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/FBString.h>
43 #include <folly/Likely.h>
44 #include <folly/Range.h>
45 #include <folly/portability/Math.h>
49 class ConversionError : public std::range_error {
51 // Keep this in sync with kErrorStrings in Conv.cpp
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 ConversionError(const std::string& str, Code code)
71 : std::range_error(str), code_(code) {}
73 ConversionError(const char* str, Code code)
74 : std::range_error(str), code_(code) {}
76 Code errorCode() const { return code_; }
84 ConversionError makeConversionError(
85 ConversionError::Code code,
89 inline ConversionError makeConversionError(
90 ConversionError::Code code,
91 const std::string& str) {
92 return makeConversionError(code, str.data(), str.size());
95 inline ConversionError makeConversionError(
96 ConversionError::Code code,
98 return makeConversionError(code, sp.data(), sp.size());
102 * Enforce that the suffix following a number is made up only of whitespace.
104 inline ConversionError::Code enforceWhitespaceErr(StringPiece sp) {
106 if (!std::isspace(c)) {
107 return ConversionError::NON_WHITESPACE_AFTER_END;
110 return ConversionError::SUCCESS;
114 * Keep this implementation around for prettyToDouble().
116 inline void enforceWhitespace(StringPiece sp) {
117 auto err = enforceWhitespaceErr(sp);
118 if (err != ConversionError::SUCCESS) {
119 throw detail::makeConversionError(err, sp);
124 * A simple std::pair-like wrapper to wrap both a value and an error
126 template <typename T>
127 struct ConversionResult {
128 explicit ConversionResult(T v) : value(v) {}
129 explicit ConversionResult(ConversionError::Code e) : error(e) {}
131 bool success() const {
132 return error == ConversionError::SUCCESS;
136 ConversionError::Code error{ConversionError::SUCCESS};
141 * The identity conversion function.
142 * to<T>(T) returns itself for all types T.
144 template <class Tgt, class Src>
145 typename std::enable_if<std::is_same<Tgt, Src>::value, Tgt>::type
146 to(const Src & value) {
150 template <class Tgt, class Src>
151 typename std::enable_if<std::is_same<Tgt, Src>::value, Tgt>::type
153 return std::forward<Src>(value);
156 /*******************************************************************************
158 ******************************************************************************/
163 const T& getLastElement(const T & v) {
167 template <class T, class... Ts>
168 typename std::tuple_element<
170 std::tuple<T, Ts...> >::type const&
171 getLastElement(const T&, const Ts&... vs) {
172 return getLastElement(vs...);
175 // This class exists to specialize away std::tuple_element in the case where we
176 // have 0 template arguments. Without this, Clang/libc++ will blow a
177 // static_assert even if tuple_element is protected by an enable_if.
178 template <class... Ts>
179 struct last_element {
180 typedef typename std::enable_if<
182 typename std::tuple_element<
183 sizeof...(Ts) - 1, std::tuple<Ts...>
188 struct last_element<> {
192 } // namespace detail
194 /*******************************************************************************
195 * Conversions from integral types to string types.
196 ******************************************************************************/
198 #if FOLLY_HAVE_INT128_T
201 template <typename IntegerType>
202 constexpr unsigned int
204 return (unsigned int)(ceil(sizeof(IntegerType) * CHAR_BIT * M_LN2 / M_LN10));
208 unsafeTelescope128(char * buffer, size_t room, unsigned __int128 x) {
209 typedef unsigned __int128 Usrc;
212 while (x >= (Usrc(1) << 64)) { // Using 128-bit division while needed
213 const auto y = x / 10;
214 const auto digit = x % 10;
216 buffer[p--] = '0' + digit;
220 uint64_t xx = x; // Moving to faster 64-bit division thereafter
223 const auto y = xx / 10ULL;
224 const auto digit = xx % 10ULL;
226 buffer[p--] = '0' + digit;
230 buffer[p] = '0' + xx;
239 * Returns the number of digits in the base 10 representation of an
240 * uint64_t. Useful for preallocating buffers and such. It's also used
241 * internally, see below. Measurements suggest that defining a
242 * separate overload for 32-bit integers is not worthwhile.
245 inline uint32_t digits10(uint64_t v) {
248 // For this arch we can get a little help from specialized CPU instructions
249 // which can count leading zeroes; 64 minus that is appx. log (base 2).
250 // Use that to approximate base-10 digits (log_10) and then adjust if needed.
252 // 10^i, defined for i 0 through 19.
253 // This is 20 * 8 == 160 bytes, which fits neatly into 5 cache lines
254 // (assuming a cache line size of 64).
255 static const uint64_t powersOf10[20] FOLLY_ALIGNED(64) = {
275 10000000000000000000UL,
278 // "count leading zeroes" operation not valid; for 0; special case this.
283 // bits is in the ballpark of log_2(v).
284 const uint8_t leadingZeroes = __builtin_clzll(v);
285 const auto bits = 63 - leadingZeroes;
287 // approximate log_10(v) == log_10(2) * bits.
288 // Integer magic below: 77/256 is appx. 0.3010 (log_10(2)).
289 // The +1 is to make this the ceiling of the log_10 estimate.
290 const uint32_t minLength = 1 + ((bits * 77) >> 8);
292 // return that log_10 lower bound, plus adjust if input >= 10^(that bound)
293 // in case there's a small error and we misjudged length.
294 return minLength + (uint32_t) (UNLIKELY (v >= powersOf10[minLength]));
300 if (LIKELY(v < 10)) return result;
301 if (LIKELY(v < 100)) return result + 1;
302 if (LIKELY(v < 1000)) return result + 2;
303 if (LIKELY(v < 10000)) return result + 3;
304 // Skip ahead by 4 orders of magnitude
313 * Copies the ASCII base 10 representation of v into buffer and
314 * returns the number of bytes written. Does NOT append a \0. Assumes
315 * the buffer points to digits10(v) bytes of valid memory. Note that
316 * uint64 needs at most 20 bytes, uint32_t needs at most 10 bytes,
317 * uint16_t needs at most 5 bytes, and so on. Measurements suggest
318 * that defining a separate overload for 32-bit integers is not
321 * This primitive is unsafe because it makes the size assumption and
322 * because it does not add a terminating \0.
325 inline uint32_t uint64ToBufferUnsafe(uint64_t v, char *const buffer) {
326 auto const result = digits10(v);
327 // WARNING: using size_t or pointer arithmetic for pos slows down
328 // the loop below 20x. This is because several 32-bit ops can be
329 // done in parallel, but only fewer 64-bit ones.
330 uint32_t pos = result - 1;
332 // Keep these together so a peephole optimization "sees" them and
333 // computes them in one shot.
334 auto const q = v / 10;
335 auto const r = static_cast<uint32_t>(v % 10);
336 buffer[pos--] = '0' + r;
339 // Last digit is trivial to handle
340 buffer[pos] = static_cast<uint32_t>(v) + '0';
345 * A single char gets appended.
348 void toAppend(char value, Tgt * result) {
353 constexpr typename std::enable_if<
354 std::is_same<T, char>::value,
356 estimateSpaceNeeded(T) {
361 * Everything implicitly convertible to const char* gets appended.
363 template <class Tgt, class Src>
364 typename std::enable_if<
365 std::is_convertible<Src, const char*>::value
366 && IsSomeString<Tgt>::value>::type
367 toAppend(Src value, Tgt * result) {
368 // Treat null pointers like an empty string, as in:
369 // operator<<(std::ostream&, const char*).
370 const char* c = value;
372 result->append(value);
377 typename std::enable_if<
378 std::is_convertible<Src, const char*>::value,
380 estimateSpaceNeeded(Src value) {
381 const char *c = value;
383 return folly::StringPiece(value).size();
389 typename std::enable_if<
390 (std::is_convertible<Src, folly::StringPiece>::value ||
391 IsSomeString<Src>::value) &&
392 !std::is_convertible<Src, const char*>::value,
394 estimateSpaceNeeded(Src value) {
395 return folly::StringPiece(value).size();
399 inline size_t estimateSpaceNeeded(std::nullptr_t /* value */) {
404 typename std::enable_if<
405 std::is_pointer<Src>::value &&
406 IsSomeString<std::remove_pointer<Src>>::value,
408 estimateSpaceNeeded(Src value) {
409 return value->size();
413 * Strings get appended, too.
415 template <class Tgt, class Src>
416 typename std::enable_if<
417 IsSomeString<Src>::value && IsSomeString<Tgt>::value>::type
418 toAppend(const Src& value, Tgt * result) {
419 result->append(value);
423 * and StringPiece objects too
426 typename std::enable_if<
427 IsSomeString<Tgt>::value>::type
428 toAppend(StringPiece value, Tgt * result) {
429 result->append(value.data(), value.size());
433 * There's no implicit conversion from fbstring to other string types,
434 * so make a specialization.
437 typename std::enable_if<
438 IsSomeString<Tgt>::value>::type
439 toAppend(const fbstring& value, Tgt * result) {
440 result->append(value.data(), value.size());
443 #if FOLLY_HAVE_INT128_T
445 * Special handling for 128 bit integers.
450 toAppend(__int128 value, Tgt * result) {
451 typedef unsigned __int128 Usrc;
452 char buffer[detail::digitsEnough<unsigned __int128>() + 1];
456 p = detail::unsafeTelescope128(buffer, sizeof(buffer), -Usrc(value));
459 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
462 result->append(buffer + p, buffer + sizeof(buffer));
467 toAppend(unsigned __int128 value, Tgt * result) {
468 char buffer[detail::digitsEnough<unsigned __int128>()];
471 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
473 result->append(buffer + p, buffer + sizeof(buffer));
477 constexpr typename std::enable_if<
478 std::is_same<T, __int128>::value,
480 estimateSpaceNeeded(T) {
481 return detail::digitsEnough<__int128>();
485 constexpr typename std::enable_if<
486 std::is_same<T, unsigned __int128>::value,
488 estimateSpaceNeeded(T) {
489 return detail::digitsEnough<unsigned __int128>();
495 * int32_t and int64_t to string (by appending) go through here. The
496 * result is APPENDED to a preexisting string passed as the second
497 * parameter. This should be efficient with fbstring because fbstring
498 * incurs no dynamic allocation below 23 bytes and no number has more
499 * than 22 bytes in its textual representation (20 for digits, one for
500 * sign, one for the terminating 0).
502 template <class Tgt, class Src>
503 typename std::enable_if<
504 std::is_integral<Src>::value && std::is_signed<Src>::value &&
505 IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
506 toAppend(Src value, Tgt * result) {
509 result->push_back('-');
510 result->append(buffer, uint64ToBufferUnsafe(-uint64_t(value), buffer));
512 result->append(buffer, uint64ToBufferUnsafe(value, buffer));
517 typename std::enable_if<
518 std::is_integral<Src>::value && std::is_signed<Src>::value
519 && sizeof(Src) >= 4 && sizeof(Src) < 16,
521 estimateSpaceNeeded(Src value) {
523 // When "value" is the smallest negative, negating it would evoke
524 // undefined behavior, so, instead of writing "-value" below, we write
525 // "~static_cast<uint64_t>(value) + 1"
526 return 1 + digits10(~static_cast<uint64_t>(value) + 1);
529 return digits10(static_cast<uint64_t>(value));
533 * As above, but for uint32_t and uint64_t.
535 template <class Tgt, class Src>
536 typename std::enable_if<
537 std::is_integral<Src>::value && !std::is_signed<Src>::value
538 && IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
539 toAppend(Src value, Tgt * result) {
541 result->append(buffer, uint64ToBufferUnsafe(value, buffer));
545 typename std::enable_if<
546 std::is_integral<Src>::value && !std::is_signed<Src>::value
547 && sizeof(Src) >= 4 && sizeof(Src) < 16,
549 estimateSpaceNeeded(Src value) {
550 return digits10(value);
554 * All small signed and unsigned integers to string go through 32-bit
555 * types int32_t and uint32_t, respectively.
557 template <class Tgt, class Src>
558 typename std::enable_if<
559 std::is_integral<Src>::value
560 && IsSomeString<Tgt>::value && sizeof(Src) < 4>::type
561 toAppend(Src value, Tgt * result) {
563 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
565 toAppend<Tgt>(static_cast<Intermediate>(value), result);
569 typename std::enable_if<
570 std::is_integral<Src>::value
572 && !std::is_same<Src, char>::value,
574 estimateSpaceNeeded(Src value) {
576 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
578 return estimateSpaceNeeded(static_cast<Intermediate>(value));
582 * Enumerated values get appended as integers.
584 template <class Tgt, class Src>
585 typename std::enable_if<
586 std::is_enum<Src>::value && IsSomeString<Tgt>::value>::type
587 toAppend(Src value, Tgt * result) {
589 static_cast<typename std::underlying_type<Src>::type>(value), result);
593 typename std::enable_if<
594 std::is_enum<Src>::value, size_t>::type
595 estimateSpaceNeeded(Src value) {
596 return estimateSpaceNeeded(
597 static_cast<typename std::underlying_type<Src>::type>(value));
600 /*******************************************************************************
601 * Conversions from floating-point types to string types.
602 ******************************************************************************/
605 constexpr int kConvMaxDecimalInShortestLow = -6;
606 constexpr int kConvMaxDecimalInShortestHigh = 21;
609 /** Wrapper around DoubleToStringConverter **/
610 template <class Tgt, class Src>
611 typename std::enable_if<
612 std::is_floating_point<Src>::value
613 && IsSomeString<Tgt>::value>::type
617 double_conversion::DoubleToStringConverter::DtoaMode mode,
618 unsigned int numDigits) {
619 using namespace double_conversion;
620 DoubleToStringConverter
621 conv(DoubleToStringConverter::NO_FLAGS,
622 "Infinity", "NaN", 'E',
623 detail::kConvMaxDecimalInShortestLow,
624 detail::kConvMaxDecimalInShortestHigh,
625 6, // max leading padding zeros
626 1); // max trailing padding zeros
628 StringBuilder builder(buffer, sizeof(buffer));
630 case DoubleToStringConverter::SHORTEST:
631 conv.ToShortest(value, &builder);
633 case DoubleToStringConverter::FIXED:
634 conv.ToFixed(value, numDigits, &builder);
637 CHECK(mode == DoubleToStringConverter::PRECISION);
638 conv.ToPrecision(value, numDigits, &builder);
641 const size_t length = builder.position();
643 result->append(buffer, length);
647 * As above, but for floating point
649 template <class Tgt, class Src>
650 typename std::enable_if<
651 std::is_floating_point<Src>::value
652 && IsSomeString<Tgt>::value>::type
653 toAppend(Src value, Tgt * result) {
655 value, result, double_conversion::DoubleToStringConverter::SHORTEST, 0);
659 * Upper bound of the length of the output from
660 * DoubleToStringConverter::ToShortest(double, StringBuilder*),
661 * as used in toAppend(double, string*).
664 typename std::enable_if<
665 std::is_floating_point<Src>::value, size_t>::type
666 estimateSpaceNeeded(Src value) {
667 // kBase10MaximalLength is 17. We add 1 for decimal point,
668 // e.g. 10.0/9 is 17 digits and 18 characters, including the decimal point.
669 constexpr int kMaxMantissaSpace =
670 double_conversion::DoubleToStringConverter::kBase10MaximalLength + 1;
671 // strlen("E-") + digits10(numeric_limits<double>::max_exponent10)
672 constexpr int kMaxExponentSpace = 2 + 3;
673 static const int kMaxPositiveSpace = std::max({
674 // E.g. 1.1111111111111111E-100.
675 kMaxMantissaSpace + kMaxExponentSpace,
676 // E.g. 0.000001.1111111111111111, if kConvMaxDecimalInShortestLow is -6.
677 kMaxMantissaSpace - detail::kConvMaxDecimalInShortestLow,
678 // If kConvMaxDecimalInShortestHigh is 21, then 1e21 is the smallest
679 // number > 1 which ToShortest outputs in exponential notation,
680 // so 21 is the longest non-exponential number > 1.
681 detail::kConvMaxDecimalInShortestHigh
683 return kMaxPositiveSpace + (value < 0); // +1 for minus sign, if negative
687 * This can be specialized, together with adding specialization
688 * for estimateSpaceNeed for your type, so that we allocate
689 * as much as you need instead of the default
692 struct HasLengthEstimator : std::false_type {};
695 constexpr typename std::enable_if<
696 !std::is_fundamental<Src>::value
697 #if FOLLY_HAVE_INT128_T
698 // On OSX 10.10, is_fundamental<__int128> is false :-O
699 && !std::is_same<__int128, Src>::value
700 && !std::is_same<unsigned __int128, Src>::value
702 && !IsSomeString<Src>::value
703 && !std::is_convertible<Src, const char*>::value
704 && !std::is_convertible<Src, StringPiece>::value
705 && !std::is_enum<Src>::value
706 && !HasLengthEstimator<Src>::value,
708 estimateSpaceNeeded(const Src&) {
709 return sizeof(Src) + 1; // dumbest best effort ever?
715 typename std::enable_if<IsSomeString<Tgt>::value, size_t>::type
716 estimateSpaceToReserve(size_t sofar, Tgt*) {
720 template <class T, class... Ts>
721 size_t estimateSpaceToReserve(size_t sofar, const T& v, const Ts&... vs) {
722 return estimateSpaceToReserve(sofar + estimateSpaceNeeded(v), vs...);
726 void reserveInTarget(const Ts&...vs) {
727 getLastElement(vs...)->reserve(estimateSpaceToReserve(0, vs...));
730 template<class Delimiter, class...Ts>
731 void reserveInTargetDelim(const Delimiter& d, const Ts&...vs) {
732 static_assert(sizeof...(vs) >= 2, "Needs at least 2 args");
733 size_t fordelim = (sizeof...(vs) - 2) *
734 estimateSpaceToReserve(0, d, static_cast<std::string*>(nullptr));
735 getLastElement(vs...)->reserve(estimateSpaceToReserve(fordelim, vs...));
739 * Variadic base case: append one element
741 template <class T, class Tgt>
742 typename std::enable_if<
743 IsSomeString<typename std::remove_pointer<Tgt>::type>
745 toAppendStrImpl(const T& v, Tgt result) {
749 template <class T, class... Ts>
750 typename std::enable_if<sizeof...(Ts) >= 2
752 typename std::remove_pointer<
753 typename detail::last_element<Ts...>::type
754 >::type>::value>::type
755 toAppendStrImpl(const T& v, const Ts&... vs) {
756 toAppend(v, getLastElement(vs...));
757 toAppendStrImpl(vs...);
760 template <class Delimiter, class T, class Tgt>
761 typename std::enable_if<
762 IsSomeString<typename std::remove_pointer<Tgt>::type>::value>::type
763 toAppendDelimStrImpl(const Delimiter& /* delim */, const T& v, Tgt result) {
767 template <class Delimiter, class T, class... Ts>
768 typename std::enable_if<sizeof...(Ts) >= 2
770 typename std::remove_pointer<
771 typename detail::last_element<Ts...>::type
772 >::type>::value>::type
773 toAppendDelimStrImpl(const Delimiter& delim, const T& v, const Ts&... vs) {
774 // we are really careful here, calling toAppend with just one element does
775 // not try to estimate space needed (as we already did that). If we call
776 // toAppend(v, delim, ....) we would do unnecesary size calculation
777 toAppend(v, detail::getLastElement(vs...));
778 toAppend(delim, detail::getLastElement(vs...));
779 toAppendDelimStrImpl(delim, vs...);
785 * Variadic conversion to string. Appends each element in turn.
786 * If we have two or more things to append, we it will not reserve
787 * the space for them and will depend on strings exponential growth.
788 * If you just append once consider using toAppendFit which reserves
789 * the space needed (but does not have exponential as a result).
791 * Custom implementations of toAppend() can be provided in the same namespace as
792 * the type to customize printing. estimateSpaceNeed() may also be provided to
793 * avoid reallocations in toAppendFit():
795 * namespace other_namespace {
797 * template <class String>
798 * void toAppend(const OtherType&, String* out);
801 * size_t estimateSpaceNeeded(const OtherType&);
805 template <class... Ts>
806 typename std::enable_if<sizeof...(Ts) >= 3
808 typename std::remove_pointer<
809 typename detail::last_element<Ts...>::type
810 >::type>::value>::type
811 toAppend(const Ts&... vs) {
812 ::folly::detail::toAppendStrImpl(vs...);
816 // Special case pid_t on MSVC, because it's a void* rather than an
817 // integral type. We can't do a global special case because this is already
818 // dangerous enough (as most pointers will implicitly convert to a void*)
819 // just doing it for MSVC.
821 void toAppend(const pid_t a, Tgt* res) {
822 toAppend(uint64_t(a), res);
827 * Special version of the call that preallocates exaclty as much memory
828 * as need for arguments to be stored in target. This means we are
829 * not doing exponential growth when we append. If you are using it
830 * in a loop you are aiming at your foot with a big perf-destroying
832 * On the other hand if you are appending to a string once, this
833 * will probably save a few calls to malloc.
835 template <class... Ts>
836 typename std::enable_if<
838 typename std::remove_pointer<
839 typename detail::last_element<Ts...>::type
840 >::type>::value>::type
841 toAppendFit(const Ts&... vs) {
842 ::folly::detail::reserveInTarget(vs...);
847 void toAppendFit(const Ts&) {}
850 * Variadic base case: do nothing.
853 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppend(
854 Tgt* /* result */) {}
857 * Variadic base case: do nothing.
859 template <class Delimiter, class Tgt>
860 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
861 const Delimiter& /* delim */, Tgt* /* result */) {}
864 * 1 element: same as toAppend.
866 template <class Delimiter, class T, class Tgt>
867 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
868 const Delimiter& /* delim */, const T& v, Tgt* tgt) {
873 * Append to string with a delimiter in between elements. Check out
874 * comments for toAppend for details about memory allocation.
876 template <class Delimiter, class... Ts>
877 typename std::enable_if<sizeof...(Ts) >= 3
879 typename std::remove_pointer<
880 typename detail::last_element<Ts...>::type
881 >::type>::value>::type
882 toAppendDelim(const Delimiter& delim, const Ts&... vs) {
883 detail::toAppendDelimStrImpl(delim, vs...);
887 * Detail in comment for toAppendFit
889 template <class Delimiter, class... Ts>
890 typename std::enable_if<
892 typename std::remove_pointer<
893 typename detail::last_element<Ts...>::type
894 >::type>::value>::type
895 toAppendDelimFit(const Delimiter& delim, const Ts&... vs) {
896 detail::reserveInTargetDelim(delim, vs...);
897 toAppendDelim(delim, vs...);
900 template <class De, class Ts>
901 void toAppendDelimFit(const De&, const Ts&) {}
904 * to<SomeString>(v1, v2, ...) uses toAppend() (see below) as back-end
907 template <class Tgt, class... Ts>
908 typename std::enable_if<
909 IsSomeString<Tgt>::value && (
910 sizeof...(Ts) != 1 ||
911 !std::is_same<Tgt, typename detail::last_element<Ts...>::type>::value),
913 to(const Ts&... vs) {
915 toAppendFit(vs..., &result);
920 * toDelim<SomeString>(SomeString str) returns itself.
922 template <class Tgt, class Delim, class Src>
923 typename std::enable_if<IsSomeString<Tgt>::value &&
924 std::is_same<Tgt, Src>::value,
926 toDelim(const Delim& /* delim */, const Src& value) {
931 * toDelim<SomeString>(delim, v1, v2, ...) uses toAppendDelim() as
932 * back-end for all types.
934 template <class Tgt, class Delim, class... Ts>
935 typename std::enable_if<
936 IsSomeString<Tgt>::value && (
937 sizeof...(Ts) != 1 ||
938 !std::is_same<Tgt, typename detail::last_element<Ts...>::type>::value),
940 toDelim(const Delim& delim, const Ts&... vs) {
942 toAppendDelimFit(delim, vs..., &result);
946 /*******************************************************************************
947 * Conversions from string types to integral types.
948 ******************************************************************************/
952 ConversionResult<bool> str_to_bool(StringPiece* src);
954 template <typename T>
955 ConversionResult<T> str_to_floating(StringPiece* src);
957 extern template ConversionResult<float> str_to_floating<float>(
959 extern template ConversionResult<double> str_to_floating<double>(
963 ConversionResult<Tgt> digits_to(const char* b, const char* e);
965 extern template ConversionResult<char> digits_to<char>(
968 extern template ConversionResult<signed char> digits_to<signed char>(
971 extern template ConversionResult<unsigned char> digits_to<unsigned char>(
975 extern template ConversionResult<short> digits_to<short>(
978 extern template ConversionResult<unsigned short> digits_to<unsigned short>(
982 extern template ConversionResult<int> digits_to<int>(const char*, const char*);
983 extern template ConversionResult<unsigned int> digits_to<unsigned int>(
987 extern template ConversionResult<long> digits_to<long>(
990 extern template ConversionResult<unsigned long> digits_to<unsigned long>(
994 extern template ConversionResult<long long> digits_to<long long>(
997 extern template ConversionResult<unsigned long long>
998 digits_to<unsigned long long>(const char*, const char*);
1000 #if FOLLY_HAVE_INT128_T
1001 extern template ConversionResult<__int128> digits_to<__int128>(
1004 extern template ConversionResult<unsigned __int128>
1005 digits_to<unsigned __int128>(const char*, const char*);
1009 ConversionResult<T> str_to_integral(StringPiece* src);
1011 extern template ConversionResult<char> str_to_integral<char>(StringPiece* src);
1012 extern template ConversionResult<signed char> str_to_integral<signed char>(
1014 extern template ConversionResult<unsigned char> str_to_integral<unsigned char>(
1017 extern template ConversionResult<short> str_to_integral<short>(
1019 extern template ConversionResult<unsigned short>
1020 str_to_integral<unsigned short>(StringPiece* src);
1022 extern template ConversionResult<int> str_to_integral<int>(StringPiece* src);
1023 extern template ConversionResult<unsigned int> str_to_integral<unsigned int>(
1026 extern template ConversionResult<long> str_to_integral<long>(StringPiece* src);
1027 extern template ConversionResult<unsigned long> str_to_integral<unsigned long>(
1030 extern template ConversionResult<long long> str_to_integral<long long>(
1032 extern template ConversionResult<unsigned long long>
1033 str_to_integral<unsigned long long>(StringPiece* src);
1035 #if FOLLY_HAVE_INT128_T
1036 extern template ConversionResult<__int128> str_to_integral<__int128>(
1038 extern template ConversionResult<unsigned __int128>
1039 str_to_integral<unsigned __int128>(StringPiece* src);
1042 template <typename T>
1043 typename std::enable_if<std::is_same<T, bool>::value, ConversionResult<T>>::type
1044 convertTo(StringPiece* src) {
1045 return str_to_bool(src);
1048 template <typename T>
1049 typename std::enable_if<
1050 std::is_floating_point<T>::value, ConversionResult<T>>::type
1051 convertTo(StringPiece* src) {
1052 return str_to_floating<T>(src);
1055 template <typename T>
1056 typename std::enable_if<
1057 std::is_integral<T>::value && !std::is_same<T, bool>::value,
1058 ConversionResult<T>>::type
1059 convertTo(StringPiece* src) {
1060 return str_to_integral<T>(src);
1063 template <typename T>
1064 struct WrapperInfo { using type = T; };
1066 template <typename T, typename Gen>
1067 typename std::enable_if<
1068 std::is_same<typename WrapperInfo<T>::type, T>::value, T>::type
1069 inline wrap(ConversionResult<typename WrapperInfo<T>::type> res, Gen&& gen) {
1070 if (LIKELY(res.success())) {
1073 throw detail::makeConversionError(res.error, gen());
1076 } // namespace detail
1079 * String represented as a pair of pointers to char to unsigned
1080 * integrals. Assumes NO whitespace before or after.
1082 template <typename Tgt>
1083 typename std::enable_if<
1084 std::is_integral<typename detail::WrapperInfo<Tgt>::type>::value &&
1085 !std::is_same<typename detail::WrapperInfo<Tgt>::type, bool>::value,
1087 to(const char* b, const char* e) {
1088 auto res = detail::digits_to<typename detail::WrapperInfo<Tgt>::type>(b, e);
1089 return detail::wrap<Tgt>(res, [&] { return StringPiece(b, e); });
1092 /*******************************************************************************
1093 * Conversions from string types to arithmetic types.
1094 ******************************************************************************/
1097 * Parsing strings to numeric types. These routines differ from
1098 * parseTo(str, numeric) routines in that they take a POINTER TO a StringPiece
1099 * and alter that StringPiece to reflect progress information.
1101 template <typename Tgt>
1102 typename std::enable_if<
1103 std::is_arithmetic<typename detail::WrapperInfo<Tgt>::type>::value>::type
1104 parseTo(StringPiece* src, Tgt& out) {
1105 auto res = detail::convertTo<typename detail::WrapperInfo<Tgt>::type>(src);
1106 out = detail::wrap<Tgt>(res, [&] { return *src; });
1109 template <typename Tgt>
1110 typename std::enable_if<
1111 std::is_arithmetic<typename detail::WrapperInfo<Tgt>::type>::value>::type
1112 parseTo(StringPiece src, Tgt& out) {
1113 auto res = detail::convertTo<typename detail::WrapperInfo<Tgt>::type>(&src);
1114 if (LIKELY(res.success())) {
1115 res.error = detail::enforceWhitespaceErr(src);
1117 out = detail::wrap<Tgt>(res, [&] { return src; });
1120 /*******************************************************************************
1121 * Integral / Floating Point to integral / Floating Point
1122 ******************************************************************************/
1125 * Unchecked conversion from arithmetic to boolean. This is different from the
1126 * other arithmetic conversions because we use the C convention of treating any
1127 * non-zero value as true, instead of range checking.
1129 template <class Tgt, class Src>
1130 typename std::enable_if<
1131 std::is_arithmetic<Src>::value && !std::is_same<Tgt, Src>::value &&
1132 std::is_same<Tgt, bool>::value,
1134 to(const Src& value) {
1135 return value != Src();
1141 * Checked conversion from integral to integral. The checks are only
1142 * performed when meaningful, e.g. conversion from int to long goes
1145 template <class Tgt, class Src>
1146 typename std::enable_if<
1147 std::is_integral<Src>::value && !std::is_same<Tgt, Src>::value &&
1148 !std::is_same<Tgt, bool>::value &&
1149 std::is_integral<Tgt>::value,
1150 ConversionResult<Tgt>>::type
1151 convertTo(const Src& value) {
1153 std::numeric_limits<Tgt>::max() < std::numeric_limits<Src>::max()) {
1154 if (greater_than<Tgt, std::numeric_limits<Tgt>::max()>(value)) {
1155 return ConversionResult<Tgt>(ConversionError::ARITH_POSITIVE_OVERFLOW);
1159 std::is_signed<Src>::value &&
1160 (!std::is_signed<Tgt>::value || sizeof(Src) > sizeof(Tgt))) {
1161 if (less_than<Tgt, std::numeric_limits<Tgt>::min()>(value)) {
1162 return ConversionResult<Tgt>(ConversionError::ARITH_NEGATIVE_OVERFLOW);
1165 return ConversionResult<Tgt>(static_cast<Tgt>(value));
1169 * Checked conversion from floating to floating. The checks are only
1170 * performed when meaningful, e.g. conversion from float to double goes
1173 template <class Tgt, class Src>
1174 typename std::enable_if<
1175 std::is_floating_point<Tgt>::value && std::is_floating_point<Src>::value &&
1176 !std::is_same<Tgt, Src>::value,
1177 ConversionResult<Tgt>>::type
1178 convertTo(const Src& value) {
1180 std::numeric_limits<Tgt>::max() < std::numeric_limits<Src>::max()) {
1181 if (value > std::numeric_limits<Tgt>::max()) {
1182 return ConversionResult<Tgt>(ConversionError::ARITH_POSITIVE_OVERFLOW);
1184 if (value < std::numeric_limits<Tgt>::lowest()) {
1185 return ConversionResult<Tgt>(ConversionError::ARITH_NEGATIVE_OVERFLOW);
1188 return ConversionResult<Tgt>(boost::implicit_cast<Tgt>(value));
1192 * Check if a floating point value can safely be converted to an
1193 * integer value without triggering undefined behaviour.
1195 template <typename Tgt, typename Src>
1196 inline typename std::enable_if<
1197 std::is_floating_point<Src>::value && std::is_integral<Tgt>::value &&
1198 !std::is_same<Tgt, bool>::value,
1200 checkConversion(const Src& value) {
1201 constexpr Src tgtMaxAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::max());
1202 constexpr Src tgtMinAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::min());
1203 if (value >= tgtMaxAsSrc) {
1204 if (value > tgtMaxAsSrc) {
1207 const Src mmax = folly::nextafter(tgtMaxAsSrc, Src());
1208 if (static_cast<Tgt>(value - mmax) >
1209 std::numeric_limits<Tgt>::max() - static_cast<Tgt>(mmax)) {
1212 } else if (std::is_signed<Tgt>::value && value <= tgtMinAsSrc) {
1213 if (value < tgtMinAsSrc) {
1216 const Src mmin = folly::nextafter(tgtMinAsSrc, Src());
1217 if (static_cast<Tgt>(value - mmin) <
1218 std::numeric_limits<Tgt>::min() - static_cast<Tgt>(mmin)) {
1225 // Integers can always safely be converted to floating point values
1226 template <typename Tgt, typename Src>
1227 constexpr typename std::enable_if<
1228 std::is_integral<Src>::value && std::is_floating_point<Tgt>::value,
1230 checkConversion(const Src&) {
1234 // Also, floating point values can always be safely converted to bool
1235 // Per the standard, any floating point value that is not zero will yield true
1236 template <typename Tgt, typename Src>
1237 constexpr typename std::enable_if<
1238 std::is_floating_point<Src>::value && std::is_same<Tgt, bool>::value,
1240 checkConversion(const Src&) {
1245 * Checked conversion from integral to floating point and back. The
1246 * result must be convertible back to the source type without loss of
1247 * precision. This seems Draconian but sometimes is what's needed, and
1248 * complements existing routines nicely. For various rounding
1249 * routines, see <math>.
1251 template <typename Tgt, typename Src>
1252 typename std::enable_if<
1253 (std::is_integral<Src>::value && std::is_floating_point<Tgt>::value) ||
1254 (std::is_floating_point<Src>::value && std::is_integral<Tgt>::value),
1255 ConversionResult<Tgt>>::type
1256 convertTo(const Src& value) {
1257 if (LIKELY(checkConversion<Tgt>(value))) {
1258 Tgt result = static_cast<Tgt>(value);
1259 if (LIKELY(checkConversion<Src>(result))) {
1260 Src witness = static_cast<Src>(result);
1261 if (LIKELY(value == witness)) {
1262 return ConversionResult<Tgt>(result);
1266 return ConversionResult<Tgt>(ConversionError::ARITH_LOSS_OF_PRECISION);
1269 template <typename Tgt, typename Src>
1270 inline std::string errorValue(const Src& value) {
1271 #ifdef FOLLY_HAS_RTTI
1272 return to<std::string>("(", demangle(typeid(Tgt)), ") ", value);
1274 return to<std::string>(value);
1278 template <typename Tgt, typename Src>
1279 using IsArithToArith = std::integral_constant<
1281 !std::is_same<Tgt, Src>::value && !std::is_same<Tgt, bool>::value &&
1282 std::is_arithmetic<Src>::value &&
1283 std::is_arithmetic<Tgt>::value>;
1285 } // namespace detail
1287 template <typename Tgt, typename Src>
1288 typename std::enable_if<
1289 detail::IsArithToArith<
1290 typename detail::WrapperInfo<Tgt>::type, Src>::value, Tgt>::type
1291 to(const Src& value) {
1292 auto res = detail::convertTo<typename detail::WrapperInfo<Tgt>::type>(value);
1293 return detail::wrap<Tgt>(res, [&] {
1294 return detail::errorValue<typename detail::WrapperInfo<Tgt>::type>(value);
1298 /*******************************************************************************
1299 * Custom Conversions
1301 * Any type can be used with folly::to by implementing parseTo. The
1302 * implementation should be provided in the namespace of the type to facilitate
1303 * argument-dependent lookup:
1305 * namespace other_namespace {
1306 * void parseTo(::folly::StringPiece, OtherType&);
1308 ******************************************************************************/
1310 typename std::enable_if<std::is_enum<T>::value>::type
1311 parseTo(StringPiece in, T& out) {
1312 typename std::underlying_type<T>::type tmp;
1314 out = static_cast<T>(tmp);
1317 inline void parseTo(StringPiece in, StringPiece& out) {
1321 inline void parseTo(StringPiece in, std::string& out) {
1323 out.append(in.data(), in.size());
1326 inline void parseTo(StringPiece in, fbstring& out) {
1328 out.append(in.data(), in.size());
1332 * String or StringPiece to target conversion. Accepts leading and trailing
1333 * whitespace, but no non-space trailing characters.
1336 template <class Tgt>
1337 typename std::enable_if<!std::is_same<StringPiece, Tgt>::value, Tgt>::type
1338 to(StringPiece src) {
1340 parseTo(src, result);
1344 template <class Tgt>
1345 Tgt to(StringPiece* src) {
1347 parseTo(src, result);
1351 /*******************************************************************************
1352 * Enum to anything and back
1353 ******************************************************************************/
1355 template <class Tgt, class Src>
1356 typename std::enable_if<
1357 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value, Tgt>::type
1358 to(const Src & value) {
1359 return to<Tgt>(static_cast<typename std::underlying_type<Src>::type>(value));
1362 template <class Tgt, class Src>
1363 typename std::enable_if<
1364 std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value, Tgt>::type
1365 to(const Src & value) {
1366 return static_cast<Tgt>(to<typename std::underlying_type<Tgt>::type>(value));
1369 } // namespace folly