const buffer) {
376 auto const result = digits10(v);
377 // WARNING: using size_t or pointer arithmetic for pos slows down
378 // the loop below 20x. This is because several 32-bit ops can be
379 // done in parallel, but only fewer 64-bit ones.
380 uint32_t pos = result - 1;
382 // Keep these together so a peephole optimization "sees" them and
383 // computes them in one shot.
384 auto const q = v / 10;
385 auto const r = static_cast<char>(v % 10);
386 buffer[pos--] = '0' + r;
389 // Last digit is trivial to handle
390 buffer[pos] = static_cast<char>(v) + '0';
395 * A single char gets appended.
398 void toAppend(char value, Tgt * result) {
403 constexpr typename std::enable_if<
404 std::is_same<T, char>::value,
406 estimateSpaceNeeded(T) {
411 constexpr size_t estimateSpaceNeeded(const char (&)[N]) {
416 * Everything implicitly convertible to const char* gets appended.
418 template <class Tgt, class Src>
419 typename std::enable_if<
420 std::is_convertible<Src, const char*>::value
421 && IsSomeString<Tgt>::value>::type
422 toAppend(Src value, Tgt * result) {
423 // Treat null pointers like an empty string, as in:
424 // operator<<(std::ostream&, const char*).
425 const char* c = value;
427 result->append(value);
432 typename std::enable_if<std::is_convertible<Src, const char*>::value, size_t>::
434 estimateSpaceNeeded(Src value) {
435 const char *c = value;
437 return folly::StringPiece(value).size();
443 typename std::enable_if<IsSomeString<Src>::value, size_t>::type
444 estimateSpaceNeeded(Src const& value) {
449 typename std::enable_if<
450 std::is_convertible<Src, folly::StringPiece>::value &&
451 !IsSomeString<Src>::value &&
452 !std::is_convertible<Src, const char*>::value,
454 estimateSpaceNeeded(Src value) {
455 return folly::StringPiece(value).size();
459 inline size_t estimateSpaceNeeded(std::nullptr_t /* value */) {
464 typename std::enable_if<
465 std::is_pointer<Src>::value &&
466 IsSomeString<std::remove_pointer<Src>>::value,
468 estimateSpaceNeeded(Src value) {
469 return value->size();
473 * Strings get appended, too.
475 template <class Tgt, class Src>
476 typename std::enable_if<
477 IsSomeString<Src>::value && IsSomeString<Tgt>::value>::type
478 toAppend(const Src& value, Tgt * result) {
479 result->append(value);
483 * and StringPiece objects too
486 typename std::enable_if<
487 IsSomeString<Tgt>::value>::type
488 toAppend(StringPiece value, Tgt * result) {
489 result->append(value.data(), value.size());
493 * There's no implicit conversion from fbstring to other string types,
494 * so make a specialization.
497 typename std::enable_if<
498 IsSomeString<Tgt>::value>::type
499 toAppend(const fbstring& value, Tgt * result) {
500 result->append(value.data(), value.size());
503 #if FOLLY_HAVE_INT128_T
505 * Special handling for 128 bit integers.
510 toAppend(__int128 value, Tgt * result) {
511 typedef unsigned __int128 Usrc;
512 char buffer[detail::digitsEnough<unsigned __int128>() + 1];
516 p = detail::unsafeTelescope128(buffer, sizeof(buffer), -Usrc(value));
519 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
522 result->append(buffer + p, buffer + sizeof(buffer));
527 toAppend(unsigned __int128 value, Tgt * result) {
528 char buffer[detail::digitsEnough<unsigned __int128>()];
531 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
533 result->append(buffer + p, buffer + sizeof(buffer));
537 constexpr typename std::enable_if<
538 std::is_same<T, __int128>::value,
540 estimateSpaceNeeded(T) {
541 return detail::digitsEnough<__int128>();
545 constexpr typename std::enable_if<
546 std::is_same<T, unsigned __int128>::value,
548 estimateSpaceNeeded(T) {
549 return detail::digitsEnough<unsigned __int128>();
555 * int32_t and int64_t to string (by appending) go through here. The
556 * result is APPENDED to a preexisting string passed as the second
557 * parameter. This should be efficient with fbstring because fbstring
558 * incurs no dynamic allocation below 23 bytes and no number has more
559 * than 22 bytes in its textual representation (20 for digits, one for
560 * sign, one for the terminating 0).
562 template <class Tgt, class Src>
563 typename std::enable_if<
564 std::is_integral<Src>::value && std::is_signed<Src>::value &&
565 IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
566 toAppend(Src value, Tgt * result) {
569 result->push_back('-');
572 uint64ToBufferUnsafe(~static_cast<uint64_t>(value) + 1, buffer));
574 result->append(buffer, uint64ToBufferUnsafe(uint64_t(value), buffer));
579 typename std::enable_if<
580 std::is_integral<Src>::value && std::is_signed<Src>::value
581 && sizeof(Src) >= 4 && sizeof(Src) < 16,
583 estimateSpaceNeeded(Src value) {
585 // When "value" is the smallest negative, negating it would evoke
586 // undefined behavior, so, instead of writing "-value" below, we write
587 // "~static_cast<uint64_t>(value) + 1"
588 return 1 + digits10(~static_cast<uint64_t>(value) + 1);
591 return digits10(static_cast<uint64_t>(value));
595 * As above, but for uint32_t and uint64_t.
597 template <class Tgt, class Src>
598 typename std::enable_if<
599 std::is_integral<Src>::value && !std::is_signed<Src>::value
600 && IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
601 toAppend(Src value, Tgt * result) {
603 result->append(buffer, uint64ToBufferUnsafe(value, buffer));
607 typename std::enable_if<
608 std::is_integral<Src>::value && !std::is_signed<Src>::value
609 && sizeof(Src) >= 4 && sizeof(Src) < 16,
611 estimateSpaceNeeded(Src value) {
612 return digits10(value);
616 * All small signed and unsigned integers to string go through 32-bit
617 * types int32_t and uint32_t, respectively.
619 template <class Tgt, class Src>
620 typename std::enable_if<
621 std::is_integral<Src>::value
622 && IsSomeString<Tgt>::value && sizeof(Src) < 4>::type
623 toAppend(Src value, Tgt * result) {
625 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
627 toAppend<Tgt>(static_cast<Intermediate>(value), result);
631 typename std::enable_if<
632 std::is_integral<Src>::value
634 && !std::is_same<Src, char>::value,
636 estimateSpaceNeeded(Src value) {
638 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
640 return estimateSpaceNeeded(static_cast<Intermediate>(value));
644 * Enumerated values get appended as integers.
646 template <class Tgt, class Src>
647 typename std::enable_if<
648 std::is_enum<Src>::value && IsSomeString<Tgt>::value>::type
649 toAppend(Src value, Tgt * result) {
651 static_cast<typename std::underlying_type<Src>::type>(value), result);
655 typename std::enable_if<
656 std::is_enum<Src>::value, size_t>::type
657 estimateSpaceNeeded(Src value) {
658 return estimateSpaceNeeded(
659 static_cast<typename std::underlying_type<Src>::type>(value));
662 /*******************************************************************************
663 * Conversions from floating-point types to string types.
664 ******************************************************************************/
667 constexpr int kConvMaxDecimalInShortestLow = -6;
668 constexpr int kConvMaxDecimalInShortestHigh = 21;
669 } // namespace detail
671 /** Wrapper around DoubleToStringConverter **/
672 template <class Tgt, class Src>
673 typename std::enable_if<
674 std::is_floating_point<Src>::value
675 && IsSomeString<Tgt>::value>::type
679 double_conversion::DoubleToStringConverter::DtoaMode mode,
680 unsigned int numDigits) {
681 using namespace double_conversion;
682 DoubleToStringConverter
683 conv(DoubleToStringConverter::NO_FLAGS,
684 "Infinity", "NaN", 'E',
685 detail::kConvMaxDecimalInShortestLow,
686 detail::kConvMaxDecimalInShortestHigh,
687 6, // max leading padding zeros
688 1); // max trailing padding zeros
690 StringBuilder builder(buffer, sizeof(buffer));
692 case DoubleToStringConverter::SHORTEST:
693 conv.ToShortest(value, &builder);
695 case DoubleToStringConverter::FIXED:
696 conv.ToFixed(value, int(numDigits), &builder);
699 CHECK(mode == DoubleToStringConverter::PRECISION);
700 conv.ToPrecision(value, int(numDigits), &builder);
703 const size_t length = size_t(builder.position());
705 result->append(buffer, length);
709 * As above, but for floating point
711 template <class Tgt, class Src>
712 typename std::enable_if<
713 std::is_floating_point<Src>::value
714 && IsSomeString<Tgt>::value>::type
715 toAppend(Src value, Tgt * result) {
717 value, result, double_conversion::DoubleToStringConverter::SHORTEST, 0);
721 * Upper bound of the length of the output from
722 * DoubleToStringConverter::ToShortest(double, StringBuilder*),
723 * as used in toAppend(double, string*).
726 typename std::enable_if<
727 std::is_floating_point<Src>::value, size_t>::type
728 estimateSpaceNeeded(Src value) {
729 // kBase10MaximalLength is 17. We add 1 for decimal point,
730 // e.g. 10.0/9 is 17 digits and 18 characters, including the decimal point.
731 constexpr int kMaxMantissaSpace =
732 double_conversion::DoubleToStringConverter::kBase10MaximalLength + 1;
733 // strlen("E-") + digits10(numeric_limits<double>::max_exponent10)
734 constexpr int kMaxExponentSpace = 2 + 3;
735 static const int kMaxPositiveSpace = std::max({
736 // E.g. 1.1111111111111111E-100.
737 kMaxMantissaSpace + kMaxExponentSpace,
738 // E.g. 0.000001.1111111111111111, if kConvMaxDecimalInShortestLow is -6.
739 kMaxMantissaSpace - detail::kConvMaxDecimalInShortestLow,
740 // If kConvMaxDecimalInShortestHigh is 21, then 1e21 is the smallest
741 // number > 1 which ToShortest outputs in exponential notation,
742 // so 21 is the longest non-exponential number > 1.
743 detail::kConvMaxDecimalInShortestHigh
747 (value < 0 ? 1 : 0)); // +1 for minus sign, if negative
751 * This can be specialized, together with adding specialization
752 * for estimateSpaceNeed for your type, so that we allocate
753 * as much as you need instead of the default
756 struct HasLengthEstimator : std::false_type {};
759 constexpr typename std::enable_if<
760 !std::is_fundamental<Src>::value
761 #if FOLLY_HAVE_INT128_T
762 // On OSX 10.10, is_fundamental<__int128> is false :-O
763 && !std::is_same<__int128, Src>::value
764 && !std::is_same<unsigned __int128, Src>::value
766 && !IsSomeString<Src>::value
767 && !std::is_convertible<Src, const char*>::value
768 && !std::is_convertible<Src, StringPiece>::value
769 && !std::is_enum<Src>::value
770 && !HasLengthEstimator<Src>::value,
772 estimateSpaceNeeded(const Src&) {
773 return sizeof(Src) + 1; // dumbest best effort ever?
779 typename std::enable_if<IsSomeString<Tgt>::value, size_t>::type
780 estimateSpaceToReserve(size_t sofar, Tgt*) {
784 template <class T, class... Ts>
785 size_t estimateSpaceToReserve(size_t sofar, const T& v, const Ts&... vs) {
786 return estimateSpaceToReserve(sofar + estimateSpaceNeeded(v), vs...);
789 template <class... Ts>
790 void reserveInTarget(const Ts&...vs) {
791 getLastElement(vs...)->reserve(estimateSpaceToReserve(0, vs...));
794 template <class Delimiter, class... Ts>
795 void reserveInTargetDelim(const Delimiter& d, const Ts&...vs) {
796 static_assert(sizeof...(vs) >= 2, "Needs at least 2 args");
797 size_t fordelim = (sizeof...(vs) - 2) *
798 estimateSpaceToReserve(0, d, static_cast<std::string*>(nullptr));
799 getLastElement(vs...)->reserve(estimateSpaceToReserve(fordelim, vs...));
803 * Variadic base case: append one element
805 template <class T, class Tgt>
806 typename std::enable_if<
807 IsSomeString<typename std::remove_pointer<Tgt>::type>
809 toAppendStrImpl(const T& v, Tgt result) {
813 template <class T, class... Ts>
814 typename std::enable_if<
815 sizeof...(Ts) >= 2 &&
816 IsSomeString<typename std::remove_pointer<
817 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
818 toAppendStrImpl(const T& v, const Ts&... vs) {
819 toAppend(v, getLastElement(vs...));
820 toAppendStrImpl(vs...);
823 template <class Delimiter, class T, class Tgt>
824 typename std::enable_if<
825 IsSomeString<typename std::remove_pointer<Tgt>::type>::value>::type
826 toAppendDelimStrImpl(const Delimiter& /* delim */, const T& v, Tgt result) {
830 template <class Delimiter, class T, class... Ts>
831 typename std::enable_if<
832 sizeof...(Ts) >= 2 &&
833 IsSomeString<typename std::remove_pointer<
834 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
835 toAppendDelimStrImpl(const Delimiter& delim, const T& v, const Ts&... vs) {
836 // we are really careful here, calling toAppend with just one element does
837 // not try to estimate space needed (as we already did that). If we call
838 // toAppend(v, delim, ....) we would do unnecesary size calculation
839 toAppend(v, detail::getLastElement(vs...));
840 toAppend(delim, detail::getLastElement(vs...));
841 toAppendDelimStrImpl(delim, vs...);
843 } // namespace detail
846 * Variadic conversion to string. Appends each element in turn.
847 * If we have two or more things to append, we it will not reserve
848 * the space for them and will depend on strings exponential growth.
849 * If you just append once consider using toAppendFit which reserves
850 * the space needed (but does not have exponential as a result).
852 * Custom implementations of toAppend() can be provided in the same namespace as
853 * the type to customize printing. estimateSpaceNeed() may also be provided to
854 * avoid reallocations in toAppendFit():
856 * namespace other_namespace {
858 * template <class String>
859 * void toAppend(const OtherType&, String* out);
862 * size_t estimateSpaceNeeded(const OtherType&);
866 template <class... Ts>
867 typename std::enable_if<
868 sizeof...(Ts) >= 3 &&
869 IsSomeString<typename std::remove_pointer<
870 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
871 toAppend(const Ts&... vs) {
872 ::folly::detail::toAppendStrImpl(vs...);
876 // Special case pid_t on MSVC, because it's a void* rather than an
877 // integral type. We can't do a global special case because this is already
878 // dangerous enough (as most pointers will implicitly convert to a void*)
879 // just doing it for MSVC.
881 void toAppend(const pid_t a, Tgt* res) {
882 toAppend(uint64_t(a), res);
887 * Special version of the call that preallocates exaclty as much memory
888 * as need for arguments to be stored in target. This means we are
889 * not doing exponential growth when we append. If you are using it
890 * in a loop you are aiming at your foot with a big perf-destroying
892 * On the other hand if you are appending to a string once, this
893 * will probably save a few calls to malloc.
895 template <class... Ts>
896 typename std::enable_if<IsSomeString<typename std::remove_pointer<
897 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
898 toAppendFit(const Ts&... vs) {
899 ::folly::detail::reserveInTarget(vs...);
904 void toAppendFit(const Ts&) {}
907 * Variadic base case: do nothing.
910 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppend(
911 Tgt* /* result */) {}
914 * Variadic base case: do nothing.
916 template <class Delimiter, class Tgt>
917 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
918 const Delimiter& /* delim */, Tgt* /* result */) {}
921 * 1 element: same as toAppend.
923 template <class Delimiter, class T, class Tgt>
924 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
925 const Delimiter& /* delim */, const T& v, Tgt* tgt) {
930 * Append to string with a delimiter in between elements. Check out
931 * comments for toAppend for details about memory allocation.
933 template <class Delimiter, class... Ts>
934 typename std::enable_if<
935 sizeof...(Ts) >= 3 &&
936 IsSomeString<typename std::remove_pointer<
937 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
938 toAppendDelim(const Delimiter& delim, const Ts&... vs) {
939 detail::toAppendDelimStrImpl(delim, vs...);
943 * Detail in comment for toAppendFit
945 template <class Delimiter, class... Ts>
946 typename std::enable_if<IsSomeString<typename std::remove_pointer<
947 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
948 toAppendDelimFit(const Delimiter& delim, const Ts&... vs) {
949 detail::reserveInTargetDelim(delim, vs...);
950 toAppendDelim(delim, vs...);
953 template <class De, class Ts>
954 void toAppendDelimFit(const De&, const Ts&) {}
957 * to<SomeString>(v1, v2, ...) uses toAppend() (see below) as back-end
960 template <class Tgt, class... Ts>
961 typename std::enable_if<
962 IsSomeString<Tgt>::value &&
963 (sizeof...(Ts) != 1 ||
964 !std::is_same<Tgt, typename detail::LastElement<const Ts&...>::type>::
967 to(const Ts&... vs) {
969 toAppendFit(vs..., &result);
974 * Special version of to<SomeString> for floating point. When calling
975 * folly::to<SomeString>(double), generic implementation above will
976 * firstly reserve 24 (or 25 when negative value) bytes. This will
977 * introduce a malloc call for most mainstream string implementations.
979 * But for most cases, a floating point doesn't need 24 (or 25) bytes to
980 * be converted as a string.
982 * This special version will not do string reserve.
984 template <class Tgt, class Src>
985 typename std::enable_if<
986 IsSomeString<Tgt>::value && std::is_floating_point<Src>::value,
990 toAppend(value, &result);
995 * toDelim<SomeString>(SomeString str) returns itself.
997 template <class Tgt, class Delim, class Src>
998 typename std::enable_if<
999 IsSomeString<Tgt>::value &&
1000 std::is_same<Tgt, typename std::decay<Src>::type>::value,
1002 toDelim(const Delim& /* delim */, Src&& value) {
1003 return std::forward<Src>(value);
1007 * toDelim<SomeString>(delim, v1, v2, ...) uses toAppendDelim() as
1008 * back-end for all types.
1010 template <class Tgt, class Delim, class... Ts>
1011 typename std::enable_if<
1012 IsSomeString<Tgt>::value &&
1013 (sizeof...(Ts) != 1 ||
1014 !std::is_same<Tgt, typename detail::LastElement<const Ts&...>::type>::
1017 toDelim(const Delim& delim, const Ts&... vs) {
1019 toAppendDelimFit(delim, vs..., &result);
1023 /*******************************************************************************
1024 * Conversions from string types to integral types.
1025 ******************************************************************************/
1029 Expected<bool, ConversionCode> str_to_bool(StringPiece* src) noexcept;
1031 template <typename T>
1032 Expected<T, ConversionCode> str_to_floating(StringPiece* src) noexcept;
1034 extern template Expected<float, ConversionCode> str_to_floating<float>(
1035 StringPiece* src) noexcept;
1036 extern template Expected<double, ConversionCode> str_to_floating<double>(
1037 StringPiece* src) noexcept;
1039 template <class Tgt>
1040 Expected<Tgt, ConversionCode> digits_to(const char* b, const char* e) noexcept;
1042 extern template Expected<char, ConversionCode> digits_to<char>(
1044 const char*) noexcept;
1045 extern template Expected<signed char, ConversionCode> digits_to<signed char>(
1047 const char*) noexcept;
1048 extern template Expected<unsigned char, ConversionCode>
1049 digits_to<unsigned char>(const char*, const char*) noexcept;
1051 extern template Expected<short, ConversionCode> digits_to<short>(
1053 const char*) noexcept;
1054 extern template Expected<unsigned short, ConversionCode>
1055 digits_to<unsigned short>(const char*, const char*) noexcept;
1057 extern template Expected<int, ConversionCode> digits_to<int>(
1059 const char*) noexcept;
1060 extern template Expected<unsigned int, ConversionCode> digits_to<unsigned int>(
1062 const char*) noexcept;
1064 extern template Expected<long, ConversionCode> digits_to<long>(
1066 const char*) noexcept;
1067 extern template Expected<unsigned long, ConversionCode>
1068 digits_to<unsigned long>(const char*, const char*) noexcept;
1070 extern template Expected<long long, ConversionCode> digits_to<long long>(
1072 const char*) noexcept;
1073 extern template Expected<unsigned long long, ConversionCode>
1074 digits_to<unsigned long long>(const char*, const char*) noexcept;
1076 #if FOLLY_HAVE_INT128_T
1077 extern template Expected<__int128, ConversionCode> digits_to<__int128>(
1079 const char*) noexcept;
1080 extern template Expected<unsigned __int128, ConversionCode>
1081 digits_to<unsigned __int128>(const char*, const char*) noexcept;
1085 Expected<T, ConversionCode> str_to_integral(StringPiece* src) noexcept;
1087 extern template Expected<char, ConversionCode> str_to_integral<char>(
1088 StringPiece* src) noexcept;
1089 extern template Expected<signed char, ConversionCode>
1090 str_to_integral<signed char>(StringPiece* src) noexcept;
1091 extern template Expected<unsigned char, ConversionCode>
1092 str_to_integral<unsigned char>(StringPiece* src) noexcept;
1094 extern template Expected<short, ConversionCode> str_to_integral<short>(
1095 StringPiece* src) noexcept;
1096 extern template Expected<unsigned short, ConversionCode>
1097 str_to_integral<unsigned short>(StringPiece* src) noexcept;
1099 extern template Expected<int, ConversionCode> str_to_integral<int>(
1100 StringPiece* src) noexcept;
1101 extern template Expected<unsigned int, ConversionCode>
1102 str_to_integral<unsigned int>(StringPiece* src) noexcept;
1104 extern template Expected<long, ConversionCode> str_to_integral<long>(
1105 StringPiece* src) noexcept;
1106 extern template Expected<unsigned long, ConversionCode>
1107 str_to_integral<unsigned long>(StringPiece* src) noexcept;
1109 extern template Expected<long long, ConversionCode> str_to_integral<long long>(
1110 StringPiece* src) noexcept;
1111 extern template Expected<unsigned long long, ConversionCode>
1112 str_to_integral<unsigned long long>(StringPiece* src) noexcept;
1114 #if FOLLY_HAVE_INT128_T
1115 extern template Expected<__int128, ConversionCode> str_to_integral<__int128>(
1116 StringPiece* src) noexcept;
1117 extern template Expected<unsigned __int128, ConversionCode>
1118 str_to_integral<unsigned __int128>(StringPiece* src) noexcept;
1121 template <typename T>
1123 enable_if<std::is_same<T, bool>::value, Expected<T, ConversionCode>>::type
1124 convertTo(StringPiece* src) noexcept {
1125 return str_to_bool(src);
1128 template <typename T>
1129 typename std::enable_if<
1130 std::is_floating_point<T>::value,
1131 Expected<T, ConversionCode>>::type
1132 convertTo(StringPiece* src) noexcept {
1133 return str_to_floating<T>(src);
1136 template <typename T>
1137 typename std::enable_if<
1138 std::is_integral<T>::value && !std::is_same<T, bool>::value,
1139 Expected<T, ConversionCode>>::type
1140 convertTo(StringPiece* src) noexcept {
1141 return str_to_integral<T>(src);
1144 } // namespace detail
1147 * String represented as a pair of pointers to char to unsigned
1148 * integrals. Assumes NO whitespace before or after.
1150 template <typename Tgt>
1151 typename std::enable_if<
1152 std::is_integral<Tgt>::value && !std::is_same<Tgt, bool>::value,
1153 Expected<Tgt, ConversionCode>>::type
1154 tryTo(const char* b, const char* e) {
1155 return detail::digits_to<Tgt>(b, e);
1158 template <typename Tgt>
1159 typename std::enable_if<
1160 std::is_integral<Tgt>::value && !std::is_same<Tgt, bool>::value,
1162 to(const char* b, const char* e) {
1163 return tryTo<Tgt>(b, e).thenOrThrow(
1164 [](Tgt res) { return res; },
1165 [=](ConversionCode code) {
1166 return makeConversionError(code, StringPiece(b, e));
1170 /*******************************************************************************
1171 * Conversions from string types to arithmetic types.
1172 ******************************************************************************/
1175 * Parsing strings to numeric types.
1177 template <typename Tgt>
1178 FOLLY_NODISCARD inline typename std::enable_if<
1179 std::is_arithmetic<Tgt>::value,
1180 Expected<StringPiece, ConversionCode>>::type
1181 parseTo(StringPiece src, Tgt& out) {
1182 return detail::convertTo<Tgt>(&src).then(
1183 [&](Tgt res) { return void(out = res), src; });
1186 /*******************************************************************************
1187 * Integral / Floating Point to integral / Floating Point
1188 ******************************************************************************/
1193 * Bool to integral/float doesn't need any special checks, and this
1194 * overload means we aren't trying to see if a bool is less than
1197 template <class Tgt>
1198 typename std::enable_if<
1199 !std::is_same<Tgt, bool>::value &&
1200 (std::is_integral<Tgt>::value || std::is_floating_point<Tgt>::value),
1201 Expected<Tgt, ConversionCode>>::type
1202 convertTo(const bool& value) noexcept {
1203 return static_cast<Tgt>(value ? 1 : 0);
1207 * Checked conversion from integral to integral. The checks are only
1208 * performed when meaningful, e.g. conversion from int to long goes
1211 template <class Tgt, class Src>
1212 typename std::enable_if<
1213 std::is_integral<Src>::value && !std::is_same<Tgt, Src>::value &&
1214 !std::is_same<Tgt, bool>::value &&
1215 std::is_integral<Tgt>::value,
1216 Expected<Tgt, ConversionCode>>::type
1217 convertTo(const Src& value) noexcept {
1219 folly::_t<std::make_unsigned<Tgt>>(std::numeric_limits<Tgt>::max()) <
1220 folly::_t<std::make_unsigned<Src>>(std::numeric_limits<Src>::max())) {
1221 if (greater_than<Tgt, std::numeric_limits<Tgt>::max()>(value)) {
1222 return makeUnexpected(ConversionCode::ARITH_POSITIVE_OVERFLOW);
1226 std::is_signed<Src>::value &&
1227 (!std::is_signed<Tgt>::value || sizeof(Src) > sizeof(Tgt))) {
1228 if (less_than<Tgt, std::numeric_limits<Tgt>::min()>(value)) {
1229 return makeUnexpected(ConversionCode::ARITH_NEGATIVE_OVERFLOW);
1232 return static_cast<Tgt>(value);
1236 * Checked conversion from floating to floating. The checks are only
1237 * performed when meaningful, e.g. conversion from float to double goes
1240 template <class Tgt, class Src>
1241 typename std::enable_if<
1242 std::is_floating_point<Tgt>::value && std::is_floating_point<Src>::value &&
1243 !std::is_same<Tgt, Src>::value,
1244 Expected<Tgt, ConversionCode>>::type
1245 convertTo(const Src& value) noexcept {
1247 std::numeric_limits<Tgt>::max() < std::numeric_limits<Src>::max()) {
1248 if (value > std::numeric_limits<Tgt>::max()) {
1249 return makeUnexpected(ConversionCode::ARITH_POSITIVE_OVERFLOW);
1251 if (value < std::numeric_limits<Tgt>::lowest()) {
1252 return makeUnexpected(ConversionCode::ARITH_NEGATIVE_OVERFLOW);
1255 return static_cast<Tgt>(value);
1259 * Check if a floating point value can safely be converted to an
1260 * integer value without triggering undefined behaviour.
1262 template <typename Tgt, typename Src>
1263 inline typename std::enable_if<
1264 std::is_floating_point<Src>::value && std::is_integral<Tgt>::value &&
1265 !std::is_same<Tgt, bool>::value,
1267 checkConversion(const Src& value) {
1268 constexpr Src tgtMaxAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::max());
1269 constexpr Src tgtMinAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::min());
1270 if (value >= tgtMaxAsSrc) {
1271 if (value > tgtMaxAsSrc) {
1274 const Src mmax = folly::nextafter(tgtMaxAsSrc, Src());
1275 if (static_cast<Tgt>(value - mmax) >
1276 std::numeric_limits<Tgt>::max() - static_cast<Tgt>(mmax)) {
1279 } else if (std::is_signed<Tgt>::value && value <= tgtMinAsSrc) {
1280 if (value < tgtMinAsSrc) {
1283 const Src mmin = folly::nextafter(tgtMinAsSrc, Src());
1284 if (static_cast<Tgt>(value - mmin) <
1285 std::numeric_limits<Tgt>::min() - static_cast<Tgt>(mmin)) {
1292 // Integers can always safely be converted to floating point values
1293 template <typename Tgt, typename Src>
1294 constexpr typename std::enable_if<
1295 std::is_integral<Src>::value && std::is_floating_point<Tgt>::value,
1297 checkConversion(const Src&) {
1301 // Also, floating point values can always be safely converted to bool
1302 // Per the standard, any floating point value that is not zero will yield true
1303 template <typename Tgt, typename Src>
1304 constexpr typename std::enable_if<
1305 std::is_floating_point<Src>::value && std::is_same<Tgt, bool>::value,
1307 checkConversion(const Src&) {
1312 * Checked conversion from integral to floating point and back. The
1313 * result must be convertible back to the source type without loss of
1314 * precision. This seems Draconian but sometimes is what's needed, and
1315 * complements existing routines nicely. For various rounding
1316 * routines, see <math>.
1318 template <typename Tgt, typename Src>
1319 typename std::enable_if<
1320 (std::is_integral<Src>::value && std::is_floating_point<Tgt>::value) ||
1321 (std::is_floating_point<Src>::value && std::is_integral<Tgt>::value),
1322 Expected<Tgt, ConversionCode>>::type
1323 convertTo(const Src& value) noexcept {
1324 if (LIKELY(checkConversion<Tgt>(value))) {
1325 Tgt result = static_cast<Tgt>(value);
1326 if (LIKELY(checkConversion<Src>(result))) {
1327 Src witness = static_cast<Src>(result);
1328 if (LIKELY(value == witness)) {
1333 return makeUnexpected(ConversionCode::ARITH_LOSS_OF_PRECISION);
1336 template <typename Tgt, typename Src>
1337 inline std::string errorValue(const Src& value) {
1338 #ifdef FOLLY_HAS_RTTI
1339 return to<std::string>("(", demangle(typeid(Tgt)), ") ", value);
1341 return to<std::string>(value);
1345 template <typename Tgt, typename Src>
1346 using IsArithToArith = std::integral_constant<
1348 !std::is_same<Tgt, Src>::value && !std::is_same<Tgt, bool>::value &&
1349 std::is_arithmetic<Src>::value &&
1350 std::is_arithmetic<Tgt>::value>;
1352 } // namespace detail
1354 template <typename Tgt, typename Src>
1355 typename std::enable_if<
1356 detail::IsArithToArith<Tgt, Src>::value,
1357 Expected<Tgt, ConversionCode>>::type
1358 tryTo(const Src& value) noexcept {
1359 return detail::convertTo<Tgt>(value);
1362 template <typename Tgt, typename Src>
1363 typename std::enable_if<detail::IsArithToArith<Tgt, Src>::value, Tgt>::type to(
1365 return tryTo<Tgt>(value).thenOrThrow(
1366 [](Tgt res) { return res; },
1367 [&](ConversionCode e) {
1368 return makeConversionError(e, detail::errorValue<Tgt>(value));
1372 /*******************************************************************************
1373 * Custom Conversions
1375 * Any type can be used with folly::to by implementing parseTo. The
1376 * implementation should be provided in the namespace of the type to facilitate
1377 * argument-dependent lookup:
1379 * namespace other_namespace {
1380 * ::folly::Expected<::folly::StringPiece, SomeErrorCode>
1381 * parseTo(::folly::StringPiece, OtherType&) noexcept;
1383 ******************************************************************************/
1385 FOLLY_NODISCARD typename std::enable_if<
1386 std::is_enum<T>::value,
1387 Expected<StringPiece, ConversionCode>>::type
1388 parseTo(StringPiece in, T& out) noexcept {
1389 typename std::underlying_type<T>::type tmp{};
1390 auto restOrError = parseTo(in, tmp);
1391 out = static_cast<T>(tmp); // Harmless if parseTo fails
1396 inline Expected<StringPiece, ConversionCode> parseTo(
1398 StringPiece& out) noexcept {
1400 return StringPiece{in.end(), in.end()};
1404 inline Expected<StringPiece, ConversionCode> parseTo(
1408 out.append(in.data(), in.size()); // TODO try/catch?
1409 return StringPiece{in.end(), in.end()};
1413 inline Expected<StringPiece, ConversionCode> parseTo(
1417 out.append(in.data(), in.size()); // TODO try/catch?
1418 return StringPiece{in.end(), in.end()};
1422 template <typename Tgt>
1423 using ParseToResult = decltype(parseTo(StringPiece{}, std::declval<Tgt&>()));
1425 struct CheckTrailingSpace {
1426 Expected<Unit, ConversionCode> operator()(StringPiece sp) const {
1427 auto e = enforceWhitespaceErr(sp);
1428 if (UNLIKELY(e != ConversionCode::SUCCESS)) {
1429 return makeUnexpected(e);
1435 template <class Error>
1438 constexpr Expected<Unit, Error> operator()(T&&) const {
1443 // Older versions of the parseTo customization point threw on error and
1444 // returned void. Handle that.
1445 template <class Tgt>
1446 inline typename std::enable_if<
1447 std::is_void<ParseToResult<Tgt>>::value,
1448 Expected<StringPiece, ConversionCode>>::type
1449 parseToWrap(StringPiece sp, Tgt& out) {
1451 return StringPiece(sp.end(), sp.end());
1454 template <class Tgt>
1455 inline typename std::enable_if<
1456 !std::is_void<ParseToResult<Tgt>>::value,
1457 ParseToResult<Tgt>>::type
1458 parseToWrap(StringPiece sp, Tgt& out) {
1459 return parseTo(sp, out);
1462 template <typename Tgt>
1463 using ParseToError = ExpectedErrorType<decltype(
1464 detail::parseToWrap(StringPiece{}, std::declval<Tgt&>()))>;
1466 } // namespace detail
1469 * String or StringPiece to target conversion. Accepts leading and trailing
1470 * whitespace, but no non-space trailing characters.
1473 template <class Tgt>
1474 inline typename std::enable_if<
1475 !std::is_same<StringPiece, Tgt>::value,
1476 Expected<Tgt, detail::ParseToError<Tgt>>>::type
1477 tryTo(StringPiece src) {
1479 using Error = detail::ParseToError<Tgt>;
1480 using Check = typename std::conditional<
1481 std::is_arithmetic<Tgt>::value,
1482 detail::CheckTrailingSpace,
1483 detail::ReturnUnit<Error>>::type;
1484 return parseTo(src, result).then(Check(), [&](Unit) {
1485 return std::move(result);
1489 template <class Tgt, class Src>
1490 inline typename std::enable_if<
1491 IsSomeString<Src>::value && !std::is_same<StringPiece, Tgt>::value,
1493 to(Src const& src) {
1494 return to<Tgt>(StringPiece(src.data(), src.size()));
1497 template <class Tgt>
1499 typename std::enable_if<!std::is_same<StringPiece, Tgt>::value, Tgt>::type
1500 to(StringPiece src) {
1502 using Error = detail::ParseToError<Tgt>;
1503 using Check = typename std::conditional<
1504 std::is_arithmetic<Tgt>::value,
1505 detail::CheckTrailingSpace,
1506 detail::ReturnUnit<Error>>::type;
1507 auto tmp = detail::parseToWrap(src, result);
1509 .thenOrThrow(Check(), [&](Error e) { throw makeConversionError(e, src); })
1511 [&](Unit) { return std::move(result); },
1512 [&](Error e) { throw makeConversionError(e, tmp.value()); });
1516 * tryTo/to that take the strings by pointer so the caller gets information
1517 * about how much of the string was consumed by the conversion. These do not
1518 * check for trailing whitepsace.
1520 template <class Tgt>
1521 Expected<Tgt, detail::ParseToError<Tgt>> tryTo(StringPiece* src) {
1523 return parseTo(*src, result).then([&, src](StringPiece sp) -> Tgt {
1525 return std::move(result);
1529 template <class Tgt>
1530 Tgt to(StringPiece* src) {
1532 using Error = detail::ParseToError<Tgt>;
1533 return parseTo(*src, result)
1535 [&, src](StringPiece sp) -> Tgt {
1537 return std::move(result);
1539 [=](Error e) { return makeConversionError(e, *src); });
1542 /*******************************************************************************
1543 * Enum to anything and back
1544 ******************************************************************************/
1546 template <class Tgt, class Src>
1547 typename std::enable_if<
1548 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value &&
1549 !std::is_convertible<Tgt, StringPiece>::value,
1550 Expected<Tgt, ConversionCode>>::type
1551 tryTo(const Src& value) {
1552 using I = typename std::underlying_type<Src>::type;
1553 return tryTo<Tgt>(static_cast<I>(value));
1556 template <class Tgt, class Src>
1557 typename std::enable_if<
1558 !std::is_convertible<Src, StringPiece>::valuea &&
1559 std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value,
1560 Expected<Tgt, ConversionCode>>::type
1561 tryTo(const Src& value) {
1562 using I = typename std::underlying_type<Tgt>::type;
1563 return tryTo<I>(value).then([](I i) { return static_cast<Tgt>(i); });
1566 template <class Tgt, class Src>
1567 typename std::enable_if<
1568 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value &&
1569 !std::is_convertible<Tgt, StringPiece>::value,
1571 to(const Src& value) {
1572 return to<Tgt>(static_cast<typename std::underlying_type<Src>::type>(value));
1575 template <class Tgt, class Src>
1576 typename std::enable_if<
1577 !std::is_convertible<Src, StringPiece>::value && std::is_enum<Tgt>::value &&
1578 !std::is_same<Src, Tgt>::value,
1580 to(const Src& value) {
1581 return static_cast<Tgt>(to<typename std::underlying_type<Tgt>::type>(value));
1584 } // namespace folly