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 * Ubiquitous helper template for writing string appenders
363 template <class T> struct IsSomeString {
364 enum { value = std::is_same<T, std::string>::value
365 || std::is_same<T, fbstring>::value };
369 * Everything implicitly convertible to const char* gets appended.
371 template <class Tgt, class Src>
372 typename std::enable_if<
373 std::is_convertible<Src, const char*>::value
374 && IsSomeString<Tgt>::value>::type
375 toAppend(Src value, Tgt * result) {
376 // Treat null pointers like an empty string, as in:
377 // operator<<(std::ostream&, const char*).
378 const char* c = value;
380 result->append(value);
385 typename std::enable_if<
386 std::is_convertible<Src, const char*>::value,
388 estimateSpaceNeeded(Src value) {
389 const char *c = value;
391 return folly::StringPiece(value).size();
397 typename std::enable_if<
398 (std::is_convertible<Src, folly::StringPiece>::value ||
399 IsSomeString<Src>::value) &&
400 !std::is_convertible<Src, const char*>::value,
402 estimateSpaceNeeded(Src value) {
403 return folly::StringPiece(value).size();
407 inline size_t estimateSpaceNeeded(std::nullptr_t /* value */) {
412 typename std::enable_if<
413 std::is_pointer<Src>::value &&
414 IsSomeString<std::remove_pointer<Src>>::value,
416 estimateSpaceNeeded(Src value) {
417 return value->size();
421 * Strings get appended, too.
423 template <class Tgt, class Src>
424 typename std::enable_if<
425 IsSomeString<Src>::value && IsSomeString<Tgt>::value>::type
426 toAppend(const Src& value, Tgt * result) {
427 result->append(value);
431 * and StringPiece objects too
434 typename std::enable_if<
435 IsSomeString<Tgt>::value>::type
436 toAppend(StringPiece value, Tgt * result) {
437 result->append(value.data(), value.size());
441 * There's no implicit conversion from fbstring to other string types,
442 * so make a specialization.
445 typename std::enable_if<
446 IsSomeString<Tgt>::value>::type
447 toAppend(const fbstring& value, Tgt * result) {
448 result->append(value.data(), value.size());
451 #if FOLLY_HAVE_INT128_T
453 * Special handling for 128 bit integers.
458 toAppend(__int128 value, Tgt * result) {
459 typedef unsigned __int128 Usrc;
460 char buffer[detail::digitsEnough<unsigned __int128>() + 1];
464 p = detail::unsafeTelescope128(buffer, sizeof(buffer), -Usrc(value));
467 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
470 result->append(buffer + p, buffer + sizeof(buffer));
475 toAppend(unsigned __int128 value, Tgt * result) {
476 char buffer[detail::digitsEnough<unsigned __int128>()];
479 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
481 result->append(buffer + p, buffer + sizeof(buffer));
485 constexpr typename std::enable_if<
486 std::is_same<T, __int128>::value,
488 estimateSpaceNeeded(T) {
489 return detail::digitsEnough<__int128>();
493 constexpr typename std::enable_if<
494 std::is_same<T, unsigned __int128>::value,
496 estimateSpaceNeeded(T) {
497 return detail::digitsEnough<unsigned __int128>();
503 * int32_t and int64_t to string (by appending) go through here. The
504 * result is APPENDED to a preexisting string passed as the second
505 * parameter. This should be efficient with fbstring because fbstring
506 * incurs no dynamic allocation below 23 bytes and no number has more
507 * than 22 bytes in its textual representation (20 for digits, one for
508 * sign, one for the terminating 0).
510 template <class Tgt, class Src>
511 typename std::enable_if<
512 std::is_integral<Src>::value && std::is_signed<Src>::value &&
513 IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
514 toAppend(Src value, Tgt * result) {
517 result->push_back('-');
518 result->append(buffer, uint64ToBufferUnsafe(-uint64_t(value), buffer));
520 result->append(buffer, uint64ToBufferUnsafe(value, buffer));
525 typename std::enable_if<
526 std::is_integral<Src>::value && std::is_signed<Src>::value
527 && sizeof(Src) >= 4 && sizeof(Src) < 16,
529 estimateSpaceNeeded(Src value) {
531 // When "value" is the smallest negative, negating it would evoke
532 // undefined behavior, so, instead of writing "-value" below, we write
533 // "~static_cast<uint64_t>(value) + 1"
534 return 1 + digits10(~static_cast<uint64_t>(value) + 1);
537 return digits10(static_cast<uint64_t>(value));
541 * As above, but for uint32_t and uint64_t.
543 template <class Tgt, class Src>
544 typename std::enable_if<
545 std::is_integral<Src>::value && !std::is_signed<Src>::value
546 && IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
547 toAppend(Src value, Tgt * result) {
549 result->append(buffer, uint64ToBufferUnsafe(value, buffer));
553 typename std::enable_if<
554 std::is_integral<Src>::value && !std::is_signed<Src>::value
555 && sizeof(Src) >= 4 && sizeof(Src) < 16,
557 estimateSpaceNeeded(Src value) {
558 return digits10(value);
562 * All small signed and unsigned integers to string go through 32-bit
563 * types int32_t and uint32_t, respectively.
565 template <class Tgt, class Src>
566 typename std::enable_if<
567 std::is_integral<Src>::value
568 && IsSomeString<Tgt>::value && sizeof(Src) < 4>::type
569 toAppend(Src value, Tgt * result) {
571 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
573 toAppend<Tgt>(static_cast<Intermediate>(value), result);
577 typename std::enable_if<
578 std::is_integral<Src>::value
580 && !std::is_same<Src, char>::value,
582 estimateSpaceNeeded(Src value) {
584 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
586 return estimateSpaceNeeded(static_cast<Intermediate>(value));
590 * Enumerated values get appended as integers.
592 template <class Tgt, class Src>
593 typename std::enable_if<
594 std::is_enum<Src>::value && IsSomeString<Tgt>::value>::type
595 toAppend(Src value, Tgt * result) {
597 static_cast<typename std::underlying_type<Src>::type>(value), result);
601 typename std::enable_if<
602 std::is_enum<Src>::value, size_t>::type
603 estimateSpaceNeeded(Src value) {
604 return estimateSpaceNeeded(
605 static_cast<typename std::underlying_type<Src>::type>(value));
608 /*******************************************************************************
609 * Conversions from floating-point types to string types.
610 ******************************************************************************/
613 constexpr int kConvMaxDecimalInShortestLow = -6;
614 constexpr int kConvMaxDecimalInShortestHigh = 21;
617 /** Wrapper around DoubleToStringConverter **/
618 template <class Tgt, class Src>
619 typename std::enable_if<
620 std::is_floating_point<Src>::value
621 && IsSomeString<Tgt>::value>::type
625 double_conversion::DoubleToStringConverter::DtoaMode mode,
626 unsigned int numDigits) {
627 using namespace double_conversion;
628 DoubleToStringConverter
629 conv(DoubleToStringConverter::NO_FLAGS,
630 "Infinity", "NaN", 'E',
631 detail::kConvMaxDecimalInShortestLow,
632 detail::kConvMaxDecimalInShortestHigh,
633 6, // max leading padding zeros
634 1); // max trailing padding zeros
636 StringBuilder builder(buffer, sizeof(buffer));
638 case DoubleToStringConverter::SHORTEST:
639 conv.ToShortest(value, &builder);
641 case DoubleToStringConverter::FIXED:
642 conv.ToFixed(value, numDigits, &builder);
645 CHECK(mode == DoubleToStringConverter::PRECISION);
646 conv.ToPrecision(value, numDigits, &builder);
649 const size_t length = builder.position();
651 result->append(buffer, length);
655 * As above, but for floating point
657 template <class Tgt, class Src>
658 typename std::enable_if<
659 std::is_floating_point<Src>::value
660 && IsSomeString<Tgt>::value>::type
661 toAppend(Src value, Tgt * result) {
663 value, result, double_conversion::DoubleToStringConverter::SHORTEST, 0);
667 * Upper bound of the length of the output from
668 * DoubleToStringConverter::ToShortest(double, StringBuilder*),
669 * as used in toAppend(double, string*).
672 typename std::enable_if<
673 std::is_floating_point<Src>::value, size_t>::type
674 estimateSpaceNeeded(Src value) {
675 // kBase10MaximalLength is 17. We add 1 for decimal point,
676 // e.g. 10.0/9 is 17 digits and 18 characters, including the decimal point.
677 constexpr int kMaxMantissaSpace =
678 double_conversion::DoubleToStringConverter::kBase10MaximalLength + 1;
679 // strlen("E-") + digits10(numeric_limits<double>::max_exponent10)
680 constexpr int kMaxExponentSpace = 2 + 3;
681 static const int kMaxPositiveSpace = std::max({
682 // E.g. 1.1111111111111111E-100.
683 kMaxMantissaSpace + kMaxExponentSpace,
684 // E.g. 0.000001.1111111111111111, if kConvMaxDecimalInShortestLow is -6.
685 kMaxMantissaSpace - detail::kConvMaxDecimalInShortestLow,
686 // If kConvMaxDecimalInShortestHigh is 21, then 1e21 is the smallest
687 // number > 1 which ToShortest outputs in exponential notation,
688 // so 21 is the longest non-exponential number > 1.
689 detail::kConvMaxDecimalInShortestHigh
691 return kMaxPositiveSpace + (value < 0); // +1 for minus sign, if negative
695 * This can be specialized, together with adding specialization
696 * for estimateSpaceNeed for your type, so that we allocate
697 * as much as you need instead of the default
700 struct HasLengthEstimator : std::false_type {};
703 constexpr typename std::enable_if<
704 !std::is_fundamental<Src>::value
705 #if FOLLY_HAVE_INT128_T
706 // On OSX 10.10, is_fundamental<__int128> is false :-O
707 && !std::is_same<__int128, Src>::value
708 && !std::is_same<unsigned __int128, Src>::value
710 && !IsSomeString<Src>::value
711 && !std::is_convertible<Src, const char*>::value
712 && !std::is_convertible<Src, StringPiece>::value
713 && !std::is_enum<Src>::value
714 && !HasLengthEstimator<Src>::value,
716 estimateSpaceNeeded(const Src&) {
717 return sizeof(Src) + 1; // dumbest best effort ever?
723 typename std::enable_if<IsSomeString<Tgt>::value, size_t>::type
724 estimateSpaceToReserve(size_t sofar, Tgt*) {
728 template <class T, class... Ts>
729 size_t estimateSpaceToReserve(size_t sofar, const T& v, const Ts&... vs) {
730 return estimateSpaceToReserve(sofar + estimateSpaceNeeded(v), vs...);
734 void reserveInTarget(const Ts&...vs) {
735 getLastElement(vs...)->reserve(estimateSpaceToReserve(0, vs...));
738 template<class Delimiter, class...Ts>
739 void reserveInTargetDelim(const Delimiter& d, const Ts&...vs) {
740 static_assert(sizeof...(vs) >= 2, "Needs at least 2 args");
741 size_t fordelim = (sizeof...(vs) - 2) *
742 estimateSpaceToReserve(0, d, static_cast<std::string*>(nullptr));
743 getLastElement(vs...)->reserve(estimateSpaceToReserve(fordelim, vs...));
747 * Variadic base case: append one element
749 template <class T, class Tgt>
750 typename std::enable_if<
751 IsSomeString<typename std::remove_pointer<Tgt>::type>
753 toAppendStrImpl(const T& v, Tgt result) {
757 template <class T, class... Ts>
758 typename std::enable_if<sizeof...(Ts) >= 2
760 typename std::remove_pointer<
761 typename detail::last_element<Ts...>::type
762 >::type>::value>::type
763 toAppendStrImpl(const T& v, const Ts&... vs) {
764 toAppend(v, getLastElement(vs...));
765 toAppendStrImpl(vs...);
768 template <class Delimiter, class T, class Tgt>
769 typename std::enable_if<
770 IsSomeString<typename std::remove_pointer<Tgt>::type>::value>::type
771 toAppendDelimStrImpl(const Delimiter& /* delim */, const T& v, Tgt result) {
775 template <class Delimiter, class T, class... Ts>
776 typename std::enable_if<sizeof...(Ts) >= 2
778 typename std::remove_pointer<
779 typename detail::last_element<Ts...>::type
780 >::type>::value>::type
781 toAppendDelimStrImpl(const Delimiter& delim, const T& v, const Ts&... vs) {
782 // we are really careful here, calling toAppend with just one element does
783 // not try to estimate space needed (as we already did that). If we call
784 // toAppend(v, delim, ....) we would do unnecesary size calculation
785 toAppend(v, detail::getLastElement(vs...));
786 toAppend(delim, detail::getLastElement(vs...));
787 toAppendDelimStrImpl(delim, vs...);
793 * Variadic conversion to string. Appends each element in turn.
794 * If we have two or more things to append, we it will not reserve
795 * the space for them and will depend on strings exponential growth.
796 * If you just append once consider using toAppendFit which reserves
797 * the space needed (but does not have exponential as a result).
799 * Custom implementations of toAppend() can be provided in the same namespace as
800 * the type to customize printing. estimateSpaceNeed() may also be provided to
801 * avoid reallocations in toAppendFit():
803 * namespace other_namespace {
805 * template <class String>
806 * void toAppend(const OtherType&, String* out);
809 * size_t estimateSpaceNeeded(const OtherType&);
813 template <class... Ts>
814 typename std::enable_if<sizeof...(Ts) >= 3
816 typename std::remove_pointer<
817 typename detail::last_element<Ts...>::type
818 >::type>::value>::type
819 toAppend(const Ts&... vs) {
820 ::folly::detail::toAppendStrImpl(vs...);
824 // Special case pid_t on MSVC, because it's a void* rather than an
825 // integral type. We can't do a global special case because this is already
826 // dangerous enough (as most pointers will implicitly convert to a void*)
827 // just doing it for MSVC.
829 void toAppend(const pid_t a, Tgt* res) {
830 toAppend(uint64_t(a), res);
835 * Special version of the call that preallocates exaclty as much memory
836 * as need for arguments to be stored in target. This means we are
837 * not doing exponential growth when we append. If you are using it
838 * in a loop you are aiming at your foot with a big perf-destroying
840 * On the other hand if you are appending to a string once, this
841 * will probably save a few calls to malloc.
843 template <class... Ts>
844 typename std::enable_if<
846 typename std::remove_pointer<
847 typename detail::last_element<Ts...>::type
848 >::type>::value>::type
849 toAppendFit(const Ts&... vs) {
850 ::folly::detail::reserveInTarget(vs...);
855 void toAppendFit(const Ts&) {}
858 * Variadic base case: do nothing.
861 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppend(
862 Tgt* /* result */) {}
865 * Variadic base case: do nothing.
867 template <class Delimiter, class Tgt>
868 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
869 const Delimiter& /* delim */, Tgt* /* result */) {}
872 * 1 element: same as toAppend.
874 template <class Delimiter, class T, class Tgt>
875 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
876 const Delimiter& /* delim */, const T& v, Tgt* tgt) {
881 * Append to string with a delimiter in between elements. Check out
882 * comments for toAppend for details about memory allocation.
884 template <class Delimiter, class... Ts>
885 typename std::enable_if<sizeof...(Ts) >= 3
887 typename std::remove_pointer<
888 typename detail::last_element<Ts...>::type
889 >::type>::value>::type
890 toAppendDelim(const Delimiter& delim, const Ts&... vs) {
891 detail::toAppendDelimStrImpl(delim, vs...);
895 * Detail in comment for toAppendFit
897 template <class Delimiter, class... Ts>
898 typename std::enable_if<
900 typename std::remove_pointer<
901 typename detail::last_element<Ts...>::type
902 >::type>::value>::type
903 toAppendDelimFit(const Delimiter& delim, const Ts&... vs) {
904 detail::reserveInTargetDelim(delim, vs...);
905 toAppendDelim(delim, vs...);
908 template <class De, class Ts>
909 void toAppendDelimFit(const De&, const Ts&) {}
912 * to<SomeString>(v1, v2, ...) uses toAppend() (see below) as back-end
915 template <class Tgt, class... Ts>
916 typename std::enable_if<
917 IsSomeString<Tgt>::value && (
918 sizeof...(Ts) != 1 ||
919 !std::is_same<Tgt, typename detail::last_element<Ts...>::type>::value),
921 to(const Ts&... vs) {
923 toAppendFit(vs..., &result);
928 * toDelim<SomeString>(SomeString str) returns itself.
930 template <class Tgt, class Delim, class Src>
931 typename std::enable_if<IsSomeString<Tgt>::value &&
932 std::is_same<Tgt, Src>::value,
934 toDelim(const Delim& /* delim */, const Src& value) {
939 * toDelim<SomeString>(delim, v1, v2, ...) uses toAppendDelim() as
940 * back-end for all types.
942 template <class Tgt, class Delim, class... Ts>
943 typename std::enable_if<
944 IsSomeString<Tgt>::value && (
945 sizeof...(Ts) != 1 ||
946 !std::is_same<Tgt, typename detail::last_element<Ts...>::type>::value),
948 toDelim(const Delim& delim, const Ts&... vs) {
950 toAppendDelimFit(delim, vs..., &result);
954 /*******************************************************************************
955 * Conversions from string types to integral types.
956 ******************************************************************************/
960 ConversionResult<bool> str_to_bool(StringPiece* src);
962 template <typename T>
963 ConversionResult<T> str_to_floating(StringPiece* src);
965 extern template ConversionResult<float> str_to_floating<float>(
967 extern template ConversionResult<double> str_to_floating<double>(
971 ConversionResult<Tgt> digits_to(const char* b, const char* e);
973 extern template ConversionResult<char> digits_to<char>(
976 extern template ConversionResult<signed char> digits_to<signed char>(
979 extern template ConversionResult<unsigned char> digits_to<unsigned char>(
983 extern template ConversionResult<short> digits_to<short>(
986 extern template ConversionResult<unsigned short> digits_to<unsigned short>(
990 extern template ConversionResult<int> digits_to<int>(const char*, const char*);
991 extern template ConversionResult<unsigned int> digits_to<unsigned int>(
995 extern template ConversionResult<long> digits_to<long>(
998 extern template ConversionResult<unsigned long> digits_to<unsigned long>(
1002 extern template ConversionResult<long long> digits_to<long long>(
1005 extern template ConversionResult<unsigned long long>
1006 digits_to<unsigned long long>(const char*, const char*);
1008 #if FOLLY_HAVE_INT128_T
1009 extern template ConversionResult<__int128> digits_to<__int128>(
1012 extern template ConversionResult<unsigned __int128>
1013 digits_to<unsigned __int128>(const char*, const char*);
1017 ConversionResult<T> str_to_integral(StringPiece* src);
1019 extern template ConversionResult<char> str_to_integral<char>(StringPiece* src);
1020 extern template ConversionResult<signed char> str_to_integral<signed char>(
1022 extern template ConversionResult<unsigned char> str_to_integral<unsigned char>(
1025 extern template ConversionResult<short> str_to_integral<short>(
1027 extern template ConversionResult<unsigned short>
1028 str_to_integral<unsigned short>(StringPiece* src);
1030 extern template ConversionResult<int> str_to_integral<int>(StringPiece* src);
1031 extern template ConversionResult<unsigned int> str_to_integral<unsigned int>(
1034 extern template ConversionResult<long> str_to_integral<long>(StringPiece* src);
1035 extern template ConversionResult<unsigned long> str_to_integral<unsigned long>(
1038 extern template ConversionResult<long long> str_to_integral<long long>(
1040 extern template ConversionResult<unsigned long long>
1041 str_to_integral<unsigned long long>(StringPiece* src);
1043 #if FOLLY_HAVE_INT128_T
1044 extern template ConversionResult<__int128> str_to_integral<__int128>(
1046 extern template ConversionResult<unsigned __int128>
1047 str_to_integral<unsigned __int128>(StringPiece* src);
1050 template <typename T>
1051 typename std::enable_if<std::is_same<T, bool>::value, ConversionResult<T>>::type
1052 convertTo(StringPiece* src) {
1053 return str_to_bool(src);
1056 template <typename T>
1057 typename std::enable_if<
1058 std::is_floating_point<T>::value, ConversionResult<T>>::type
1059 convertTo(StringPiece* src) {
1060 return str_to_floating<T>(src);
1063 template <typename T>
1064 typename std::enable_if<
1065 std::is_integral<T>::value && !std::is_same<T, bool>::value,
1066 ConversionResult<T>>::type
1067 convertTo(StringPiece* src) {
1068 return str_to_integral<T>(src);
1071 template <typename T>
1072 struct WrapperInfo { using type = T; };
1074 template <typename T, typename Gen>
1075 typename std::enable_if<
1076 std::is_same<typename WrapperInfo<T>::type, T>::value, T>::type
1077 inline wrap(ConversionResult<typename WrapperInfo<T>::type> res, Gen&& gen) {
1078 if (LIKELY(res.success())) {
1081 throw detail::makeConversionError(res.error, gen());
1084 } // namespace detail
1087 * String represented as a pair of pointers to char to unsigned
1088 * integrals. Assumes NO whitespace before or after.
1090 template <typename Tgt>
1091 typename std::enable_if<
1092 std::is_integral<typename detail::WrapperInfo<Tgt>::type>::value &&
1093 !std::is_same<typename detail::WrapperInfo<Tgt>::type, bool>::value,
1095 to(const char* b, const char* e) {
1096 auto res = detail::digits_to<typename detail::WrapperInfo<Tgt>::type>(b, e);
1097 return detail::wrap<Tgt>(res, [&] { return StringPiece(b, e); });
1100 /*******************************************************************************
1101 * Conversions from string types to arithmetic types.
1102 ******************************************************************************/
1105 * Parsing strings to numeric types. These routines differ from
1106 * parseTo(str, numeric) routines in that they take a POINTER TO a StringPiece
1107 * and alter that StringPiece to reflect progress information.
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 out = detail::wrap<Tgt>(res, [&] { return *src; });
1117 template <typename Tgt>
1118 typename std::enable_if<
1119 std::is_arithmetic<typename detail::WrapperInfo<Tgt>::type>::value>::type
1120 parseTo(StringPiece src, Tgt& out) {
1121 auto res = detail::convertTo<typename detail::WrapperInfo<Tgt>::type>(&src);
1122 if (LIKELY(res.success())) {
1123 res.error = detail::enforceWhitespaceErr(src);
1125 out = detail::wrap<Tgt>(res, [&] { return src; });
1128 /*******************************************************************************
1129 * Integral / Floating Point to integral / Floating Point
1130 ******************************************************************************/
1133 * Unchecked conversion from arithmetic to boolean. This is different from the
1134 * other arithmetic conversions because we use the C convention of treating any
1135 * non-zero value as true, instead of range checking.
1137 template <class Tgt, class Src>
1138 typename std::enable_if<
1139 std::is_arithmetic<Src>::value && !std::is_same<Tgt, Src>::value &&
1140 std::is_same<Tgt, bool>::value,
1142 to(const Src& value) {
1143 return value != Src();
1149 * Checked conversion from integral to integral. The checks are only
1150 * performed when meaningful, e.g. conversion from int to long goes
1153 template <class Tgt, class Src>
1154 typename std::enable_if<
1155 std::is_integral<Src>::value && !std::is_same<Tgt, Src>::value &&
1156 !std::is_same<Tgt, bool>::value &&
1157 std::is_integral<Tgt>::value,
1158 ConversionResult<Tgt>>::type
1159 convertTo(const Src& value) {
1161 std::numeric_limits<Tgt>::max() < std::numeric_limits<Src>::max()) {
1162 if (greater_than<Tgt, std::numeric_limits<Tgt>::max()>(value)) {
1163 return ConversionResult<Tgt>(ConversionError::ARITH_POSITIVE_OVERFLOW);
1167 std::is_signed<Src>::value &&
1168 (!std::is_signed<Tgt>::value || sizeof(Src) > sizeof(Tgt))) {
1169 if (less_than<Tgt, std::numeric_limits<Tgt>::min()>(value)) {
1170 return ConversionResult<Tgt>(ConversionError::ARITH_NEGATIVE_OVERFLOW);
1173 return ConversionResult<Tgt>(static_cast<Tgt>(value));
1177 * Checked conversion from floating to floating. The checks are only
1178 * performed when meaningful, e.g. conversion from float to double goes
1181 template <class Tgt, class Src>
1182 typename std::enable_if<
1183 std::is_floating_point<Tgt>::value && std::is_floating_point<Src>::value &&
1184 !std::is_same<Tgt, Src>::value,
1185 ConversionResult<Tgt>>::type
1186 convertTo(const Src& value) {
1188 std::numeric_limits<Tgt>::max() < std::numeric_limits<Src>::max()) {
1189 if (value > std::numeric_limits<Tgt>::max()) {
1190 return ConversionResult<Tgt>(ConversionError::ARITH_POSITIVE_OVERFLOW);
1192 if (value < std::numeric_limits<Tgt>::lowest()) {
1193 return ConversionResult<Tgt>(ConversionError::ARITH_NEGATIVE_OVERFLOW);
1196 return ConversionResult<Tgt>(boost::implicit_cast<Tgt>(value));
1200 * Check if a floating point value can safely be converted to an
1201 * integer value without triggering undefined behaviour.
1203 template <typename Tgt, typename Src>
1204 inline typename std::enable_if<
1205 std::is_floating_point<Src>::value && std::is_integral<Tgt>::value &&
1206 !std::is_same<Tgt, bool>::value,
1208 checkConversion(const Src& value) {
1209 constexpr Src tgtMaxAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::max());
1210 constexpr Src tgtMinAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::min());
1211 if (value >= tgtMaxAsSrc) {
1212 if (value > tgtMaxAsSrc) {
1215 const Src mmax = folly::nextafter(tgtMaxAsSrc, Src());
1216 if (static_cast<Tgt>(value - mmax) >
1217 std::numeric_limits<Tgt>::max() - static_cast<Tgt>(mmax)) {
1220 } else if (std::is_signed<Tgt>::value && value <= tgtMinAsSrc) {
1221 if (value < tgtMinAsSrc) {
1224 const Src mmin = folly::nextafter(tgtMinAsSrc, Src());
1225 if (static_cast<Tgt>(value - mmin) <
1226 std::numeric_limits<Tgt>::min() - static_cast<Tgt>(mmin)) {
1233 // Integers can always safely be converted to floating point values
1234 template <typename Tgt, typename Src>
1235 constexpr typename std::enable_if<
1236 std::is_integral<Src>::value && std::is_floating_point<Tgt>::value,
1238 checkConversion(const Src&) {
1242 // Also, floating point values can always be safely converted to bool
1243 // Per the standard, any floating point value that is not zero will yield true
1244 template <typename Tgt, typename Src>
1245 constexpr typename std::enable_if<
1246 std::is_floating_point<Src>::value && std::is_same<Tgt, bool>::value,
1248 checkConversion(const Src&) {
1253 * Checked conversion from integral to floating point and back. The
1254 * result must be convertible back to the source type without loss of
1255 * precision. This seems Draconian but sometimes is what's needed, and
1256 * complements existing routines nicely. For various rounding
1257 * routines, see <math>.
1259 template <typename Tgt, typename Src>
1260 typename std::enable_if<
1261 (std::is_integral<Src>::value && std::is_floating_point<Tgt>::value) ||
1262 (std::is_floating_point<Src>::value && std::is_integral<Tgt>::value),
1263 ConversionResult<Tgt>>::type
1264 convertTo(const Src& value) {
1265 if (LIKELY(checkConversion<Tgt>(value))) {
1266 Tgt result = static_cast<Tgt>(value);
1267 if (LIKELY(checkConversion<Src>(result))) {
1268 Src witness = static_cast<Src>(result);
1269 if (LIKELY(value == witness)) {
1270 return ConversionResult<Tgt>(result);
1274 return ConversionResult<Tgt>(ConversionError::ARITH_LOSS_OF_PRECISION);
1277 template <typename Tgt, typename Src>
1278 inline std::string errorValue(const Src& value) {
1279 #ifdef FOLLY_HAS_RTTI
1280 return to<std::string>("(", demangle(typeid(Tgt)), ") ", value);
1282 return to<std::string>(value);
1286 template <typename Tgt, typename Src>
1287 using IsArithToArith = std::integral_constant<
1289 !std::is_same<Tgt, Src>::value && !std::is_same<Tgt, bool>::value &&
1290 std::is_arithmetic<Src>::value &&
1291 std::is_arithmetic<Tgt>::value>;
1293 } // namespace detail
1295 template <typename Tgt, typename Src>
1296 typename std::enable_if<
1297 detail::IsArithToArith<
1298 typename detail::WrapperInfo<Tgt>::type, Src>::value, Tgt>::type
1299 to(const Src& value) {
1300 auto res = detail::convertTo<typename detail::WrapperInfo<Tgt>::type>(value);
1301 return detail::wrap<Tgt>(res, [&] {
1302 return detail::errorValue<typename detail::WrapperInfo<Tgt>::type>(value);
1306 /*******************************************************************************
1307 * Custom Conversions
1309 * Any type can be used with folly::to by implementing parseTo. The
1310 * implementation should be provided in the namespace of the type to facilitate
1311 * argument-dependent lookup:
1313 * namespace other_namespace {
1314 * void parseTo(::folly::StringPiece, OtherType&);
1316 ******************************************************************************/
1318 typename std::enable_if<std::is_enum<T>::value>::type
1319 parseTo(StringPiece in, T& out) {
1320 typename std::underlying_type<T>::type tmp;
1322 out = static_cast<T>(tmp);
1325 inline void parseTo(StringPiece in, StringPiece& out) {
1329 inline void parseTo(StringPiece in, std::string& out) {
1331 out.append(in.data(), in.size());
1334 inline void parseTo(StringPiece in, fbstring& out) {
1336 out.append(in.data(), in.size());
1340 * String or StringPiece to target conversion. Accepts leading and trailing
1341 * whitespace, but no non-space trailing characters.
1344 template <class Tgt>
1345 typename std::enable_if<!std::is_same<StringPiece, Tgt>::value, Tgt>::type
1346 to(StringPiece src) {
1348 parseTo(src, result);
1352 template <class Tgt>
1353 Tgt to(StringPiece* src) {
1355 parseTo(src, result);
1359 /*******************************************************************************
1360 * Enum to anything and back
1361 ******************************************************************************/
1363 template <class Tgt, class Src>
1364 typename std::enable_if<
1365 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value, Tgt>::type
1366 to(const Src & value) {
1367 return to<Tgt>(static_cast<typename std::underlying_type<Src>::type>(value));
1370 template <class Tgt, class Src>
1371 typename std::enable_if<
1372 std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value, Tgt>::type
1373 to(const Src & value) {
1374 return static_cast<Tgt>(to<typename std::underlying_type<Tgt>::type>(value));
1377 } // namespace folly