2 * Copyright 2016 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 <boost/implicit_cast.hpp>
39 #include <double-conversion/double-conversion.h> // V8 JavaScript implementation
41 #include <folly/Demangle.h>
42 #include <folly/Expected.h>
43 #include <folly/FBString.h>
44 #include <folly/Likely.h>
45 #include <folly/Range.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);
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;
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 static const uint64_t powersOf10[20] FOLLY_ALIGNED(64) = {
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<uint32_t>(v % 10);
386 buffer[pos--] = '0' + r;
389 // Last digit is trivial to handle
390 buffer[pos] = static_cast<uint32_t>(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 * Everything implicitly convertible to const char* gets appended.
413 template <class Tgt, class Src>
414 typename std::enable_if<
415 std::is_convertible<Src, const char*>::value
416 && IsSomeString<Tgt>::value>::type
417 toAppend(Src value, Tgt * result) {
418 // Treat null pointers like an empty string, as in:
419 // operator<<(std::ostream&, const char*).
420 const char* c = value;
422 result->append(value);
427 typename std::enable_if<std::is_convertible<Src, const char*>::value, size_t>::
429 estimateSpaceNeeded(Src value) {
430 const char *c = value;
432 return folly::StringPiece(value).size();
438 typename std::enable_if<
439 (std::is_convertible<Src, folly::StringPiece>::value ||
440 IsSomeString<Src>::value) &&
441 !std::is_convertible<Src, const char*>::value,
443 estimateSpaceNeeded(Src value) {
444 return folly::StringPiece(value).size();
448 inline size_t estimateSpaceNeeded(std::nullptr_t /* value */) {
453 typename std::enable_if<
454 std::is_pointer<Src>::value &&
455 IsSomeString<std::remove_pointer<Src>>::value,
457 estimateSpaceNeeded(Src value) {
458 return value->size();
462 * Strings get appended, too.
464 template <class Tgt, class Src>
465 typename std::enable_if<
466 IsSomeString<Src>::value && IsSomeString<Tgt>::value>::type
467 toAppend(const Src& value, Tgt * result) {
468 result->append(value);
472 * and StringPiece objects too
475 typename std::enable_if<
476 IsSomeString<Tgt>::value>::type
477 toAppend(StringPiece value, Tgt * result) {
478 result->append(value.data(), value.size());
482 * There's no implicit conversion from fbstring to other string types,
483 * so make a specialization.
486 typename std::enable_if<
487 IsSomeString<Tgt>::value>::type
488 toAppend(const fbstring& value, Tgt * result) {
489 result->append(value.data(), value.size());
492 #if FOLLY_HAVE_INT128_T
494 * Special handling for 128 bit integers.
499 toAppend(__int128 value, Tgt * result) {
500 typedef unsigned __int128 Usrc;
501 char buffer[detail::digitsEnough<unsigned __int128>() + 1];
505 p = detail::unsafeTelescope128(buffer, sizeof(buffer), -Usrc(value));
508 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
511 result->append(buffer + p, buffer + sizeof(buffer));
516 toAppend(unsigned __int128 value, Tgt * result) {
517 char buffer[detail::digitsEnough<unsigned __int128>()];
520 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
522 result->append(buffer + p, buffer + sizeof(buffer));
526 constexpr typename std::enable_if<
527 std::is_same<T, __int128>::value,
529 estimateSpaceNeeded(T) {
530 return detail::digitsEnough<__int128>();
534 constexpr typename std::enable_if<
535 std::is_same<T, unsigned __int128>::value,
537 estimateSpaceNeeded(T) {
538 return detail::digitsEnough<unsigned __int128>();
544 * int32_t and int64_t to string (by appending) go through here. The
545 * result is APPENDED to a preexisting string passed as the second
546 * parameter. This should be efficient with fbstring because fbstring
547 * incurs no dynamic allocation below 23 bytes and no number has more
548 * than 22 bytes in its textual representation (20 for digits, one for
549 * sign, one for the terminating 0).
551 template <class Tgt, class Src>
552 typename std::enable_if<
553 std::is_integral<Src>::value && std::is_signed<Src>::value &&
554 IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
555 toAppend(Src value, Tgt * result) {
558 result->push_back('-');
559 result->append(buffer, uint64ToBufferUnsafe(-uint64_t(value), buffer));
561 result->append(buffer, uint64ToBufferUnsafe(value, buffer));
566 typename std::enable_if<
567 std::is_integral<Src>::value && std::is_signed<Src>::value
568 && sizeof(Src) >= 4 && sizeof(Src) < 16,
570 estimateSpaceNeeded(Src value) {
572 // When "value" is the smallest negative, negating it would evoke
573 // undefined behavior, so, instead of writing "-value" below, we write
574 // "~static_cast<uint64_t>(value) + 1"
575 return 1 + digits10(~static_cast<uint64_t>(value) + 1);
578 return digits10(static_cast<uint64_t>(value));
582 * As above, but for uint32_t and uint64_t.
584 template <class Tgt, class Src>
585 typename std::enable_if<
586 std::is_integral<Src>::value && !std::is_signed<Src>::value
587 && IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
588 toAppend(Src value, Tgt * result) {
590 result->append(buffer, uint64ToBufferUnsafe(value, buffer));
594 typename std::enable_if<
595 std::is_integral<Src>::value && !std::is_signed<Src>::value
596 && sizeof(Src) >= 4 && sizeof(Src) < 16,
598 estimateSpaceNeeded(Src value) {
599 return digits10(value);
603 * All small signed and unsigned integers to string go through 32-bit
604 * types int32_t and uint32_t, respectively.
606 template <class Tgt, class Src>
607 typename std::enable_if<
608 std::is_integral<Src>::value
609 && IsSomeString<Tgt>::value && sizeof(Src) < 4>::type
610 toAppend(Src value, Tgt * result) {
612 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
614 toAppend<Tgt>(static_cast<Intermediate>(value), result);
618 typename std::enable_if<
619 std::is_integral<Src>::value
621 && !std::is_same<Src, char>::value,
623 estimateSpaceNeeded(Src value) {
625 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
627 return estimateSpaceNeeded(static_cast<Intermediate>(value));
631 * Enumerated values get appended as integers.
633 template <class Tgt, class Src>
634 typename std::enable_if<
635 std::is_enum<Src>::value && IsSomeString<Tgt>::value>::type
636 toAppend(Src value, Tgt * result) {
638 static_cast<typename std::underlying_type<Src>::type>(value), result);
642 typename std::enable_if<
643 std::is_enum<Src>::value, size_t>::type
644 estimateSpaceNeeded(Src value) {
645 return estimateSpaceNeeded(
646 static_cast<typename std::underlying_type<Src>::type>(value));
649 /*******************************************************************************
650 * Conversions from floating-point types to string types.
651 ******************************************************************************/
654 constexpr int kConvMaxDecimalInShortestLow = -6;
655 constexpr int kConvMaxDecimalInShortestHigh = 21;
658 /** Wrapper around DoubleToStringConverter **/
659 template <class Tgt, class Src>
660 typename std::enable_if<
661 std::is_floating_point<Src>::value
662 && IsSomeString<Tgt>::value>::type
666 double_conversion::DoubleToStringConverter::DtoaMode mode,
667 unsigned int numDigits) {
668 using namespace double_conversion;
669 DoubleToStringConverter
670 conv(DoubleToStringConverter::NO_FLAGS,
671 "Infinity", "NaN", 'E',
672 detail::kConvMaxDecimalInShortestLow,
673 detail::kConvMaxDecimalInShortestHigh,
674 6, // max leading padding zeros
675 1); // max trailing padding zeros
677 StringBuilder builder(buffer, sizeof(buffer));
679 case DoubleToStringConverter::SHORTEST:
680 conv.ToShortest(value, &builder);
682 case DoubleToStringConverter::FIXED:
683 conv.ToFixed(value, numDigits, &builder);
686 CHECK(mode == DoubleToStringConverter::PRECISION);
687 conv.ToPrecision(value, numDigits, &builder);
690 const size_t length = builder.position();
692 result->append(buffer, length);
696 * As above, but for floating point
698 template <class Tgt, class Src>
699 typename std::enable_if<
700 std::is_floating_point<Src>::value
701 && IsSomeString<Tgt>::value>::type
702 toAppend(Src value, Tgt * result) {
704 value, result, double_conversion::DoubleToStringConverter::SHORTEST, 0);
708 * Upper bound of the length of the output from
709 * DoubleToStringConverter::ToShortest(double, StringBuilder*),
710 * as used in toAppend(double, string*).
713 typename std::enable_if<
714 std::is_floating_point<Src>::value, size_t>::type
715 estimateSpaceNeeded(Src value) {
716 // kBase10MaximalLength is 17. We add 1 for decimal point,
717 // e.g. 10.0/9 is 17 digits and 18 characters, including the decimal point.
718 constexpr int kMaxMantissaSpace =
719 double_conversion::DoubleToStringConverter::kBase10MaximalLength + 1;
720 // strlen("E-") + digits10(numeric_limits<double>::max_exponent10)
721 constexpr int kMaxExponentSpace = 2 + 3;
722 static const int kMaxPositiveSpace = std::max({
723 // E.g. 1.1111111111111111E-100.
724 kMaxMantissaSpace + kMaxExponentSpace,
725 // E.g. 0.000001.1111111111111111, if kConvMaxDecimalInShortestLow is -6.
726 kMaxMantissaSpace - detail::kConvMaxDecimalInShortestLow,
727 // If kConvMaxDecimalInShortestHigh is 21, then 1e21 is the smallest
728 // number > 1 which ToShortest outputs in exponential notation,
729 // so 21 is the longest non-exponential number > 1.
730 detail::kConvMaxDecimalInShortestHigh
732 return kMaxPositiveSpace + (value < 0); // +1 for minus sign, if negative
736 * This can be specialized, together with adding specialization
737 * for estimateSpaceNeed for your type, so that we allocate
738 * as much as you need instead of the default
741 struct HasLengthEstimator : std::false_type {};
744 constexpr typename std::enable_if<
745 !std::is_fundamental<Src>::value
746 #if FOLLY_HAVE_INT128_T
747 // On OSX 10.10, is_fundamental<__int128> is false :-O
748 && !std::is_same<__int128, Src>::value
749 && !std::is_same<unsigned __int128, Src>::value
751 && !IsSomeString<Src>::value
752 && !std::is_convertible<Src, const char*>::value
753 && !std::is_convertible<Src, StringPiece>::value
754 && !std::is_enum<Src>::value
755 && !HasLengthEstimator<Src>::value,
757 estimateSpaceNeeded(const Src&) {
758 return sizeof(Src) + 1; // dumbest best effort ever?
764 typename std::enable_if<IsSomeString<Tgt>::value, size_t>::type
765 estimateSpaceToReserve(size_t sofar, Tgt*) {
769 template <class T, class... Ts>
770 size_t estimateSpaceToReserve(size_t sofar, const T& v, const Ts&... vs) {
771 return estimateSpaceToReserve(sofar + estimateSpaceNeeded(v), vs...);
775 void reserveInTarget(const Ts&...vs) {
776 getLastElement(vs...)->reserve(estimateSpaceToReserve(0, vs...));
779 template<class Delimiter, class...Ts>
780 void reserveInTargetDelim(const Delimiter& d, const Ts&...vs) {
781 static_assert(sizeof...(vs) >= 2, "Needs at least 2 args");
782 size_t fordelim = (sizeof...(vs) - 2) *
783 estimateSpaceToReserve(0, d, static_cast<std::string*>(nullptr));
784 getLastElement(vs...)->reserve(estimateSpaceToReserve(fordelim, vs...));
788 * Variadic base case: append one element
790 template <class T, class Tgt>
791 typename std::enable_if<
792 IsSomeString<typename std::remove_pointer<Tgt>::type>
794 toAppendStrImpl(const T& v, Tgt result) {
798 template <class T, class... Ts>
799 typename std::enable_if<
800 sizeof...(Ts) >= 2 &&
801 IsSomeString<typename std::remove_pointer<
802 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
803 toAppendStrImpl(const T& v, const Ts&... vs) {
804 toAppend(v, getLastElement(vs...));
805 toAppendStrImpl(vs...);
808 template <class Delimiter, class T, class Tgt>
809 typename std::enable_if<
810 IsSomeString<typename std::remove_pointer<Tgt>::type>::value>::type
811 toAppendDelimStrImpl(const Delimiter& /* delim */, const T& v, Tgt result) {
815 template <class Delimiter, class T, class... Ts>
816 typename std::enable_if<
817 sizeof...(Ts) >= 2 &&
818 IsSomeString<typename std::remove_pointer<
819 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
820 toAppendDelimStrImpl(const Delimiter& delim, const T& v, const Ts&... vs) {
821 // we are really careful here, calling toAppend with just one element does
822 // not try to estimate space needed (as we already did that). If we call
823 // toAppend(v, delim, ....) we would do unnecesary size calculation
824 toAppend(v, detail::getLastElement(vs...));
825 toAppend(delim, detail::getLastElement(vs...));
826 toAppendDelimStrImpl(delim, vs...);
832 * Variadic conversion to string. Appends each element in turn.
833 * If we have two or more things to append, we it will not reserve
834 * the space for them and will depend on strings exponential growth.
835 * If you just append once consider using toAppendFit which reserves
836 * the space needed (but does not have exponential as a result).
838 * Custom implementations of toAppend() can be provided in the same namespace as
839 * the type to customize printing. estimateSpaceNeed() may also be provided to
840 * avoid reallocations in toAppendFit():
842 * namespace other_namespace {
844 * template <class String>
845 * void toAppend(const OtherType&, String* out);
848 * size_t estimateSpaceNeeded(const OtherType&);
852 template <class... Ts>
853 typename std::enable_if<
854 sizeof...(Ts) >= 3 &&
855 IsSomeString<typename std::remove_pointer<
856 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
857 toAppend(const Ts&... vs) {
858 ::folly::detail::toAppendStrImpl(vs...);
862 // Special case pid_t on MSVC, because it's a void* rather than an
863 // integral type. We can't do a global special case because this is already
864 // dangerous enough (as most pointers will implicitly convert to a void*)
865 // just doing it for MSVC.
867 void toAppend(const pid_t a, Tgt* res) {
868 toAppend(uint64_t(a), res);
873 * Special version of the call that preallocates exaclty as much memory
874 * as need for arguments to be stored in target. This means we are
875 * not doing exponential growth when we append. If you are using it
876 * in a loop you are aiming at your foot with a big perf-destroying
878 * On the other hand if you are appending to a string once, this
879 * will probably save a few calls to malloc.
881 template <class... Ts>
882 typename std::enable_if<IsSomeString<typename std::remove_pointer<
883 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
884 toAppendFit(const Ts&... vs) {
885 ::folly::detail::reserveInTarget(vs...);
890 void toAppendFit(const Ts&) {}
893 * Variadic base case: do nothing.
896 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppend(
897 Tgt* /* result */) {}
900 * Variadic base case: do nothing.
902 template <class Delimiter, class Tgt>
903 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
904 const Delimiter& /* delim */, Tgt* /* result */) {}
907 * 1 element: same as toAppend.
909 template <class Delimiter, class T, class Tgt>
910 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
911 const Delimiter& /* delim */, const T& v, Tgt* tgt) {
916 * Append to string with a delimiter in between elements. Check out
917 * comments for toAppend for details about memory allocation.
919 template <class Delimiter, class... Ts>
920 typename std::enable_if<
921 sizeof...(Ts) >= 3 &&
922 IsSomeString<typename std::remove_pointer<
923 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
924 toAppendDelim(const Delimiter& delim, const Ts&... vs) {
925 detail::toAppendDelimStrImpl(delim, vs...);
929 * Detail in comment for toAppendFit
931 template <class Delimiter, class... Ts>
932 typename std::enable_if<IsSomeString<typename std::remove_pointer<
933 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
934 toAppendDelimFit(const Delimiter& delim, const Ts&... vs) {
935 detail::reserveInTargetDelim(delim, vs...);
936 toAppendDelim(delim, vs...);
939 template <class De, class Ts>
940 void toAppendDelimFit(const De&, const Ts&) {}
943 * to<SomeString>(v1, v2, ...) uses toAppend() (see below) as back-end
946 template <class Tgt, class... Ts>
947 typename std::enable_if<
948 IsSomeString<Tgt>::value &&
949 (sizeof...(Ts) != 1 ||
950 !std::is_same<Tgt, typename detail::LastElement<const Ts&...>::type>::
953 to(const Ts&... vs) {
955 toAppendFit(vs..., &result);
960 * Special version of to<SomeString> for floating point. When calling
961 * folly::to<SomeString>(double), generic implementation above will
962 * firstly reserve 24 (or 25 when negative value) bytes. This will
963 * introduce a malloc call for most mainstream string implementations.
965 * But for most cases, a floating point doesn't need 24 (or 25) bytes to
966 * be converted as a string.
968 * This special version will not do string reserve.
970 template <class Tgt, class Src>
971 typename std::enable_if<
972 IsSomeString<Tgt>::value && std::is_floating_point<Src>::value,
976 toAppend(value, &result);
981 * toDelim<SomeString>(SomeString str) returns itself.
983 template <class Tgt, class Delim, class Src>
984 typename std::enable_if<IsSomeString<Tgt>::value &&
985 std::is_same<Tgt, Src>::value,
987 toDelim(const Delim& /* delim */, const Src& value) {
992 * toDelim<SomeString>(delim, v1, v2, ...) uses toAppendDelim() as
993 * back-end for all types.
995 template <class Tgt, class Delim, class... Ts>
996 typename std::enable_if<
997 IsSomeString<Tgt>::value &&
998 (sizeof...(Ts) != 1 ||
999 !std::is_same<Tgt, typename detail::LastElement<const Ts&...>::type>::
1002 toDelim(const Delim& delim, const Ts&... vs) {
1004 toAppendDelimFit(delim, vs..., &result);
1008 /*******************************************************************************
1009 * Conversions from string types to integral types.
1010 ******************************************************************************/
1014 Expected<bool, ConversionCode> str_to_bool(StringPiece* src) noexcept;
1016 template <typename T>
1017 Expected<T, ConversionCode> str_to_floating(StringPiece* src) noexcept;
1019 extern template Expected<float, ConversionCode> str_to_floating<float>(
1020 StringPiece* src) noexcept;
1021 extern template Expected<double, ConversionCode> str_to_floating<double>(
1022 StringPiece* src) noexcept;
1024 template <class Tgt>
1025 Expected<Tgt, ConversionCode> digits_to(const char* b, const char* e) noexcept;
1027 extern template Expected<char, ConversionCode> digits_to<char>(
1029 const char*) noexcept;
1030 extern template Expected<signed char, ConversionCode> digits_to<signed char>(
1032 const char*) noexcept;
1033 extern template Expected<unsigned char, ConversionCode>
1034 digits_to<unsigned char>(const char*, const char*) noexcept;
1036 extern template Expected<short, ConversionCode> digits_to<short>(
1038 const char*) noexcept;
1039 extern template Expected<unsigned short, ConversionCode>
1040 digits_to<unsigned short>(const char*, const char*) noexcept;
1042 extern template Expected<int, ConversionCode> digits_to<int>(
1044 const char*) noexcept;
1045 extern template Expected<unsigned int, ConversionCode> digits_to<unsigned int>(
1047 const char*) noexcept;
1049 extern template Expected<long, ConversionCode> digits_to<long>(
1051 const char*) noexcept;
1052 extern template Expected<unsigned long, ConversionCode>
1053 digits_to<unsigned long>(const char*, const char*) noexcept;
1055 extern template Expected<long long, ConversionCode> digits_to<long long>(
1057 const char*) noexcept;
1058 extern template Expected<unsigned long long, ConversionCode>
1059 digits_to<unsigned long long>(const char*, const char*) noexcept;
1061 #if FOLLY_HAVE_INT128_T
1062 extern template Expected<__int128, ConversionCode> digits_to<__int128>(
1064 const char*) noexcept;
1065 extern template Expected<unsigned __int128, ConversionCode>
1066 digits_to<unsigned __int128>(const char*, const char*) noexcept;
1070 Expected<T, ConversionCode> str_to_integral(StringPiece* src) noexcept;
1072 extern template Expected<char, ConversionCode> str_to_integral<char>(
1073 StringPiece* src) noexcept;
1074 extern template Expected<signed char, ConversionCode>
1075 str_to_integral<signed char>(StringPiece* src) noexcept;
1076 extern template Expected<unsigned char, ConversionCode>
1077 str_to_integral<unsigned char>(StringPiece* src) noexcept;
1079 extern template Expected<short, ConversionCode> str_to_integral<short>(
1080 StringPiece* src) noexcept;
1081 extern template Expected<unsigned short, ConversionCode>
1082 str_to_integral<unsigned short>(StringPiece* src) noexcept;
1084 extern template Expected<int, ConversionCode> str_to_integral<int>(
1085 StringPiece* src) noexcept;
1086 extern template Expected<unsigned int, ConversionCode>
1087 str_to_integral<unsigned int>(StringPiece* src) noexcept;
1089 extern template Expected<long, ConversionCode> str_to_integral<long>(
1090 StringPiece* src) noexcept;
1091 extern template Expected<unsigned long, ConversionCode>
1092 str_to_integral<unsigned long>(StringPiece* src) noexcept;
1094 extern template Expected<long long, ConversionCode> str_to_integral<long long>(
1095 StringPiece* src) noexcept;
1096 extern template Expected<unsigned long long, ConversionCode>
1097 str_to_integral<unsigned long long>(StringPiece* src) noexcept;
1099 #if FOLLY_HAVE_INT128_T
1100 extern template Expected<__int128, ConversionCode> str_to_integral<__int128>(
1101 StringPiece* src) noexcept;
1102 extern template Expected<unsigned __int128, ConversionCode>
1103 str_to_integral<unsigned __int128>(StringPiece* src) noexcept;
1106 template <typename T>
1108 enable_if<std::is_same<T, bool>::value, Expected<T, ConversionCode>>::type
1109 convertTo(StringPiece* src) noexcept {
1110 return str_to_bool(src);
1113 template <typename T>
1114 typename std::enable_if<
1115 std::is_floating_point<T>::value,
1116 Expected<T, ConversionCode>>::type
1117 convertTo(StringPiece* src) noexcept {
1118 return str_to_floating<T>(src);
1121 template <typename T>
1122 typename std::enable_if<
1123 std::is_integral<T>::value && !std::is_same<T, bool>::value,
1124 Expected<T, ConversionCode>>::type
1125 convertTo(StringPiece* src) noexcept {
1126 return str_to_integral<T>(src);
1129 } // namespace detail
1132 * String represented as a pair of pointers to char to unsigned
1133 * integrals. Assumes NO whitespace before or after.
1135 template <typename Tgt>
1136 typename std::enable_if<
1137 std::is_integral<Tgt>::value && !std::is_same<Tgt, bool>::value,
1138 Expected<Tgt, ConversionCode>>::type
1139 tryTo(const char* b, const char* e) {
1140 return detail::digits_to<Tgt>(b, e);
1143 template <typename Tgt>
1144 typename std::enable_if<
1145 std::is_integral<Tgt>::value && !std::is_same<Tgt, bool>::value,
1147 to(const char* b, const char* e) {
1148 return tryTo<Tgt>(b, e).thenOrThrow(
1149 [](Tgt res) { return res; },
1150 [=](ConversionCode code) {
1151 return makeConversionError(code, StringPiece(b, e));
1155 /*******************************************************************************
1156 * Conversions from string types to arithmetic types.
1157 ******************************************************************************/
1160 * Parsing strings to numeric types.
1162 template <typename Tgt>
1163 FOLLY_WARN_UNUSED_RESULT inline typename std::enable_if<
1164 std::is_arithmetic<Tgt>::value,
1165 Expected<StringPiece, ConversionCode>>::type
1166 parseTo(StringPiece src, Tgt& out) {
1167 return detail::convertTo<Tgt>(&src).then(
1168 [&](Tgt res) { return void(out = res), src; });
1171 /*******************************************************************************
1172 * Integral / Floating Point to integral / Floating Point
1173 ******************************************************************************/
1178 * Checked conversion from integral to integral. The checks are only
1179 * performed when meaningful, e.g. conversion from int to long goes
1182 template <class Tgt, class Src>
1183 typename std::enable_if<
1184 std::is_integral<Src>::value && !std::is_same<Tgt, Src>::value &&
1185 !std::is_same<Tgt, bool>::value &&
1186 std::is_integral<Tgt>::value,
1187 Expected<Tgt, ConversionCode>>::type
1188 convertTo(const Src& value) noexcept {
1190 std::numeric_limits<Tgt>::max() < std::numeric_limits<Src>::max()) {
1191 if (greater_than<Tgt, std::numeric_limits<Tgt>::max()>(value)) {
1192 return makeUnexpected(ConversionCode::ARITH_POSITIVE_OVERFLOW);
1196 std::is_signed<Src>::value &&
1197 (!std::is_signed<Tgt>::value || sizeof(Src) > sizeof(Tgt))) {
1198 if (less_than<Tgt, std::numeric_limits<Tgt>::min()>(value)) {
1199 return makeUnexpected(ConversionCode::ARITH_NEGATIVE_OVERFLOW);
1202 return static_cast<Tgt>(value);
1206 * Checked conversion from floating to floating. The checks are only
1207 * performed when meaningful, e.g. conversion from float to double goes
1210 template <class Tgt, class Src>
1211 typename std::enable_if<
1212 std::is_floating_point<Tgt>::value && std::is_floating_point<Src>::value &&
1213 !std::is_same<Tgt, Src>::value,
1214 Expected<Tgt, ConversionCode>>::type
1215 convertTo(const Src& value) noexcept {
1217 std::numeric_limits<Tgt>::max() < std::numeric_limits<Src>::max()) {
1218 if (value > std::numeric_limits<Tgt>::max()) {
1219 return makeUnexpected(ConversionCode::ARITH_POSITIVE_OVERFLOW);
1221 if (value < std::numeric_limits<Tgt>::lowest()) {
1222 return makeUnexpected(ConversionCode::ARITH_NEGATIVE_OVERFLOW);
1225 return boost::implicit_cast<Tgt>(value);
1229 * Check if a floating point value can safely be converted to an
1230 * integer value without triggering undefined behaviour.
1232 template <typename Tgt, typename Src>
1233 inline typename std::enable_if<
1234 std::is_floating_point<Src>::value && std::is_integral<Tgt>::value &&
1235 !std::is_same<Tgt, bool>::value,
1237 checkConversion(const Src& value) {
1238 constexpr Src tgtMaxAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::max());
1239 constexpr Src tgtMinAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::min());
1240 if (value >= tgtMaxAsSrc) {
1241 if (value > tgtMaxAsSrc) {
1244 const Src mmax = folly::nextafter(tgtMaxAsSrc, Src());
1245 if (static_cast<Tgt>(value - mmax) >
1246 std::numeric_limits<Tgt>::max() - static_cast<Tgt>(mmax)) {
1249 } else if (std::is_signed<Tgt>::value && value <= tgtMinAsSrc) {
1250 if (value < tgtMinAsSrc) {
1253 const Src mmin = folly::nextafter(tgtMinAsSrc, Src());
1254 if (static_cast<Tgt>(value - mmin) <
1255 std::numeric_limits<Tgt>::min() - static_cast<Tgt>(mmin)) {
1262 // Integers can always safely be converted to floating point values
1263 template <typename Tgt, typename Src>
1264 constexpr typename std::enable_if<
1265 std::is_integral<Src>::value && std::is_floating_point<Tgt>::value,
1267 checkConversion(const Src&) {
1271 // Also, floating point values can always be safely converted to bool
1272 // Per the standard, any floating point value that is not zero will yield true
1273 template <typename Tgt, typename Src>
1274 constexpr typename std::enable_if<
1275 std::is_floating_point<Src>::value && std::is_same<Tgt, bool>::value,
1277 checkConversion(const Src&) {
1282 * Checked conversion from integral to floating point and back. The
1283 * result must be convertible back to the source type without loss of
1284 * precision. This seems Draconian but sometimes is what's needed, and
1285 * complements existing routines nicely. For various rounding
1286 * routines, see <math>.
1288 template <typename Tgt, typename Src>
1289 typename std::enable_if<
1290 (std::is_integral<Src>::value && std::is_floating_point<Tgt>::value) ||
1291 (std::is_floating_point<Src>::value && std::is_integral<Tgt>::value),
1292 Expected<Tgt, ConversionCode>>::type
1293 convertTo(const Src& value) noexcept {
1294 if (LIKELY(checkConversion<Tgt>(value))) {
1295 Tgt result = static_cast<Tgt>(value);
1296 if (LIKELY(checkConversion<Src>(result))) {
1297 Src witness = static_cast<Src>(result);
1298 if (LIKELY(value == witness)) {
1303 return makeUnexpected(ConversionCode::ARITH_LOSS_OF_PRECISION);
1306 template <typename Tgt, typename Src>
1307 inline std::string errorValue(const Src& value) {
1308 #ifdef FOLLY_HAS_RTTI
1309 return to<std::string>("(", demangle(typeid(Tgt)), ") ", value);
1311 return to<std::string>(value);
1315 template <typename Tgt, typename Src>
1316 using IsArithToArith = std::integral_constant<
1318 !std::is_same<Tgt, Src>::value && !std::is_same<Tgt, bool>::value &&
1319 std::is_arithmetic<Src>::value &&
1320 std::is_arithmetic<Tgt>::value>;
1322 } // namespace detail
1324 template <typename Tgt, typename Src>
1325 typename std::enable_if<
1326 detail::IsArithToArith<Tgt, Src>::value,
1327 Expected<Tgt, ConversionCode>>::type
1328 tryTo(const Src& value) noexcept {
1329 return detail::convertTo<Tgt>(value);
1332 template <typename Tgt, typename Src>
1333 typename std::enable_if<detail::IsArithToArith<Tgt, Src>::value, Tgt>::type to(
1335 return tryTo<Tgt>(value).thenOrThrow(
1336 [](Tgt res) { return res; },
1337 [&](ConversionCode e) {
1338 return makeConversionError(e, detail::errorValue<Tgt>(value));
1342 /*******************************************************************************
1343 * Custom Conversions
1345 * Any type can be used with folly::to by implementing parseTo. The
1346 * implementation should be provided in the namespace of the type to facilitate
1347 * argument-dependent lookup:
1349 * namespace other_namespace {
1350 * ::folly::Expected<::folly::StringPiece, SomeErrorCode>
1351 * parseTo(::folly::StringPiece, OtherType&) noexcept;
1353 ******************************************************************************/
1355 FOLLY_WARN_UNUSED_RESULT typename std::enable_if<
1356 std::is_enum<T>::value,
1357 Expected<StringPiece, ConversionCode>>::type
1358 parseTo(StringPiece in, T& out) noexcept {
1359 typename std::underlying_type<T>::type tmp{};
1360 auto restOrError = parseTo(in, tmp);
1361 out = static_cast<T>(tmp); // Harmless if parseTo fails
1365 FOLLY_WARN_UNUSED_RESULT
1366 inline Expected<StringPiece, ConversionCode> parseTo(
1368 StringPiece& out) noexcept {
1370 return StringPiece{in.end(), in.end()};
1373 FOLLY_WARN_UNUSED_RESULT
1374 inline Expected<StringPiece, ConversionCode> parseTo(
1378 out.append(in.data(), in.size()); // TODO try/catch?
1379 return StringPiece{in.end(), in.end()};
1382 FOLLY_WARN_UNUSED_RESULT
1383 inline Expected<StringPiece, ConversionCode> parseTo(
1387 out.append(in.data(), in.size()); // TODO try/catch?
1388 return StringPiece{in.end(), in.end()};
1392 template <typename Tgt>
1393 using ParseToResult = decltype(parseTo(StringPiece{}, std::declval<Tgt&>()));
1395 struct CheckTrailingSpace {
1396 Expected<Unit, ConversionCode> operator()(StringPiece sp) const {
1397 auto e = enforceWhitespaceErr(sp);
1398 if (UNLIKELY(e != ConversionCode::SUCCESS))
1399 return makeUnexpected(e);
1404 template <class Error>
1407 constexpr Expected<Unit, Error> operator()(T&&) const {
1412 // Older versions of the parseTo customization point threw on error and
1413 // returned void. Handle that.
1414 template <class Tgt>
1415 inline typename std::enable_if<
1416 std::is_void<ParseToResult<Tgt>>::value,
1417 Expected<StringPiece, ConversionCode>>::type
1418 parseToWrap(StringPiece sp, Tgt& out) {
1420 return StringPiece(sp.end(), sp.end());
1423 template <class Tgt>
1424 inline typename std::enable_if<
1425 !std::is_void<ParseToResult<Tgt>>::value,
1426 ParseToResult<Tgt>>::type
1427 parseToWrap(StringPiece sp, Tgt& out) {
1428 return parseTo(sp, out);
1431 template <typename Tgt>
1432 using ParseToError = ExpectedErrorType<decltype(
1433 detail::parseToWrap(StringPiece{}, std::declval<Tgt&>()))>;
1435 } // namespace detail
1438 * String or StringPiece to target conversion. Accepts leading and trailing
1439 * whitespace, but no non-space trailing characters.
1442 template <class Tgt>
1443 inline typename std::enable_if<
1444 !std::is_same<StringPiece, Tgt>::value,
1445 Expected<Tgt, detail::ParseToError<Tgt>>>::type
1446 tryTo(StringPiece src) {
1448 using Error = detail::ParseToError<Tgt>;
1449 using Check = typename std::conditional<
1450 std::is_arithmetic<Tgt>::value,
1451 detail::CheckTrailingSpace,
1452 detail::ReturnUnit<Error>>::type;
1453 return parseTo(src, result).then(Check(), [&](Unit) {
1454 return std::move(result);
1458 template <class Tgt>
1460 typename std::enable_if<!std::is_same<StringPiece, Tgt>::value, Tgt>::type
1461 to(StringPiece src) {
1463 using Error = detail::ParseToError<Tgt>;
1464 using Check = typename std::conditional<
1465 std::is_arithmetic<Tgt>::value,
1466 detail::CheckTrailingSpace,
1467 detail::ReturnUnit<Error>>::type;
1468 auto tmp = detail::parseToWrap(src, result);
1470 .thenOrThrow(Check(), [&](Error e) { throw makeConversionError(e, src); })
1472 [&](Unit) { return std::move(result); },
1473 [&](Error e) { throw makeConversionError(e, tmp.value()); });
1477 * tryTo/to that take the strings by pointer so the caller gets information
1478 * about how much of the string was consumed by the conversion. These do not
1479 * check for trailing whitepsace.
1481 template <class Tgt>
1482 Expected<Tgt, detail::ParseToError<Tgt>> tryTo(StringPiece* src) {
1484 return parseTo(*src, result).then([&, src](StringPiece sp) -> Tgt {
1486 return std::move(result);
1490 template <class Tgt>
1491 Tgt to(StringPiece* src) {
1493 using Error = detail::ParseToError<Tgt>;
1494 return parseTo(*src, result)
1496 [&, src](StringPiece sp) -> Tgt {
1498 return std::move(result);
1500 [=](Error e) { return makeConversionError(e, *src); });
1503 /*******************************************************************************
1504 * Enum to anything and back
1505 ******************************************************************************/
1507 template <class Tgt, class Src>
1508 typename std::enable_if<
1509 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value,
1510 Expected<Tgt, ConversionCode>>::type
1511 tryTo(const Src& value) {
1512 using I = typename std::underlying_type<Src>::type;
1513 return tryTo<Tgt>(static_cast<I>(value));
1516 template <class Tgt, class Src>
1517 typename std::enable_if<
1518 std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value,
1520 tryTo(const Src& value) {
1521 using I = typename std::underlying_type<Tgt>::type;
1522 return tryTo<I>(value).then([](I i) { return static_cast<Tgt>(i); });
1525 template <class Tgt, class Src>
1526 typename std::enable_if<
1527 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value,
1529 to(const Src& value) {
1530 return to<Tgt>(static_cast<typename std::underlying_type<Src>::type>(value));
1533 template <class Tgt, class Src>
1534 typename std::enable_if<
1535 std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value, Tgt>::type
1536 to(const Src & value) {
1537 return static_cast<Tgt>(to<typename std::underlying_type<Tgt>::type>(value));
1540 } // namespace folly