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 * Everything implicitly convertible to const char* gets appended.
414 template <class Tgt, class Src>
415 typename std::enable_if<
416 std::is_convertible<Src, const char*>::value
417 && IsSomeString<Tgt>::value>::type
418 toAppend(Src value, Tgt * result) {
419 // Treat null pointers like an empty string, as in:
420 // operator<<(std::ostream&, const char*).
421 const char* c = value;
423 result->append(value);
428 typename std::enable_if<std::is_convertible<Src, const char*>::value, size_t>::
430 estimateSpaceNeeded(Src value) {
431 const char *c = value;
433 return folly::StringPiece(value).size();
439 typename std::enable_if<
440 (std::is_convertible<Src, folly::StringPiece>::value ||
441 IsSomeString<Src>::value) &&
442 !std::is_convertible<Src, const char*>::value,
444 estimateSpaceNeeded(Src value) {
445 return folly::StringPiece(value).size();
449 inline size_t estimateSpaceNeeded(std::nullptr_t /* value */) {
454 typename std::enable_if<
455 std::is_pointer<Src>::value &&
456 IsSomeString<std::remove_pointer<Src>>::value,
458 estimateSpaceNeeded(Src value) {
459 return value->size();
463 * Strings get appended, too.
465 template <class Tgt, class Src>
466 typename std::enable_if<
467 IsSomeString<Src>::value && IsSomeString<Tgt>::value>::type
468 toAppend(const Src& value, Tgt * result) {
469 result->append(value);
473 * and StringPiece objects too
476 typename std::enable_if<
477 IsSomeString<Tgt>::value>::type
478 toAppend(StringPiece value, Tgt * result) {
479 result->append(value.data(), value.size());
483 * There's no implicit conversion from fbstring to other string types,
484 * so make a specialization.
487 typename std::enable_if<
488 IsSomeString<Tgt>::value>::type
489 toAppend(const fbstring& value, Tgt * result) {
490 result->append(value.data(), value.size());
493 #if FOLLY_HAVE_INT128_T
495 * Special handling for 128 bit integers.
500 toAppend(__int128 value, Tgt * result) {
501 typedef unsigned __int128 Usrc;
502 char buffer[detail::digitsEnough<unsigned __int128>() + 1];
506 p = detail::unsafeTelescope128(buffer, sizeof(buffer), -Usrc(value));
509 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
512 result->append(buffer + p, buffer + sizeof(buffer));
517 toAppend(unsigned __int128 value, Tgt * result) {
518 char buffer[detail::digitsEnough<unsigned __int128>()];
521 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
523 result->append(buffer + p, buffer + sizeof(buffer));
527 constexpr typename std::enable_if<
528 std::is_same<T, __int128>::value,
530 estimateSpaceNeeded(T) {
531 return detail::digitsEnough<__int128>();
535 constexpr typename std::enable_if<
536 std::is_same<T, unsigned __int128>::value,
538 estimateSpaceNeeded(T) {
539 return detail::digitsEnough<unsigned __int128>();
545 * int32_t and int64_t to string (by appending) go through here. The
546 * result is APPENDED to a preexisting string passed as the second
547 * parameter. This should be efficient with fbstring because fbstring
548 * incurs no dynamic allocation below 23 bytes and no number has more
549 * than 22 bytes in its textual representation (20 for digits, one for
550 * sign, one for the terminating 0).
552 template <class Tgt, class Src>
553 typename std::enable_if<
554 std::is_integral<Src>::value && std::is_signed<Src>::value &&
555 IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
556 toAppend(Src value, Tgt * result) {
559 result->push_back('-');
560 using u = std::make_signed<size_t>::type;
563 uint64ToBufferUnsafe(
564 static_cast<size_t>(-static_cast<u>(value)), buffer));
566 result->append(buffer, uint64ToBufferUnsafe(uint64_t(value), buffer));
571 typename std::enable_if<
572 std::is_integral<Src>::value && std::is_signed<Src>::value
573 && sizeof(Src) >= 4 && sizeof(Src) < 16,
575 estimateSpaceNeeded(Src value) {
577 // When "value" is the smallest negative, negating it would evoke
578 // undefined behavior, so, instead of writing "-value" below, we write
579 // "~static_cast<uint64_t>(value) + 1"
580 return 1 + digits10(~static_cast<uint64_t>(value) + 1);
583 return digits10(static_cast<uint64_t>(value));
587 * As above, but for uint32_t and uint64_t.
589 template <class Tgt, class Src>
590 typename std::enable_if<
591 std::is_integral<Src>::value && !std::is_signed<Src>::value
592 && IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
593 toAppend(Src value, Tgt * result) {
595 result->append(buffer, uint64ToBufferUnsafe(value, buffer));
599 typename std::enable_if<
600 std::is_integral<Src>::value && !std::is_signed<Src>::value
601 && sizeof(Src) >= 4 && sizeof(Src) < 16,
603 estimateSpaceNeeded(Src value) {
604 return digits10(value);
608 * All small signed and unsigned integers to string go through 32-bit
609 * types int32_t and uint32_t, respectively.
611 template <class Tgt, class Src>
612 typename std::enable_if<
613 std::is_integral<Src>::value
614 && IsSomeString<Tgt>::value && sizeof(Src) < 4>::type
615 toAppend(Src value, Tgt * result) {
617 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
619 toAppend<Tgt>(static_cast<Intermediate>(value), result);
623 typename std::enable_if<
624 std::is_integral<Src>::value
626 && !std::is_same<Src, char>::value,
628 estimateSpaceNeeded(Src value) {
630 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
632 return estimateSpaceNeeded(static_cast<Intermediate>(value));
636 * Enumerated values get appended as integers.
638 template <class Tgt, class Src>
639 typename std::enable_if<
640 std::is_enum<Src>::value && IsSomeString<Tgt>::value>::type
641 toAppend(Src value, Tgt * result) {
643 static_cast<typename std::underlying_type<Src>::type>(value), result);
647 typename std::enable_if<
648 std::is_enum<Src>::value, size_t>::type
649 estimateSpaceNeeded(Src value) {
650 return estimateSpaceNeeded(
651 static_cast<typename std::underlying_type<Src>::type>(value));
654 /*******************************************************************************
655 * Conversions from floating-point types to string types.
656 ******************************************************************************/
659 constexpr int kConvMaxDecimalInShortestLow = -6;
660 constexpr int kConvMaxDecimalInShortestHigh = 21;
663 /** Wrapper around DoubleToStringConverter **/
664 template <class Tgt, class Src>
665 typename std::enable_if<
666 std::is_floating_point<Src>::value
667 && IsSomeString<Tgt>::value>::type
671 double_conversion::DoubleToStringConverter::DtoaMode mode,
672 unsigned int numDigits) {
673 using namespace double_conversion;
674 DoubleToStringConverter
675 conv(DoubleToStringConverter::NO_FLAGS,
676 "Infinity", "NaN", 'E',
677 detail::kConvMaxDecimalInShortestLow,
678 detail::kConvMaxDecimalInShortestHigh,
679 6, // max leading padding zeros
680 1); // max trailing padding zeros
682 StringBuilder builder(buffer, sizeof(buffer));
684 case DoubleToStringConverter::SHORTEST:
685 conv.ToShortest(value, &builder);
687 case DoubleToStringConverter::FIXED:
688 conv.ToFixed(value, int(numDigits), &builder);
691 CHECK(mode == DoubleToStringConverter::PRECISION);
692 conv.ToPrecision(value, int(numDigits), &builder);
695 const size_t length = size_t(builder.position());
697 result->append(buffer, length);
701 * As above, but for floating point
703 template <class Tgt, class Src>
704 typename std::enable_if<
705 std::is_floating_point<Src>::value
706 && IsSomeString<Tgt>::value>::type
707 toAppend(Src value, Tgt * result) {
709 value, result, double_conversion::DoubleToStringConverter::SHORTEST, 0);
713 * Upper bound of the length of the output from
714 * DoubleToStringConverter::ToShortest(double, StringBuilder*),
715 * as used in toAppend(double, string*).
718 typename std::enable_if<
719 std::is_floating_point<Src>::value, size_t>::type
720 estimateSpaceNeeded(Src value) {
721 // kBase10MaximalLength is 17. We add 1 for decimal point,
722 // e.g. 10.0/9 is 17 digits and 18 characters, including the decimal point.
723 constexpr int kMaxMantissaSpace =
724 double_conversion::DoubleToStringConverter::kBase10MaximalLength + 1;
725 // strlen("E-") + digits10(numeric_limits<double>::max_exponent10)
726 constexpr int kMaxExponentSpace = 2 + 3;
727 static const int kMaxPositiveSpace = std::max({
728 // E.g. 1.1111111111111111E-100.
729 kMaxMantissaSpace + kMaxExponentSpace,
730 // E.g. 0.000001.1111111111111111, if kConvMaxDecimalInShortestLow is -6.
731 kMaxMantissaSpace - detail::kConvMaxDecimalInShortestLow,
732 // If kConvMaxDecimalInShortestHigh is 21, then 1e21 is the smallest
733 // number > 1 which ToShortest outputs in exponential notation,
734 // so 21 is the longest non-exponential number > 1.
735 detail::kConvMaxDecimalInShortestHigh
739 (value < 0 ? 1 : 0)); // +1 for minus sign, if negative
743 * This can be specialized, together with adding specialization
744 * for estimateSpaceNeed for your type, so that we allocate
745 * as much as you need instead of the default
748 struct HasLengthEstimator : std::false_type {};
751 constexpr typename std::enable_if<
752 !std::is_fundamental<Src>::value
753 #if FOLLY_HAVE_INT128_T
754 // On OSX 10.10, is_fundamental<__int128> is false :-O
755 && !std::is_same<__int128, Src>::value
756 && !std::is_same<unsigned __int128, Src>::value
758 && !IsSomeString<Src>::value
759 && !std::is_convertible<Src, const char*>::value
760 && !std::is_convertible<Src, StringPiece>::value
761 && !std::is_enum<Src>::value
762 && !HasLengthEstimator<Src>::value,
764 estimateSpaceNeeded(const Src&) {
765 return sizeof(Src) + 1; // dumbest best effort ever?
771 typename std::enable_if<IsSomeString<Tgt>::value, size_t>::type
772 estimateSpaceToReserve(size_t sofar, Tgt*) {
776 template <class T, class... Ts>
777 size_t estimateSpaceToReserve(size_t sofar, const T& v, const Ts&... vs) {
778 return estimateSpaceToReserve(sofar + estimateSpaceNeeded(v), vs...);
782 void reserveInTarget(const Ts&...vs) {
783 getLastElement(vs...)->reserve(estimateSpaceToReserve(0, vs...));
786 template<class Delimiter, class...Ts>
787 void reserveInTargetDelim(const Delimiter& d, const Ts&...vs) {
788 static_assert(sizeof...(vs) >= 2, "Needs at least 2 args");
789 size_t fordelim = (sizeof...(vs) - 2) *
790 estimateSpaceToReserve(0, d, static_cast<std::string*>(nullptr));
791 getLastElement(vs...)->reserve(estimateSpaceToReserve(fordelim, vs...));
795 * Variadic base case: append one element
797 template <class T, class Tgt>
798 typename std::enable_if<
799 IsSomeString<typename std::remove_pointer<Tgt>::type>
801 toAppendStrImpl(const T& v, Tgt result) {
805 template <class T, class... Ts>
806 typename std::enable_if<
807 sizeof...(Ts) >= 2 &&
808 IsSomeString<typename std::remove_pointer<
809 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
810 toAppendStrImpl(const T& v, const Ts&... vs) {
811 toAppend(v, getLastElement(vs...));
812 toAppendStrImpl(vs...);
815 template <class Delimiter, class T, class Tgt>
816 typename std::enable_if<
817 IsSomeString<typename std::remove_pointer<Tgt>::type>::value>::type
818 toAppendDelimStrImpl(const Delimiter& /* delim */, const T& v, Tgt result) {
822 template <class Delimiter, class T, class... Ts>
823 typename std::enable_if<
824 sizeof...(Ts) >= 2 &&
825 IsSomeString<typename std::remove_pointer<
826 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
827 toAppendDelimStrImpl(const Delimiter& delim, const T& v, const Ts&... vs) {
828 // we are really careful here, calling toAppend with just one element does
829 // not try to estimate space needed (as we already did that). If we call
830 // toAppend(v, delim, ....) we would do unnecesary size calculation
831 toAppend(v, detail::getLastElement(vs...));
832 toAppend(delim, detail::getLastElement(vs...));
833 toAppendDelimStrImpl(delim, vs...);
839 * Variadic conversion to string. Appends each element in turn.
840 * If we have two or more things to append, we it will not reserve
841 * the space for them and will depend on strings exponential growth.
842 * If you just append once consider using toAppendFit which reserves
843 * the space needed (but does not have exponential as a result).
845 * Custom implementations of toAppend() can be provided in the same namespace as
846 * the type to customize printing. estimateSpaceNeed() may also be provided to
847 * avoid reallocations in toAppendFit():
849 * namespace other_namespace {
851 * template <class String>
852 * void toAppend(const OtherType&, String* out);
855 * size_t estimateSpaceNeeded(const OtherType&);
859 template <class... Ts>
860 typename std::enable_if<
861 sizeof...(Ts) >= 3 &&
862 IsSomeString<typename std::remove_pointer<
863 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
864 toAppend(const Ts&... vs) {
865 ::folly::detail::toAppendStrImpl(vs...);
869 // Special case pid_t on MSVC, because it's a void* rather than an
870 // integral type. We can't do a global special case because this is already
871 // dangerous enough (as most pointers will implicitly convert to a void*)
872 // just doing it for MSVC.
874 void toAppend(const pid_t a, Tgt* res) {
875 toAppend(uint64_t(a), res);
880 * Special version of the call that preallocates exaclty as much memory
881 * as need for arguments to be stored in target. This means we are
882 * not doing exponential growth when we append. If you are using it
883 * in a loop you are aiming at your foot with a big perf-destroying
885 * On the other hand if you are appending to a string once, this
886 * will probably save a few calls to malloc.
888 template <class... Ts>
889 typename std::enable_if<IsSomeString<typename std::remove_pointer<
890 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
891 toAppendFit(const Ts&... vs) {
892 ::folly::detail::reserveInTarget(vs...);
897 void toAppendFit(const Ts&) {}
900 * Variadic base case: do nothing.
903 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppend(
904 Tgt* /* result */) {}
907 * Variadic base case: do nothing.
909 template <class Delimiter, class Tgt>
910 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
911 const Delimiter& /* delim */, Tgt* /* result */) {}
914 * 1 element: same as toAppend.
916 template <class Delimiter, class T, class Tgt>
917 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
918 const Delimiter& /* delim */, const T& v, Tgt* tgt) {
923 * Append to string with a delimiter in between elements. Check out
924 * comments for toAppend for details about memory allocation.
926 template <class Delimiter, class... Ts>
927 typename std::enable_if<
928 sizeof...(Ts) >= 3 &&
929 IsSomeString<typename std::remove_pointer<
930 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
931 toAppendDelim(const Delimiter& delim, const Ts&... vs) {
932 detail::toAppendDelimStrImpl(delim, vs...);
936 * Detail in comment for toAppendFit
938 template <class Delimiter, class... Ts>
939 typename std::enable_if<IsSomeString<typename std::remove_pointer<
940 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
941 toAppendDelimFit(const Delimiter& delim, const Ts&... vs) {
942 detail::reserveInTargetDelim(delim, vs...);
943 toAppendDelim(delim, vs...);
946 template <class De, class Ts>
947 void toAppendDelimFit(const De&, const Ts&) {}
950 * to<SomeString>(v1, v2, ...) uses toAppend() (see below) as back-end
953 template <class Tgt, class... Ts>
954 typename std::enable_if<
955 IsSomeString<Tgt>::value &&
956 (sizeof...(Ts) != 1 ||
957 !std::is_same<Tgt, typename detail::LastElement<const Ts&...>::type>::
960 to(const Ts&... vs) {
962 toAppendFit(vs..., &result);
967 * Special version of to<SomeString> for floating point. When calling
968 * folly::to<SomeString>(double), generic implementation above will
969 * firstly reserve 24 (or 25 when negative value) bytes. This will
970 * introduce a malloc call for most mainstream string implementations.
972 * But for most cases, a floating point doesn't need 24 (or 25) bytes to
973 * be converted as a string.
975 * This special version will not do string reserve.
977 template <class Tgt, class Src>
978 typename std::enable_if<
979 IsSomeString<Tgt>::value && std::is_floating_point<Src>::value,
983 toAppend(value, &result);
988 * toDelim<SomeString>(SomeString str) returns itself.
990 template <class Tgt, class Delim, class Src>
991 typename std::enable_if<IsSomeString<Tgt>::value &&
992 std::is_same<Tgt, Src>::value,
994 toDelim(const Delim& /* delim */, const Src& value) {
999 * toDelim<SomeString>(delim, v1, v2, ...) uses toAppendDelim() as
1000 * back-end for all types.
1002 template <class Tgt, class Delim, class... Ts>
1003 typename std::enable_if<
1004 IsSomeString<Tgt>::value &&
1005 (sizeof...(Ts) != 1 ||
1006 !std::is_same<Tgt, typename detail::LastElement<const Ts&...>::type>::
1009 toDelim(const Delim& delim, const Ts&... vs) {
1011 toAppendDelimFit(delim, vs..., &result);
1015 /*******************************************************************************
1016 * Conversions from string types to integral types.
1017 ******************************************************************************/
1021 Expected<bool, ConversionCode> str_to_bool(StringPiece* src) noexcept;
1023 template <typename T>
1024 Expected<T, ConversionCode> str_to_floating(StringPiece* src) noexcept;
1026 extern template Expected<float, ConversionCode> str_to_floating<float>(
1027 StringPiece* src) noexcept;
1028 extern template Expected<double, ConversionCode> str_to_floating<double>(
1029 StringPiece* src) noexcept;
1031 template <class Tgt>
1032 Expected<Tgt, ConversionCode> digits_to(const char* b, const char* e) noexcept;
1034 extern template Expected<char, ConversionCode> digits_to<char>(
1036 const char*) noexcept;
1037 extern template Expected<signed char, ConversionCode> digits_to<signed char>(
1039 const char*) noexcept;
1040 extern template Expected<unsigned char, ConversionCode>
1041 digits_to<unsigned char>(const char*, const char*) noexcept;
1043 extern template Expected<short, ConversionCode> digits_to<short>(
1045 const char*) noexcept;
1046 extern template Expected<unsigned short, ConversionCode>
1047 digits_to<unsigned short>(const char*, const char*) noexcept;
1049 extern template Expected<int, ConversionCode> digits_to<int>(
1051 const char*) noexcept;
1052 extern template Expected<unsigned int, ConversionCode> digits_to<unsigned int>(
1054 const char*) noexcept;
1056 extern template Expected<long, ConversionCode> digits_to<long>(
1058 const char*) noexcept;
1059 extern template Expected<unsigned long, ConversionCode>
1060 digits_to<unsigned long>(const char*, const char*) noexcept;
1062 extern template Expected<long long, ConversionCode> digits_to<long long>(
1064 const char*) noexcept;
1065 extern template Expected<unsigned long long, ConversionCode>
1066 digits_to<unsigned long long>(const char*, const char*) noexcept;
1068 #if FOLLY_HAVE_INT128_T
1069 extern template Expected<__int128, ConversionCode> digits_to<__int128>(
1071 const char*) noexcept;
1072 extern template Expected<unsigned __int128, ConversionCode>
1073 digits_to<unsigned __int128>(const char*, const char*) noexcept;
1077 Expected<T, ConversionCode> str_to_integral(StringPiece* src) noexcept;
1079 extern template Expected<char, ConversionCode> str_to_integral<char>(
1080 StringPiece* src) noexcept;
1081 extern template Expected<signed char, ConversionCode>
1082 str_to_integral<signed char>(StringPiece* src) noexcept;
1083 extern template Expected<unsigned char, ConversionCode>
1084 str_to_integral<unsigned char>(StringPiece* src) noexcept;
1086 extern template Expected<short, ConversionCode> str_to_integral<short>(
1087 StringPiece* src) noexcept;
1088 extern template Expected<unsigned short, ConversionCode>
1089 str_to_integral<unsigned short>(StringPiece* src) noexcept;
1091 extern template Expected<int, ConversionCode> str_to_integral<int>(
1092 StringPiece* src) noexcept;
1093 extern template Expected<unsigned int, ConversionCode>
1094 str_to_integral<unsigned int>(StringPiece* src) noexcept;
1096 extern template Expected<long, ConversionCode> str_to_integral<long>(
1097 StringPiece* src) noexcept;
1098 extern template Expected<unsigned long, ConversionCode>
1099 str_to_integral<unsigned long>(StringPiece* src) noexcept;
1101 extern template Expected<long long, ConversionCode> str_to_integral<long long>(
1102 StringPiece* src) noexcept;
1103 extern template Expected<unsigned long long, ConversionCode>
1104 str_to_integral<unsigned long long>(StringPiece* src) noexcept;
1106 #if FOLLY_HAVE_INT128_T
1107 extern template Expected<__int128, ConversionCode> str_to_integral<__int128>(
1108 StringPiece* src) noexcept;
1109 extern template Expected<unsigned __int128, ConversionCode>
1110 str_to_integral<unsigned __int128>(StringPiece* src) noexcept;
1113 template <typename T>
1115 enable_if<std::is_same<T, bool>::value, Expected<T, ConversionCode>>::type
1116 convertTo(StringPiece* src) noexcept {
1117 return str_to_bool(src);
1120 template <typename T>
1121 typename std::enable_if<
1122 std::is_floating_point<T>::value,
1123 Expected<T, ConversionCode>>::type
1124 convertTo(StringPiece* src) noexcept {
1125 return str_to_floating<T>(src);
1128 template <typename T>
1129 typename std::enable_if<
1130 std::is_integral<T>::value && !std::is_same<T, bool>::value,
1131 Expected<T, ConversionCode>>::type
1132 convertTo(StringPiece* src) noexcept {
1133 return str_to_integral<T>(src);
1136 } // namespace detail
1139 * String represented as a pair of pointers to char to unsigned
1140 * integrals. Assumes NO whitespace before or after.
1142 template <typename Tgt>
1143 typename std::enable_if<
1144 std::is_integral<Tgt>::value && !std::is_same<Tgt, bool>::value,
1145 Expected<Tgt, ConversionCode>>::type
1146 tryTo(const char* b, const char* e) {
1147 return detail::digits_to<Tgt>(b, e);
1150 template <typename Tgt>
1151 typename std::enable_if<
1152 std::is_integral<Tgt>::value && !std::is_same<Tgt, bool>::value,
1154 to(const char* b, const char* e) {
1155 return tryTo<Tgt>(b, e).thenOrThrow(
1156 [](Tgt res) { return res; },
1157 [=](ConversionCode code) {
1158 return makeConversionError(code, StringPiece(b, e));
1162 /*******************************************************************************
1163 * Conversions from string types to arithmetic types.
1164 ******************************************************************************/
1167 * Parsing strings to numeric types.
1169 template <typename Tgt>
1170 FOLLY_WARN_UNUSED_RESULT inline typename std::enable_if<
1171 std::is_arithmetic<Tgt>::value,
1172 Expected<StringPiece, ConversionCode>>::type
1173 parseTo(StringPiece src, Tgt& out) {
1174 return detail::convertTo<Tgt>(&src).then(
1175 [&](Tgt res) { return void(out = res), src; });
1178 /*******************************************************************************
1179 * Integral / Floating Point to integral / Floating Point
1180 ******************************************************************************/
1185 * Bool to integral/float doesn't need any special checks, and this
1186 * overload means we aren't trying to see if a bool is less than
1189 template <class Tgt>
1190 typename std::enable_if<
1191 !std::is_same<Tgt, bool>::value &&
1192 (std::is_integral<Tgt>::value || std::is_floating_point<Tgt>::value),
1193 Expected<Tgt, ConversionCode>>::type
1194 convertTo(const bool& value) noexcept {
1195 return static_cast<Tgt>(value ? 1 : 0);
1199 * Checked conversion from integral to integral. The checks are only
1200 * performed when meaningful, e.g. conversion from int to long goes
1203 template <class Tgt, class Src>
1204 typename std::enable_if<
1205 std::is_integral<Src>::value && !std::is_same<Tgt, Src>::value &&
1206 !std::is_same<Tgt, bool>::value &&
1207 std::is_integral<Tgt>::value,
1208 Expected<Tgt, ConversionCode>>::type
1209 convertTo(const Src& value) noexcept {
1211 folly::_t<std::make_unsigned<Tgt>>(std::numeric_limits<Tgt>::max()) <
1212 folly::_t<std::make_unsigned<Src>>(std::numeric_limits<Src>::max())) {
1213 if (greater_than<Tgt, std::numeric_limits<Tgt>::max()>(value)) {
1214 return makeUnexpected(ConversionCode::ARITH_POSITIVE_OVERFLOW);
1218 std::is_signed<Src>::value &&
1219 (!std::is_signed<Tgt>::value || sizeof(Src) > sizeof(Tgt))) {
1220 if (less_than<Tgt, std::numeric_limits<Tgt>::min()>(value)) {
1221 return makeUnexpected(ConversionCode::ARITH_NEGATIVE_OVERFLOW);
1224 return static_cast<Tgt>(value);
1228 * Checked conversion from floating to floating. The checks are only
1229 * performed when meaningful, e.g. conversion from float to double goes
1232 template <class Tgt, class Src>
1233 typename std::enable_if<
1234 std::is_floating_point<Tgt>::value && std::is_floating_point<Src>::value &&
1235 !std::is_same<Tgt, Src>::value,
1236 Expected<Tgt, ConversionCode>>::type
1237 convertTo(const Src& value) noexcept {
1239 std::numeric_limits<Tgt>::max() < std::numeric_limits<Src>::max()) {
1240 if (value > std::numeric_limits<Tgt>::max()) {
1241 return makeUnexpected(ConversionCode::ARITH_POSITIVE_OVERFLOW);
1243 if (value < std::numeric_limits<Tgt>::lowest()) {
1244 return makeUnexpected(ConversionCode::ARITH_NEGATIVE_OVERFLOW);
1247 return static_cast<Tgt>(value);
1251 * Check if a floating point value can safely be converted to an
1252 * integer value without triggering undefined behaviour.
1254 template <typename Tgt, typename Src>
1255 inline typename std::enable_if<
1256 std::is_floating_point<Src>::value && std::is_integral<Tgt>::value &&
1257 !std::is_same<Tgt, bool>::value,
1259 checkConversion(const Src& value) {
1260 constexpr Src tgtMaxAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::max());
1261 constexpr Src tgtMinAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::min());
1262 if (value >= tgtMaxAsSrc) {
1263 if (value > tgtMaxAsSrc) {
1266 const Src mmax = folly::nextafter(tgtMaxAsSrc, Src());
1267 if (static_cast<Tgt>(value - mmax) >
1268 std::numeric_limits<Tgt>::max() - static_cast<Tgt>(mmax)) {
1271 } else if (std::is_signed<Tgt>::value && value <= tgtMinAsSrc) {
1272 if (value < tgtMinAsSrc) {
1275 const Src mmin = folly::nextafter(tgtMinAsSrc, Src());
1276 if (static_cast<Tgt>(value - mmin) <
1277 std::numeric_limits<Tgt>::min() - static_cast<Tgt>(mmin)) {
1284 // Integers can always safely be converted to floating point values
1285 template <typename Tgt, typename Src>
1286 constexpr typename std::enable_if<
1287 std::is_integral<Src>::value && std::is_floating_point<Tgt>::value,
1289 checkConversion(const Src&) {
1293 // Also, floating point values can always be safely converted to bool
1294 // Per the standard, any floating point value that is not zero will yield true
1295 template <typename Tgt, typename Src>
1296 constexpr typename std::enable_if<
1297 std::is_floating_point<Src>::value && std::is_same<Tgt, bool>::value,
1299 checkConversion(const Src&) {
1304 * Checked conversion from integral to floating point and back. The
1305 * result must be convertible back to the source type without loss of
1306 * precision. This seems Draconian but sometimes is what's needed, and
1307 * complements existing routines nicely. For various rounding
1308 * routines, see <math>.
1310 template <typename Tgt, typename Src>
1311 typename std::enable_if<
1312 (std::is_integral<Src>::value && std::is_floating_point<Tgt>::value) ||
1313 (std::is_floating_point<Src>::value && std::is_integral<Tgt>::value),
1314 Expected<Tgt, ConversionCode>>::type
1315 convertTo(const Src& value) noexcept {
1316 if (LIKELY(checkConversion<Tgt>(value))) {
1317 Tgt result = static_cast<Tgt>(value);
1318 if (LIKELY(checkConversion<Src>(result))) {
1319 Src witness = static_cast<Src>(result);
1320 if (LIKELY(value == witness)) {
1325 return makeUnexpected(ConversionCode::ARITH_LOSS_OF_PRECISION);
1328 template <typename Tgt, typename Src>
1329 inline std::string errorValue(const Src& value) {
1330 #ifdef FOLLY_HAS_RTTI
1331 return to<std::string>("(", demangle(typeid(Tgt)), ") ", value);
1333 return to<std::string>(value);
1337 template <typename Tgt, typename Src>
1338 using IsArithToArith = std::integral_constant<
1340 !std::is_same<Tgt, Src>::value && !std::is_same<Tgt, bool>::value &&
1341 std::is_arithmetic<Src>::value &&
1342 std::is_arithmetic<Tgt>::value>;
1344 } // namespace detail
1346 template <typename Tgt, typename Src>
1347 typename std::enable_if<
1348 detail::IsArithToArith<Tgt, Src>::value,
1349 Expected<Tgt, ConversionCode>>::type
1350 tryTo(const Src& value) noexcept {
1351 return detail::convertTo<Tgt>(value);
1354 template <typename Tgt, typename Src>
1355 typename std::enable_if<detail::IsArithToArith<Tgt, Src>::value, Tgt>::type to(
1357 return tryTo<Tgt>(value).thenOrThrow(
1358 [](Tgt res) { return res; },
1359 [&](ConversionCode e) {
1360 return makeConversionError(e, detail::errorValue<Tgt>(value));
1364 /*******************************************************************************
1365 * Custom Conversions
1367 * Any type can be used with folly::to by implementing parseTo. The
1368 * implementation should be provided in the namespace of the type to facilitate
1369 * argument-dependent lookup:
1371 * namespace other_namespace {
1372 * ::folly::Expected<::folly::StringPiece, SomeErrorCode>
1373 * parseTo(::folly::StringPiece, OtherType&) noexcept;
1375 ******************************************************************************/
1377 FOLLY_WARN_UNUSED_RESULT typename std::enable_if<
1378 std::is_enum<T>::value,
1379 Expected<StringPiece, ConversionCode>>::type
1380 parseTo(StringPiece in, T& out) noexcept {
1381 typename std::underlying_type<T>::type tmp{};
1382 auto restOrError = parseTo(in, tmp);
1383 out = static_cast<T>(tmp); // Harmless if parseTo fails
1387 FOLLY_WARN_UNUSED_RESULT
1388 inline Expected<StringPiece, ConversionCode> parseTo(
1390 StringPiece& out) noexcept {
1392 return StringPiece{in.end(), in.end()};
1395 FOLLY_WARN_UNUSED_RESULT
1396 inline Expected<StringPiece, ConversionCode> parseTo(
1400 out.append(in.data(), in.size()); // TODO try/catch?
1401 return StringPiece{in.end(), in.end()};
1404 FOLLY_WARN_UNUSED_RESULT
1405 inline Expected<StringPiece, ConversionCode> parseTo(
1409 out.append(in.data(), in.size()); // TODO try/catch?
1410 return StringPiece{in.end(), in.end()};
1414 template <typename Tgt>
1415 using ParseToResult = decltype(parseTo(StringPiece{}, std::declval<Tgt&>()));
1417 struct CheckTrailingSpace {
1418 Expected<Unit, ConversionCode> operator()(StringPiece sp) const {
1419 auto e = enforceWhitespaceErr(sp);
1420 if (UNLIKELY(e != ConversionCode::SUCCESS))
1421 return makeUnexpected(e);
1426 template <class Error>
1429 constexpr Expected<Unit, Error> operator()(T&&) const {
1434 // Older versions of the parseTo customization point threw on error and
1435 // returned void. Handle that.
1436 template <class Tgt>
1437 inline typename std::enable_if<
1438 std::is_void<ParseToResult<Tgt>>::value,
1439 Expected<StringPiece, ConversionCode>>::type
1440 parseToWrap(StringPiece sp, Tgt& out) {
1442 return StringPiece(sp.end(), sp.end());
1445 template <class Tgt>
1446 inline typename std::enable_if<
1447 !std::is_void<ParseToResult<Tgt>>::value,
1448 ParseToResult<Tgt>>::type
1449 parseToWrap(StringPiece sp, Tgt& out) {
1450 return parseTo(sp, out);
1453 template <typename Tgt>
1454 using ParseToError = ExpectedErrorType<decltype(
1455 detail::parseToWrap(StringPiece{}, std::declval<Tgt&>()))>;
1457 } // namespace detail
1460 * String or StringPiece to target conversion. Accepts leading and trailing
1461 * whitespace, but no non-space trailing characters.
1464 template <class Tgt>
1465 inline typename std::enable_if<
1466 !std::is_same<StringPiece, Tgt>::value,
1467 Expected<Tgt, detail::ParseToError<Tgt>>>::type
1468 tryTo(StringPiece src) {
1470 using Error = detail::ParseToError<Tgt>;
1471 using Check = typename std::conditional<
1472 std::is_arithmetic<Tgt>::value,
1473 detail::CheckTrailingSpace,
1474 detail::ReturnUnit<Error>>::type;
1475 return parseTo(src, result).then(Check(), [&](Unit) {
1476 return std::move(result);
1480 template <class Tgt>
1482 typename std::enable_if<!std::is_same<StringPiece, Tgt>::value, Tgt>::type
1483 to(StringPiece src) {
1485 using Error = detail::ParseToError<Tgt>;
1486 using Check = typename std::conditional<
1487 std::is_arithmetic<Tgt>::value,
1488 detail::CheckTrailingSpace,
1489 detail::ReturnUnit<Error>>::type;
1490 auto tmp = detail::parseToWrap(src, result);
1492 .thenOrThrow(Check(), [&](Error e) { throw makeConversionError(e, src); })
1494 [&](Unit) { return std::move(result); },
1495 [&](Error e) { throw makeConversionError(e, tmp.value()); });
1499 * tryTo/to that take the strings by pointer so the caller gets information
1500 * about how much of the string was consumed by the conversion. These do not
1501 * check for trailing whitepsace.
1503 template <class Tgt>
1504 Expected<Tgt, detail::ParseToError<Tgt>> tryTo(StringPiece* src) {
1506 return parseTo(*src, result).then([&, src](StringPiece sp) -> Tgt {
1508 return std::move(result);
1512 template <class Tgt>
1513 Tgt to(StringPiece* src) {
1515 using Error = detail::ParseToError<Tgt>;
1516 return parseTo(*src, result)
1518 [&, src](StringPiece sp) -> Tgt {
1520 return std::move(result);
1522 [=](Error e) { return makeConversionError(e, *src); });
1525 /*******************************************************************************
1526 * Enum to anything and back
1527 ******************************************************************************/
1529 template <class Tgt, class Src>
1530 typename std::enable_if<
1531 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value,
1532 Expected<Tgt, ConversionCode>>::type
1533 tryTo(const Src& value) {
1534 using I = typename std::underlying_type<Src>::type;
1535 return tryTo<Tgt>(static_cast<I>(value));
1538 template <class Tgt, class Src>
1539 typename std::enable_if<
1540 std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value,
1542 tryTo(const Src& value) {
1543 using I = typename std::underlying_type<Tgt>::type;
1544 return tryTo<I>(value).then([](I i) { return static_cast<Tgt>(i); });
1547 template <class Tgt, class Src>
1548 typename std::enable_if<
1549 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value,
1551 to(const Src& value) {
1552 return to<Tgt>(static_cast<typename std::underlying_type<Src>::type>(value));
1555 template <class Tgt, class Src>
1556 typename std::enable_if<
1557 std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value, Tgt>::type
1558 to(const Src & value) {
1559 return static_cast<Tgt>(to<typename std::underlying_type<Tgt>::type>(value));
1562 } // namespace folly