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 <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/Traits.h>
47 #include <folly/Unit.h>
48 #include <folly/portability/Math.h>
52 // Keep this in sync with kErrorStrings in Conv.cpp
53 enum class ConversionCode : unsigned char {
63 STRING_TO_FLOAT_ERROR,
64 NON_WHITESPACE_AFTER_END,
65 ARITH_POSITIVE_OVERFLOW,
66 ARITH_NEGATIVE_OVERFLOW,
67 ARITH_LOSS_OF_PRECISION,
68 NUM_ERROR_CODES, // has to be the last entry
71 struct ConversionErrorBase : std::range_error {
72 using std::range_error::range_error;
75 class ConversionError : public ConversionErrorBase {
77 ConversionError(const std::string& str, ConversionCode code)
78 : ConversionErrorBase(str), code_(code) {}
80 ConversionError(const char* str, ConversionCode code)
81 : ConversionErrorBase(str), code_(code) {}
83 ConversionCode errorCode() const {
91 /*******************************************************************************
92 * Custom Error Translation
94 * Your overloaded parseTo() function can return a custom error code on failure.
95 * ::folly::to() will call makeConversionError to translate that error code into
96 * an object to throw. makeConversionError is found by argument-dependent
97 * lookup. It should have this signature:
99 * namespace other_namespace {
100 * enum YourErrorCode { BAD_ERROR, WORSE_ERROR };
102 * struct YourConversionError : ConversionErrorBase {
103 * YourConversionError(const char* what) : ConversionErrorBase(what) {}
106 * YourConversionError
107 * makeConversionError(YourErrorCode code, ::folly::StringPiece sp) {
109 * return YourConversionError(messageString);
111 ******************************************************************************/
112 ConversionError makeConversionError(ConversionCode code, StringPiece sp);
116 * Enforce that the suffix following a number is made up only of whitespace.
118 inline ConversionCode enforceWhitespaceErr(StringPiece sp) {
120 if (UNLIKELY(!std::isspace(c))) {
121 return ConversionCode::NON_WHITESPACE_AFTER_END;
124 return ConversionCode::SUCCESS;
128 * Keep this implementation around for prettyToDouble().
130 inline void enforceWhitespace(StringPiece sp) {
131 auto err = enforceWhitespaceErr(sp);
132 if (err != ConversionCode::SUCCESS) {
133 throw makeConversionError(err, sp);
139 * The identity conversion function.
140 * tryTo<T>(T) returns itself for all types T.
142 template <class Tgt, class Src>
143 typename std::enable_if<
144 std::is_same<Tgt, typename std::decay<Src>::type>::value,
145 Expected<Tgt, ConversionCode>>::type
147 return std::forward<Src>(value);
150 template <class Tgt, class Src>
151 typename std::enable_if<
152 std::is_same<Tgt, typename std::decay<Src>::type>::value,
155 return std::forward<Src>(value);
158 /*******************************************************************************
159 * Arithmetic to boolean
160 ******************************************************************************/
163 * Unchecked conversion from arithmetic to boolean. This is different from the
164 * other arithmetic conversions because we use the C convention of treating any
165 * non-zero value as true, instead of range checking.
167 template <class Tgt, class Src>
168 typename std::enable_if<
169 std::is_arithmetic<Src>::value && !std::is_same<Tgt, Src>::value &&
170 std::is_same<Tgt, bool>::value,
171 Expected<Tgt, ConversionCode>>::type
172 tryTo(const Src& value) {
173 return value != Src();
176 template <class Tgt, class Src>
177 typename std::enable_if<
178 std::is_arithmetic<Src>::value && !std::is_same<Tgt, Src>::value &&
179 std::is_same<Tgt, bool>::value,
181 to(const Src& value) {
182 return value != Src();
185 /*******************************************************************************
187 ******************************************************************************/
192 // MSVC can't quite figure out the LastElementImpl::call() stuff
193 // in the base implementation, so we have to use tuples instead,
194 // which result in significantly more templates being compiled,
195 // though the runtime performance is the same.
197 template <typename... Ts>
198 auto getLastElement(Ts&&... ts) -> decltype(
199 std::get<sizeof...(Ts)-1>(std::forward_as_tuple(std::forward<Ts>(ts)...))) {
200 return std::get<sizeof...(Ts)-1>(
201 std::forward_as_tuple(std::forward<Ts>(ts)...));
204 inline void getLastElement() {}
206 template <size_t size, typename... Ts>
207 struct LastElementType : std::tuple_element<size - 1, std::tuple<Ts...>> {};
210 struct LastElementType<0> {
214 template <class... Ts>
216 : std::decay<typename LastElementType<sizeof...(Ts), Ts...>::type> {};
218 template <typename... Ts>
219 struct LastElementImpl {
220 static void call(Ignored<Ts>...) {}
223 template <typename Head, typename... Ts>
224 struct LastElementImpl<Head, Ts...> {
225 template <typename Last>
226 static Last call(Ignored<Ts>..., Last&& last) {
227 return std::forward<Last>(last);
231 template <typename... Ts>
232 auto getLastElement(const Ts&... ts)
233 -> decltype(LastElementImpl<Ts...>::call(ts...)) {
234 return LastElementImpl<Ts...>::call(ts...);
237 template <class... Ts>
238 struct LastElement : std::decay<decltype(
239 LastElementImpl<Ts...>::call(std::declval<Ts>()...))> {
243 } // namespace detail
245 /*******************************************************************************
246 * Conversions from integral types to string types.
247 ******************************************************************************/
249 #if FOLLY_HAVE_INT128_T
252 template <typename IntegerType>
253 constexpr unsigned int
255 return (unsigned int)(ceil(sizeof(IntegerType) * CHAR_BIT * M_LN2 / M_LN10));
259 unsafeTelescope128(char * buffer, size_t room, unsigned __int128 x) {
260 typedef unsigned __int128 Usrc;
263 while (x >= (Usrc(1) << 64)) { // Using 128-bit division while needed
264 const auto y = x / 10;
265 const auto digit = x % 10;
267 buffer[p--] = '0' + digit;
271 uint64_t xx = x; // Moving to faster 64-bit division thereafter
274 const auto y = xx / 10ULL;
275 const auto digit = xx % 10ULL;
277 buffer[p--] = '0' + digit;
281 buffer[p] = '0' + xx;
290 * Returns the number of digits in the base 10 representation of an
291 * uint64_t. Useful for preallocating buffers and such. It's also used
292 * internally, see below. Measurements suggest that defining a
293 * separate overload for 32-bit integers is not worthwhile.
296 inline uint32_t digits10(uint64_t v) {
299 // For this arch we can get a little help from specialized CPU instructions
300 // which can count leading zeroes; 64 minus that is appx. log (base 2).
301 // Use that to approximate base-10 digits (log_10) and then adjust if needed.
303 // 10^i, defined for i 0 through 19.
304 // This is 20 * 8 == 160 bytes, which fits neatly into 5 cache lines
305 // (assuming a cache line size of 64).
306 static const uint64_t powersOf10[20] FOLLY_ALIGNED(64) = {
326 10000000000000000000UL,
329 // "count leading zeroes" operation not valid; for 0; special case this.
334 // bits is in the ballpark of log_2(v).
335 const uint8_t leadingZeroes = __builtin_clzll(v);
336 const auto bits = 63 - leadingZeroes;
338 // approximate log_10(v) == log_10(2) * bits.
339 // Integer magic below: 77/256 is appx. 0.3010 (log_10(2)).
340 // The +1 is to make this the ceiling of the log_10 estimate.
341 const uint32_t minLength = 1 + ((bits * 77) >> 8);
343 // return that log_10 lower bound, plus adjust if input >= 10^(that bound)
344 // in case there's a small error and we misjudged length.
345 return minLength + (uint32_t) (UNLIKELY (v >= powersOf10[minLength]));
351 if (LIKELY(v < 10)) return result;
352 if (LIKELY(v < 100)) return result + 1;
353 if (LIKELY(v < 1000)) return result + 2;
354 if (LIKELY(v < 10000)) return result + 3;
355 // Skip ahead by 4 orders of magnitude
364 * Copies the ASCII base 10 representation of v into buffer and
365 * returns the number of bytes written. Does NOT append a \0. Assumes
366 * the buffer points to digits10(v) bytes of valid memory. Note that
367 * uint64 needs at most 20 bytes, uint32_t needs at most 10 bytes,
368 * uint16_t needs at most 5 bytes, and so on. Measurements suggest
369 * that defining a separate overload for 32-bit integers is not
372 * This primitive is unsafe because it makes the size assumption and
373 * because it does not add a terminating \0.
376 inline uint32_t uint64ToBufferUnsafe(uint64_t v, char *const buffer) {
377 auto const result = digits10(v);
378 // WARNING: using size_t or pointer arithmetic for pos slows down
379 // the loop below 20x. This is because several 32-bit ops can be
380 // done in parallel, but only fewer 64-bit ones.
381 uint32_t pos = result - 1;
383 // Keep these together so a peephole optimization "sees" them and
384 // computes them in one shot.
385 auto const q = v / 10;
386 auto const r = static_cast<char>(v % 10);
387 buffer[pos--] = '0' + r;
390 // Last digit is trivial to handle
391 buffer[pos] = static_cast<char>(v) + '0';
396 * A single char gets appended.
399 void toAppend(char value, Tgt * result) {
404 constexpr typename std::enable_if<
405 std::is_same<T, char>::value,
407 estimateSpaceNeeded(T) {
412 constexpr size_t estimateSpaceNeeded(const char (&)[N]) {
417 * Everything implicitly convertible to const char* gets appended.
419 template <class Tgt, class Src>
420 typename std::enable_if<
421 std::is_convertible<Src, const char*>::value
422 && IsSomeString<Tgt>::value>::type
423 toAppend(Src value, Tgt * result) {
424 // Treat null pointers like an empty string, as in:
425 // operator<<(std::ostream&, const char*).
426 const char* c = value;
428 result->append(value);
433 typename std::enable_if<std::is_convertible<Src, const char*>::value, size_t>::
435 estimateSpaceNeeded(Src value) {
436 const char *c = value;
438 return folly::StringPiece(value).size();
444 typename std::enable_if<
445 (std::is_convertible<Src, folly::StringPiece>::value ||
446 IsSomeString<Src>::value) &&
447 !std::is_convertible<Src, const char*>::value,
449 estimateSpaceNeeded(Src value) {
450 return folly::StringPiece(value).size();
454 inline size_t estimateSpaceNeeded(std::nullptr_t /* value */) {
459 typename std::enable_if<
460 std::is_pointer<Src>::value &&
461 IsSomeString<std::remove_pointer<Src>>::value,
463 estimateSpaceNeeded(Src value) {
464 return value->size();
468 * Strings get appended, too.
470 template <class Tgt, class Src>
471 typename std::enable_if<
472 IsSomeString<Src>::value && IsSomeString<Tgt>::value>::type
473 toAppend(const Src& value, Tgt * result) {
474 result->append(value);
478 * and StringPiece objects too
481 typename std::enable_if<
482 IsSomeString<Tgt>::value>::type
483 toAppend(StringPiece value, Tgt * result) {
484 result->append(value.data(), value.size());
488 * There's no implicit conversion from fbstring to other string types,
489 * so make a specialization.
492 typename std::enable_if<
493 IsSomeString<Tgt>::value>::type
494 toAppend(const fbstring& value, Tgt * result) {
495 result->append(value.data(), value.size());
498 #if FOLLY_HAVE_INT128_T
500 * Special handling for 128 bit integers.
505 toAppend(__int128 value, Tgt * result) {
506 typedef unsigned __int128 Usrc;
507 char buffer[detail::digitsEnough<unsigned __int128>() + 1];
511 p = detail::unsafeTelescope128(buffer, sizeof(buffer), -Usrc(value));
514 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
517 result->append(buffer + p, buffer + sizeof(buffer));
522 toAppend(unsigned __int128 value, Tgt * result) {
523 char buffer[detail::digitsEnough<unsigned __int128>()];
526 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
528 result->append(buffer + p, buffer + sizeof(buffer));
532 constexpr typename std::enable_if<
533 std::is_same<T, __int128>::value,
535 estimateSpaceNeeded(T) {
536 return detail::digitsEnough<__int128>();
540 constexpr typename std::enable_if<
541 std::is_same<T, unsigned __int128>::value,
543 estimateSpaceNeeded(T) {
544 return detail::digitsEnough<unsigned __int128>();
550 * int32_t and int64_t to string (by appending) go through here. The
551 * result is APPENDED to a preexisting string passed as the second
552 * parameter. This should be efficient with fbstring because fbstring
553 * incurs no dynamic allocation below 23 bytes and no number has more
554 * than 22 bytes in its textual representation (20 for digits, one for
555 * sign, one for the terminating 0).
557 template <class Tgt, class Src>
558 typename std::enable_if<
559 std::is_integral<Src>::value && std::is_signed<Src>::value &&
560 IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
561 toAppend(Src value, Tgt * result) {
564 result->push_back('-');
567 uint64ToBufferUnsafe(~static_cast<uint64_t>(value) + 1, buffer));
569 result->append(buffer, uint64ToBufferUnsafe(uint64_t(value), buffer));
574 typename std::enable_if<
575 std::is_integral<Src>::value && std::is_signed<Src>::value
576 && sizeof(Src) >= 4 && sizeof(Src) < 16,
578 estimateSpaceNeeded(Src value) {
580 // When "value" is the smallest negative, negating it would evoke
581 // undefined behavior, so, instead of writing "-value" below, we write
582 // "~static_cast<uint64_t>(value) + 1"
583 return 1 + digits10(~static_cast<uint64_t>(value) + 1);
586 return digits10(static_cast<uint64_t>(value));
590 * As above, but for uint32_t and uint64_t.
592 template <class Tgt, class Src>
593 typename std::enable_if<
594 std::is_integral<Src>::value && !std::is_signed<Src>::value
595 && IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
596 toAppend(Src value, Tgt * result) {
598 result->append(buffer, uint64ToBufferUnsafe(value, buffer));
602 typename std::enable_if<
603 std::is_integral<Src>::value && !std::is_signed<Src>::value
604 && sizeof(Src) >= 4 && sizeof(Src) < 16,
606 estimateSpaceNeeded(Src value) {
607 return digits10(value);
611 * All small signed and unsigned integers to string go through 32-bit
612 * types int32_t and uint32_t, respectively.
614 template <class Tgt, class Src>
615 typename std::enable_if<
616 std::is_integral<Src>::value
617 && IsSomeString<Tgt>::value && sizeof(Src) < 4>::type
618 toAppend(Src value, Tgt * result) {
620 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
622 toAppend<Tgt>(static_cast<Intermediate>(value), result);
626 typename std::enable_if<
627 std::is_integral<Src>::value
629 && !std::is_same<Src, char>::value,
631 estimateSpaceNeeded(Src value) {
633 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
635 return estimateSpaceNeeded(static_cast<Intermediate>(value));
639 * Enumerated values get appended as integers.
641 template <class Tgt, class Src>
642 typename std::enable_if<
643 std::is_enum<Src>::value && IsSomeString<Tgt>::value>::type
644 toAppend(Src value, Tgt * result) {
646 static_cast<typename std::underlying_type<Src>::type>(value), result);
650 typename std::enable_if<
651 std::is_enum<Src>::value, size_t>::type
652 estimateSpaceNeeded(Src value) {
653 return estimateSpaceNeeded(
654 static_cast<typename std::underlying_type<Src>::type>(value));
657 /*******************************************************************************
658 * Conversions from floating-point types to string types.
659 ******************************************************************************/
662 constexpr int kConvMaxDecimalInShortestLow = -6;
663 constexpr int kConvMaxDecimalInShortestHigh = 21;
664 } // namespace detail
666 /** Wrapper around DoubleToStringConverter **/
667 template <class Tgt, class Src>
668 typename std::enable_if<
669 std::is_floating_point<Src>::value
670 && IsSomeString<Tgt>::value>::type
674 double_conversion::DoubleToStringConverter::DtoaMode mode,
675 unsigned int numDigits) {
676 using namespace double_conversion;
677 DoubleToStringConverter
678 conv(DoubleToStringConverter::NO_FLAGS,
679 "Infinity", "NaN", 'E',
680 detail::kConvMaxDecimalInShortestLow,
681 detail::kConvMaxDecimalInShortestHigh,
682 6, // max leading padding zeros
683 1); // max trailing padding zeros
685 StringBuilder builder(buffer, sizeof(buffer));
687 case DoubleToStringConverter::SHORTEST:
688 conv.ToShortest(value, &builder);
690 case DoubleToStringConverter::FIXED:
691 conv.ToFixed(value, int(numDigits), &builder);
694 CHECK(mode == DoubleToStringConverter::PRECISION);
695 conv.ToPrecision(value, int(numDigits), &builder);
698 const size_t length = size_t(builder.position());
700 result->append(buffer, length);
704 * As above, but for floating point
706 template <class Tgt, class Src>
707 typename std::enable_if<
708 std::is_floating_point<Src>::value
709 && IsSomeString<Tgt>::value>::type
710 toAppend(Src value, Tgt * result) {
712 value, result, double_conversion::DoubleToStringConverter::SHORTEST, 0);
716 * Upper bound of the length of the output from
717 * DoubleToStringConverter::ToShortest(double, StringBuilder*),
718 * as used in toAppend(double, string*).
721 typename std::enable_if<
722 std::is_floating_point<Src>::value, size_t>::type
723 estimateSpaceNeeded(Src value) {
724 // kBase10MaximalLength is 17. We add 1 for decimal point,
725 // e.g. 10.0/9 is 17 digits and 18 characters, including the decimal point.
726 constexpr int kMaxMantissaSpace =
727 double_conversion::DoubleToStringConverter::kBase10MaximalLength + 1;
728 // strlen("E-") + digits10(numeric_limits<double>::max_exponent10)
729 constexpr int kMaxExponentSpace = 2 + 3;
730 static const int kMaxPositiveSpace = std::max({
731 // E.g. 1.1111111111111111E-100.
732 kMaxMantissaSpace + kMaxExponentSpace,
733 // E.g. 0.000001.1111111111111111, if kConvMaxDecimalInShortestLow is -6.
734 kMaxMantissaSpace - detail::kConvMaxDecimalInShortestLow,
735 // If kConvMaxDecimalInShortestHigh is 21, then 1e21 is the smallest
736 // number > 1 which ToShortest outputs in exponential notation,
737 // so 21 is the longest non-exponential number > 1.
738 detail::kConvMaxDecimalInShortestHigh
742 (value < 0 ? 1 : 0)); // +1 for minus sign, if negative
746 * This can be specialized, together with adding specialization
747 * for estimateSpaceNeed for your type, so that we allocate
748 * as much as you need instead of the default
751 struct HasLengthEstimator : std::false_type {};
754 constexpr typename std::enable_if<
755 !std::is_fundamental<Src>::value
756 #if FOLLY_HAVE_INT128_T
757 // On OSX 10.10, is_fundamental<__int128> is false :-O
758 && !std::is_same<__int128, Src>::value
759 && !std::is_same<unsigned __int128, Src>::value
761 && !IsSomeString<Src>::value
762 && !std::is_convertible<Src, const char*>::value
763 && !std::is_convertible<Src, StringPiece>::value
764 && !std::is_enum<Src>::value
765 && !HasLengthEstimator<Src>::value,
767 estimateSpaceNeeded(const Src&) {
768 return sizeof(Src) + 1; // dumbest best effort ever?
774 typename std::enable_if<IsSomeString<Tgt>::value, size_t>::type
775 estimateSpaceToReserve(size_t sofar, Tgt*) {
779 template <class T, class... Ts>
780 size_t estimateSpaceToReserve(size_t sofar, const T& v, const Ts&... vs) {
781 return estimateSpaceToReserve(sofar + estimateSpaceNeeded(v), vs...);
784 template <class... Ts>
785 void reserveInTarget(const Ts&...vs) {
786 getLastElement(vs...)->reserve(estimateSpaceToReserve(0, vs...));
789 template <class Delimiter, class... Ts>
790 void reserveInTargetDelim(const Delimiter& d, const Ts&...vs) {
791 static_assert(sizeof...(vs) >= 2, "Needs at least 2 args");
792 size_t fordelim = (sizeof...(vs) - 2) *
793 estimateSpaceToReserve(0, d, static_cast<std::string*>(nullptr));
794 getLastElement(vs...)->reserve(estimateSpaceToReserve(fordelim, vs...));
798 * Variadic base case: append one element
800 template <class T, class Tgt>
801 typename std::enable_if<
802 IsSomeString<typename std::remove_pointer<Tgt>::type>
804 toAppendStrImpl(const T& v, Tgt result) {
808 template <class T, class... Ts>
809 typename std::enable_if<
810 sizeof...(Ts) >= 2 &&
811 IsSomeString<typename std::remove_pointer<
812 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
813 toAppendStrImpl(const T& v, const Ts&... vs) {
814 toAppend(v, getLastElement(vs...));
815 toAppendStrImpl(vs...);
818 template <class Delimiter, class T, class Tgt>
819 typename std::enable_if<
820 IsSomeString<typename std::remove_pointer<Tgt>::type>::value>::type
821 toAppendDelimStrImpl(const Delimiter& /* delim */, const T& v, Tgt result) {
825 template <class Delimiter, class T, class... Ts>
826 typename std::enable_if<
827 sizeof...(Ts) >= 2 &&
828 IsSomeString<typename std::remove_pointer<
829 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
830 toAppendDelimStrImpl(const Delimiter& delim, const T& v, const Ts&... vs) {
831 // we are really careful here, calling toAppend with just one element does
832 // not try to estimate space needed (as we already did that). If we call
833 // toAppend(v, delim, ....) we would do unnecesary size calculation
834 toAppend(v, detail::getLastElement(vs...));
835 toAppend(delim, detail::getLastElement(vs...));
836 toAppendDelimStrImpl(delim, vs...);
838 } // namespace detail
841 * Variadic conversion to string. Appends each element in turn.
842 * If we have two or more things to append, we it will not reserve
843 * the space for them and will depend on strings exponential growth.
844 * If you just append once consider using toAppendFit which reserves
845 * the space needed (but does not have exponential as a result).
847 * Custom implementations of toAppend() can be provided in the same namespace as
848 * the type to customize printing. estimateSpaceNeed() may also be provided to
849 * avoid reallocations in toAppendFit():
851 * namespace other_namespace {
853 * template <class String>
854 * void toAppend(const OtherType&, String* out);
857 * size_t estimateSpaceNeeded(const OtherType&);
861 template <class... Ts>
862 typename std::enable_if<
863 sizeof...(Ts) >= 3 &&
864 IsSomeString<typename std::remove_pointer<
865 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
866 toAppend(const Ts&... vs) {
867 ::folly::detail::toAppendStrImpl(vs...);
871 // Special case pid_t on MSVC, because it's a void* rather than an
872 // integral type. We can't do a global special case because this is already
873 // dangerous enough (as most pointers will implicitly convert to a void*)
874 // just doing it for MSVC.
876 void toAppend(const pid_t a, Tgt* res) {
877 toAppend(uint64_t(a), res);
882 * Special version of the call that preallocates exaclty as much memory
883 * as need for arguments to be stored in target. This means we are
884 * not doing exponential growth when we append. If you are using it
885 * in a loop you are aiming at your foot with a big perf-destroying
887 * On the other hand if you are appending to a string once, this
888 * will probably save a few calls to malloc.
890 template <class... Ts>
891 typename std::enable_if<IsSomeString<typename std::remove_pointer<
892 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
893 toAppendFit(const Ts&... vs) {
894 ::folly::detail::reserveInTarget(vs...);
899 void toAppendFit(const Ts&) {}
902 * Variadic base case: do nothing.
905 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppend(
906 Tgt* /* result */) {}
909 * Variadic base case: do nothing.
911 template <class Delimiter, class Tgt>
912 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
913 const Delimiter& /* delim */, Tgt* /* result */) {}
916 * 1 element: same as toAppend.
918 template <class Delimiter, class T, class Tgt>
919 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
920 const Delimiter& /* delim */, const T& v, Tgt* tgt) {
925 * Append to string with a delimiter in between elements. Check out
926 * comments for toAppend for details about memory allocation.
928 template <class Delimiter, class... Ts>
929 typename std::enable_if<
930 sizeof...(Ts) >= 3 &&
931 IsSomeString<typename std::remove_pointer<
932 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
933 toAppendDelim(const Delimiter& delim, const Ts&... vs) {
934 detail::toAppendDelimStrImpl(delim, vs...);
938 * Detail in comment for toAppendFit
940 template <class Delimiter, class... Ts>
941 typename std::enable_if<IsSomeString<typename std::remove_pointer<
942 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
943 toAppendDelimFit(const Delimiter& delim, const Ts&... vs) {
944 detail::reserveInTargetDelim(delim, vs...);
945 toAppendDelim(delim, vs...);
948 template <class De, class Ts>
949 void toAppendDelimFit(const De&, const Ts&) {}
952 * to<SomeString>(v1, v2, ...) uses toAppend() (see below) as back-end
955 template <class Tgt, class... Ts>
956 typename std::enable_if<
957 IsSomeString<Tgt>::value &&
958 (sizeof...(Ts) != 1 ||
959 !std::is_same<Tgt, typename detail::LastElement<const Ts&...>::type>::
962 to(const Ts&... vs) {
964 toAppendFit(vs..., &result);
969 * Special version of to<SomeString> for floating point. When calling
970 * folly::to<SomeString>(double), generic implementation above will
971 * firstly reserve 24 (or 25 when negative value) bytes. This will
972 * introduce a malloc call for most mainstream string implementations.
974 * But for most cases, a floating point doesn't need 24 (or 25) bytes to
975 * be converted as a string.
977 * This special version will not do string reserve.
979 template <class Tgt, class Src>
980 typename std::enable_if<
981 IsSomeString<Tgt>::value && std::is_floating_point<Src>::value,
985 toAppend(value, &result);
990 * toDelim<SomeString>(SomeString str) returns itself.
992 template <class Tgt, class Delim, class Src>
993 typename std::enable_if<
994 IsSomeString<Tgt>::value &&
995 std::is_same<Tgt, typename std::decay<Src>::type>::value,
997 toDelim(const Delim& /* delim */, Src&& value) {
998 return std::forward<Src>(value);
1002 * toDelim<SomeString>(delim, v1, v2, ...) uses toAppendDelim() as
1003 * back-end for all types.
1005 template <class Tgt, class Delim, class... Ts>
1006 typename std::enable_if<
1007 IsSomeString<Tgt>::value &&
1008 (sizeof...(Ts) != 1 ||
1009 !std::is_same<Tgt, typename detail::LastElement<const Ts&...>::type>::
1012 toDelim(const Delim& delim, const Ts&... vs) {
1014 toAppendDelimFit(delim, vs..., &result);
1018 /*******************************************************************************
1019 * Conversions from string types to integral types.
1020 ******************************************************************************/
1024 Expected<bool, ConversionCode> str_to_bool(StringPiece* src) noexcept;
1026 template <typename T>
1027 Expected<T, ConversionCode> str_to_floating(StringPiece* src) noexcept;
1029 extern template Expected<float, ConversionCode> str_to_floating<float>(
1030 StringPiece* src) noexcept;
1031 extern template Expected<double, ConversionCode> str_to_floating<double>(
1032 StringPiece* src) noexcept;
1034 template <class Tgt>
1035 Expected<Tgt, ConversionCode> digits_to(const char* b, const char* e) noexcept;
1037 extern template Expected<char, ConversionCode> digits_to<char>(
1039 const char*) noexcept;
1040 extern template Expected<signed char, ConversionCode> digits_to<signed char>(
1042 const char*) noexcept;
1043 extern template Expected<unsigned char, ConversionCode>
1044 digits_to<unsigned char>(const char*, const char*) noexcept;
1046 extern template Expected<short, ConversionCode> digits_to<short>(
1048 const char*) noexcept;
1049 extern template Expected<unsigned short, ConversionCode>
1050 digits_to<unsigned short>(const char*, const char*) noexcept;
1052 extern template Expected<int, ConversionCode> digits_to<int>(
1054 const char*) noexcept;
1055 extern template Expected<unsigned int, ConversionCode> digits_to<unsigned int>(
1057 const char*) noexcept;
1059 extern template Expected<long, ConversionCode> digits_to<long>(
1061 const char*) noexcept;
1062 extern template Expected<unsigned long, ConversionCode>
1063 digits_to<unsigned long>(const char*, const char*) noexcept;
1065 extern template Expected<long long, ConversionCode> digits_to<long long>(
1067 const char*) noexcept;
1068 extern template Expected<unsigned long long, ConversionCode>
1069 digits_to<unsigned long long>(const char*, const char*) noexcept;
1071 #if FOLLY_HAVE_INT128_T
1072 extern template Expected<__int128, ConversionCode> digits_to<__int128>(
1074 const char*) noexcept;
1075 extern template Expected<unsigned __int128, ConversionCode>
1076 digits_to<unsigned __int128>(const char*, const char*) noexcept;
1080 Expected<T, ConversionCode> str_to_integral(StringPiece* src) noexcept;
1082 extern template Expected<char, ConversionCode> str_to_integral<char>(
1083 StringPiece* src) noexcept;
1084 extern template Expected<signed char, ConversionCode>
1085 str_to_integral<signed char>(StringPiece* src) noexcept;
1086 extern template Expected<unsigned char, ConversionCode>
1087 str_to_integral<unsigned char>(StringPiece* src) noexcept;
1089 extern template Expected<short, ConversionCode> str_to_integral<short>(
1090 StringPiece* src) noexcept;
1091 extern template Expected<unsigned short, ConversionCode>
1092 str_to_integral<unsigned short>(StringPiece* src) noexcept;
1094 extern template Expected<int, ConversionCode> str_to_integral<int>(
1095 StringPiece* src) noexcept;
1096 extern template Expected<unsigned int, ConversionCode>
1097 str_to_integral<unsigned int>(StringPiece* src) noexcept;
1099 extern template Expected<long, ConversionCode> str_to_integral<long>(
1100 StringPiece* src) noexcept;
1101 extern template Expected<unsigned long, ConversionCode>
1102 str_to_integral<unsigned long>(StringPiece* src) noexcept;
1104 extern template Expected<long long, ConversionCode> str_to_integral<long long>(
1105 StringPiece* src) noexcept;
1106 extern template Expected<unsigned long long, ConversionCode>
1107 str_to_integral<unsigned long long>(StringPiece* src) noexcept;
1109 #if FOLLY_HAVE_INT128_T
1110 extern template Expected<__int128, ConversionCode> str_to_integral<__int128>(
1111 StringPiece* src) noexcept;
1112 extern template Expected<unsigned __int128, ConversionCode>
1113 str_to_integral<unsigned __int128>(StringPiece* src) noexcept;
1116 template <typename T>
1118 enable_if<std::is_same<T, bool>::value, Expected<T, ConversionCode>>::type
1119 convertTo(StringPiece* src) noexcept {
1120 return str_to_bool(src);
1123 template <typename T>
1124 typename std::enable_if<
1125 std::is_floating_point<T>::value,
1126 Expected<T, ConversionCode>>::type
1127 convertTo(StringPiece* src) noexcept {
1128 return str_to_floating<T>(src);
1131 template <typename T>
1132 typename std::enable_if<
1133 std::is_integral<T>::value && !std::is_same<T, bool>::value,
1134 Expected<T, ConversionCode>>::type
1135 convertTo(StringPiece* src) noexcept {
1136 return str_to_integral<T>(src);
1139 } // namespace detail
1142 * String represented as a pair of pointers to char to unsigned
1143 * integrals. Assumes NO whitespace before or after.
1145 template <typename Tgt>
1146 typename std::enable_if<
1147 std::is_integral<Tgt>::value && !std::is_same<Tgt, bool>::value,
1148 Expected<Tgt, ConversionCode>>::type
1149 tryTo(const char* b, const char* e) {
1150 return detail::digits_to<Tgt>(b, e);
1153 template <typename Tgt>
1154 typename std::enable_if<
1155 std::is_integral<Tgt>::value && !std::is_same<Tgt, bool>::value,
1157 to(const char* b, const char* e) {
1158 return tryTo<Tgt>(b, e).thenOrThrow(
1159 [](Tgt res) { return res; },
1160 [=](ConversionCode code) {
1161 return makeConversionError(code, StringPiece(b, e));
1165 /*******************************************************************************
1166 * Conversions from string types to arithmetic types.
1167 ******************************************************************************/
1170 * Parsing strings to numeric types.
1172 template <typename Tgt>
1173 FOLLY_NODISCARD inline typename std::enable_if<
1174 std::is_arithmetic<Tgt>::value,
1175 Expected<StringPiece, ConversionCode>>::type
1176 parseTo(StringPiece src, Tgt& out) {
1177 return detail::convertTo<Tgt>(&src).then(
1178 [&](Tgt res) { return void(out = res), src; });
1181 /*******************************************************************************
1182 * Integral / Floating Point to integral / Floating Point
1183 ******************************************************************************/
1188 * Bool to integral/float doesn't need any special checks, and this
1189 * overload means we aren't trying to see if a bool is less than
1192 template <class Tgt>
1193 typename std::enable_if<
1194 !std::is_same<Tgt, bool>::value &&
1195 (std::is_integral<Tgt>::value || std::is_floating_point<Tgt>::value),
1196 Expected<Tgt, ConversionCode>>::type
1197 convertTo(const bool& value) noexcept {
1198 return static_cast<Tgt>(value ? 1 : 0);
1202 * Checked conversion from integral to integral. The checks are only
1203 * performed when meaningful, e.g. conversion from int to long goes
1206 template <class Tgt, class Src>
1207 typename std::enable_if<
1208 std::is_integral<Src>::value && !std::is_same<Tgt, Src>::value &&
1209 !std::is_same<Tgt, bool>::value &&
1210 std::is_integral<Tgt>::value,
1211 Expected<Tgt, ConversionCode>>::type
1212 convertTo(const Src& value) noexcept {
1214 folly::_t<std::make_unsigned<Tgt>>(std::numeric_limits<Tgt>::max()) <
1215 folly::_t<std::make_unsigned<Src>>(std::numeric_limits<Src>::max())) {
1216 if (greater_than<Tgt, std::numeric_limits<Tgt>::max()>(value)) {
1217 return makeUnexpected(ConversionCode::ARITH_POSITIVE_OVERFLOW);
1221 std::is_signed<Src>::value &&
1222 (!std::is_signed<Tgt>::value || sizeof(Src) > sizeof(Tgt))) {
1223 if (less_than<Tgt, std::numeric_limits<Tgt>::min()>(value)) {
1224 return makeUnexpected(ConversionCode::ARITH_NEGATIVE_OVERFLOW);
1227 return static_cast<Tgt>(value);
1231 * Checked conversion from floating to floating. The checks are only
1232 * performed when meaningful, e.g. conversion from float to double goes
1235 template <class Tgt, class Src>
1236 typename std::enable_if<
1237 std::is_floating_point<Tgt>::value && std::is_floating_point<Src>::value &&
1238 !std::is_same<Tgt, Src>::value,
1239 Expected<Tgt, ConversionCode>>::type
1240 convertTo(const Src& value) noexcept {
1242 std::numeric_limits<Tgt>::max() < std::numeric_limits<Src>::max()) {
1243 if (value > std::numeric_limits<Tgt>::max()) {
1244 return makeUnexpected(ConversionCode::ARITH_POSITIVE_OVERFLOW);
1246 if (value < std::numeric_limits<Tgt>::lowest()) {
1247 return makeUnexpected(ConversionCode::ARITH_NEGATIVE_OVERFLOW);
1250 return static_cast<Tgt>(value);
1254 * Check if a floating point value can safely be converted to an
1255 * integer value without triggering undefined behaviour.
1257 template <typename Tgt, typename Src>
1258 inline typename std::enable_if<
1259 std::is_floating_point<Src>::value && std::is_integral<Tgt>::value &&
1260 !std::is_same<Tgt, bool>::value,
1262 checkConversion(const Src& value) {
1263 constexpr Src tgtMaxAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::max());
1264 constexpr Src tgtMinAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::min());
1265 if (value >= tgtMaxAsSrc) {
1266 if (value > tgtMaxAsSrc) {
1269 const Src mmax = folly::nextafter(tgtMaxAsSrc, Src());
1270 if (static_cast<Tgt>(value - mmax) >
1271 std::numeric_limits<Tgt>::max() - static_cast<Tgt>(mmax)) {
1274 } else if (std::is_signed<Tgt>::value && value <= tgtMinAsSrc) {
1275 if (value < tgtMinAsSrc) {
1278 const Src mmin = folly::nextafter(tgtMinAsSrc, Src());
1279 if (static_cast<Tgt>(value - mmin) <
1280 std::numeric_limits<Tgt>::min() - static_cast<Tgt>(mmin)) {
1287 // Integers can always safely be converted to floating point values
1288 template <typename Tgt, typename Src>
1289 constexpr typename std::enable_if<
1290 std::is_integral<Src>::value && std::is_floating_point<Tgt>::value,
1292 checkConversion(const Src&) {
1296 // Also, floating point values can always be safely converted to bool
1297 // Per the standard, any floating point value that is not zero will yield true
1298 template <typename Tgt, typename Src>
1299 constexpr typename std::enable_if<
1300 std::is_floating_point<Src>::value && std::is_same<Tgt, bool>::value,
1302 checkConversion(const Src&) {
1307 * Checked conversion from integral to floating point and back. The
1308 * result must be convertible back to the source type without loss of
1309 * precision. This seems Draconian but sometimes is what's needed, and
1310 * complements existing routines nicely. For various rounding
1311 * routines, see <math>.
1313 template <typename Tgt, typename Src>
1314 typename std::enable_if<
1315 (std::is_integral<Src>::value && std::is_floating_point<Tgt>::value) ||
1316 (std::is_floating_point<Src>::value && std::is_integral<Tgt>::value),
1317 Expected<Tgt, ConversionCode>>::type
1318 convertTo(const Src& value) noexcept {
1319 if (LIKELY(checkConversion<Tgt>(value))) {
1320 Tgt result = static_cast<Tgt>(value);
1321 if (LIKELY(checkConversion<Src>(result))) {
1322 Src witness = static_cast<Src>(result);
1323 if (LIKELY(value == witness)) {
1328 return makeUnexpected(ConversionCode::ARITH_LOSS_OF_PRECISION);
1331 template <typename Tgt, typename Src>
1332 inline std::string errorValue(const Src& value) {
1333 #ifdef FOLLY_HAS_RTTI
1334 return to<std::string>("(", demangle(typeid(Tgt)), ") ", value);
1336 return to<std::string>(value);
1340 template <typename Tgt, typename Src>
1341 using IsArithToArith = std::integral_constant<
1343 !std::is_same<Tgt, Src>::value && !std::is_same<Tgt, bool>::value &&
1344 std::is_arithmetic<Src>::value &&
1345 std::is_arithmetic<Tgt>::value>;
1347 } // namespace detail
1349 template <typename Tgt, typename Src>
1350 typename std::enable_if<
1351 detail::IsArithToArith<Tgt, Src>::value,
1352 Expected<Tgt, ConversionCode>>::type
1353 tryTo(const Src& value) noexcept {
1354 return detail::convertTo<Tgt>(value);
1357 template <typename Tgt, typename Src>
1358 typename std::enable_if<detail::IsArithToArith<Tgt, Src>::value, Tgt>::type to(
1360 return tryTo<Tgt>(value).thenOrThrow(
1361 [](Tgt res) { return res; },
1362 [&](ConversionCode e) {
1363 return makeConversionError(e, detail::errorValue<Tgt>(value));
1367 /*******************************************************************************
1368 * Custom Conversions
1370 * Any type can be used with folly::to by implementing parseTo. The
1371 * implementation should be provided in the namespace of the type to facilitate
1372 * argument-dependent lookup:
1374 * namespace other_namespace {
1375 * ::folly::Expected<::folly::StringPiece, SomeErrorCode>
1376 * parseTo(::folly::StringPiece, OtherType&) noexcept;
1378 ******************************************************************************/
1380 FOLLY_NODISCARD typename std::enable_if<
1381 std::is_enum<T>::value,
1382 Expected<StringPiece, ConversionCode>>::type
1383 parseTo(StringPiece in, T& out) noexcept {
1384 typename std::underlying_type<T>::type tmp{};
1385 auto restOrError = parseTo(in, tmp);
1386 out = static_cast<T>(tmp); // Harmless if parseTo fails
1391 inline Expected<StringPiece, ConversionCode> parseTo(
1393 StringPiece& out) noexcept {
1395 return StringPiece{in.end(), in.end()};
1399 inline Expected<StringPiece, ConversionCode> parseTo(
1403 out.append(in.data(), in.size()); // TODO try/catch?
1404 return StringPiece{in.end(), in.end()};
1408 inline Expected<StringPiece, ConversionCode> parseTo(
1412 out.append(in.data(), in.size()); // TODO try/catch?
1413 return StringPiece{in.end(), in.end()};
1417 template <typename Tgt>
1418 using ParseToResult = decltype(parseTo(StringPiece{}, std::declval<Tgt&>()));
1420 struct CheckTrailingSpace {
1421 Expected<Unit, ConversionCode> operator()(StringPiece sp) const {
1422 auto e = enforceWhitespaceErr(sp);
1423 if (UNLIKELY(e != ConversionCode::SUCCESS))
1424 return makeUnexpected(e);
1429 template <class Error>
1432 constexpr Expected<Unit, Error> operator()(T&&) const {
1437 // Older versions of the parseTo customization point threw on error and
1438 // returned void. Handle that.
1439 template <class Tgt>
1440 inline typename std::enable_if<
1441 std::is_void<ParseToResult<Tgt>>::value,
1442 Expected<StringPiece, ConversionCode>>::type
1443 parseToWrap(StringPiece sp, Tgt& out) {
1445 return StringPiece(sp.end(), sp.end());
1448 template <class Tgt>
1449 inline typename std::enable_if<
1450 !std::is_void<ParseToResult<Tgt>>::value,
1451 ParseToResult<Tgt>>::type
1452 parseToWrap(StringPiece sp, Tgt& out) {
1453 return parseTo(sp, out);
1456 template <typename Tgt>
1457 using ParseToError = ExpectedErrorType<decltype(
1458 detail::parseToWrap(StringPiece{}, std::declval<Tgt&>()))>;
1460 } // namespace detail
1463 * String or StringPiece to target conversion. Accepts leading and trailing
1464 * whitespace, but no non-space trailing characters.
1467 template <class Tgt>
1468 inline typename std::enable_if<
1469 !std::is_same<StringPiece, Tgt>::value,
1470 Expected<Tgt, detail::ParseToError<Tgt>>>::type
1471 tryTo(StringPiece src) {
1473 using Error = detail::ParseToError<Tgt>;
1474 using Check = typename std::conditional<
1475 std::is_arithmetic<Tgt>::value,
1476 detail::CheckTrailingSpace,
1477 detail::ReturnUnit<Error>>::type;
1478 return parseTo(src, result).then(Check(), [&](Unit) {
1479 return std::move(result);
1483 template <class Tgt>
1485 typename std::enable_if<!std::is_same<StringPiece, Tgt>::value, Tgt>::type
1486 to(StringPiece src) {
1488 using Error = detail::ParseToError<Tgt>;
1489 using Check = typename std::conditional<
1490 std::is_arithmetic<Tgt>::value,
1491 detail::CheckTrailingSpace,
1492 detail::ReturnUnit<Error>>::type;
1493 auto tmp = detail::parseToWrap(src, result);
1495 .thenOrThrow(Check(), [&](Error e) { throw makeConversionError(e, src); })
1497 [&](Unit) { return std::move(result); },
1498 [&](Error e) { throw makeConversionError(e, tmp.value()); });
1502 * tryTo/to that take the strings by pointer so the caller gets information
1503 * about how much of the string was consumed by the conversion. These do not
1504 * check for trailing whitepsace.
1506 template <class Tgt>
1507 Expected<Tgt, detail::ParseToError<Tgt>> tryTo(StringPiece* src) {
1509 return parseTo(*src, result).then([&, src](StringPiece sp) -> Tgt {
1511 return std::move(result);
1515 template <class Tgt>
1516 Tgt to(StringPiece* src) {
1518 using Error = detail::ParseToError<Tgt>;
1519 return parseTo(*src, result)
1521 [&, src](StringPiece sp) -> Tgt {
1523 return std::move(result);
1525 [=](Error e) { return makeConversionError(e, *src); });
1528 /*******************************************************************************
1529 * Enum to anything and back
1530 ******************************************************************************/
1532 template <class Tgt, class Src>
1533 typename std::enable_if<
1534 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value,
1535 Expected<Tgt, ConversionCode>>::type
1536 tryTo(const Src& value) {
1537 using I = typename std::underlying_type<Src>::type;
1538 return tryTo<Tgt>(static_cast<I>(value));
1541 template <class Tgt, class Src>
1542 typename std::enable_if<
1543 std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value,
1544 Expected<Tgt, ConversionCode>>::type
1545 tryTo(const Src& value) {
1546 using I = typename std::underlying_type<Tgt>::type;
1547 return tryTo<I>(value).then([](I i) { return static_cast<Tgt>(i); });
1550 template <class Tgt, class Src>
1551 typename std::enable_if<
1552 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value,
1554 to(const Src& value) {
1555 return to<Tgt>(static_cast<typename std::underlying_type<Src>::type>(value));
1558 template <class Tgt, class Src>
1559 typename std::enable_if<
1560 std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value, Tgt>::type
1561 to(const Src & value) {
1562 return static_cast<Tgt>(to<typename std::underlying_type<Tgt>::type>(value));
1565 } // namespace folly