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);
136 } // namespace detail
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;
286 } // namespace detail
290 * Returns the number of digits in the base 10 representation of an
291 * uint64_t. Useful for preallocating buffers and such. It's also used
292 * internally, see below. Measurements suggest that defining a
293 * separate overload for 32-bit integers is not worthwhile.
296 inline uint32_t digits10(uint64_t v) {
299 // For this arch we can get a little help from specialized CPU instructions
300 // which can count leading zeroes; 64 minus that is appx. log (base 2).
301 // Use that to approximate base-10 digits (log_10) and then adjust if needed.
303 // 10^i, defined for i 0 through 19.
304 // This is 20 * 8 == 160 bytes, which fits neatly into 5 cache lines
305 // (assuming a cache line size of 64).
306 static const uint64_t powersOf10[20] FOLLY_ALIGNED(64) = {
326 10000000000000000000UL,
329 // "count leading zeroes" operation not valid; for 0; special case this.
334 // bits is in the ballpark of log_2(v).
335 const uint8_t leadingZeroes = __builtin_clzll(v);
336 const auto bits = 63 - leadingZeroes;
338 // approximate log_10(v) == log_10(2) * bits.
339 // Integer magic below: 77/256 is appx. 0.3010 (log_10(2)).
340 // The +1 is to make this the ceiling of the log_10 estimate.
341 const uint32_t minLength = 1 + ((bits * 77) >> 8);
343 // return that log_10 lower bound, plus adjust if input >= 10^(that bound)
344 // in case there's a small error and we misjudged length.
345 return minLength + (uint32_t) (UNLIKELY (v >= powersOf10[minLength]));
351 if (LIKELY(v < 10)) return result;
352 if (LIKELY(v < 100)) return result + 1;
353 if (LIKELY(v < 1000)) return result + 2;
354 if (LIKELY(v < 10000)) return result + 3;
355 // Skip ahead by 4 orders of magnitude
364 * Copies the ASCII base 10 representation of v into buffer and
365 * returns the number of bytes written. Does NOT append a \0. Assumes
366 * the buffer points to digits10(v) bytes of valid memory. Note that
367 * uint64 needs at most 20 bytes, uint32_t needs at most 10 bytes,
368 * uint16_t needs at most 5 bytes, and so on. Measurements suggest
369 * that defining a separate overload for 32-bit integers is not
372 * This primitive is unsafe because it makes the size assumption and
373 * because it does not add a terminating \0.
376 inline uint32_t uint64ToBufferUnsafe(uint64_t v, char *const buffer) {
377 auto const result = digits10(v);
378 // WARNING: using size_t or pointer arithmetic for pos slows down
379 // the loop below 20x. This is because several 32-bit ops can be
380 // done in parallel, but only fewer 64-bit ones.
381 uint32_t pos = result - 1;
383 // Keep these together so a peephole optimization "sees" them and
384 // computes them in one shot.
385 auto const q = v / 10;
386 auto const r = static_cast<char>(v % 10);
387 buffer[pos--] = '0' + r;
390 // Last digit is trivial to handle
391 buffer[pos] = static_cast<char>(v) + '0';
396 * A single char gets appended.
399 void toAppend(char value, Tgt * result) {
404 constexpr typename std::enable_if<
405 std::is_same<T, char>::value,
407 estimateSpaceNeeded(T) {
412 constexpr size_t estimateSpaceNeeded(const char (&)[N]) {
417 * Everything implicitly convertible to const char* gets appended.
419 template <class Tgt, class Src>
420 typename std::enable_if<
421 std::is_convertible<Src, const char*>::value
422 && IsSomeString<Tgt>::value>::type
423 toAppend(Src value, Tgt * result) {
424 // Treat null pointers like an empty string, as in:
425 // operator<<(std::ostream&, const char*).
426 const char* c = value;
428 result->append(value);
433 typename std::enable_if<std::is_convertible<Src, const char*>::value, size_t>::
435 estimateSpaceNeeded(Src value) {
436 const char *c = value;
438 return folly::StringPiece(value).size();
444 typename std::enable_if<IsSomeString<Src>::value, size_t>::type
445 estimateSpaceNeeded(Src const& value) {
450 typename std::enable_if<
451 std::is_convertible<Src, folly::StringPiece>::value &&
452 !IsSomeString<Src>::value &&
453 !std::is_convertible<Src, const char*>::value,
455 estimateSpaceNeeded(Src value) {
456 return folly::StringPiece(value).size();
460 inline size_t estimateSpaceNeeded(std::nullptr_t /* value */) {
465 typename std::enable_if<
466 std::is_pointer<Src>::value &&
467 IsSomeString<std::remove_pointer<Src>>::value,
469 estimateSpaceNeeded(Src value) {
470 return value->size();
474 * Strings get appended, too.
476 template <class Tgt, class Src>
477 typename std::enable_if<
478 IsSomeString<Src>::value && IsSomeString<Tgt>::value>::type
479 toAppend(const Src& value, Tgt * result) {
480 result->append(value);
484 * and StringPiece objects too
487 typename std::enable_if<
488 IsSomeString<Tgt>::value>::type
489 toAppend(StringPiece value, Tgt * result) {
490 result->append(value.data(), value.size());
494 * There's no implicit conversion from fbstring to other string types,
495 * so make a specialization.
498 typename std::enable_if<
499 IsSomeString<Tgt>::value>::type
500 toAppend(const fbstring& value, Tgt * result) {
501 result->append(value.data(), value.size());
504 #if FOLLY_HAVE_INT128_T
506 * Special handling for 128 bit integers.
511 toAppend(__int128 value, Tgt * result) {
512 typedef unsigned __int128 Usrc;
513 char buffer[detail::digitsEnough<unsigned __int128>() + 1];
517 p = detail::unsafeTelescope128(buffer, sizeof(buffer), -Usrc(value));
520 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
523 result->append(buffer + p, buffer + sizeof(buffer));
528 toAppend(unsigned __int128 value, Tgt * result) {
529 char buffer[detail::digitsEnough<unsigned __int128>()];
532 p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
534 result->append(buffer + p, buffer + sizeof(buffer));
538 constexpr typename std::enable_if<
539 std::is_same<T, __int128>::value,
541 estimateSpaceNeeded(T) {
542 return detail::digitsEnough<__int128>();
546 constexpr typename std::enable_if<
547 std::is_same<T, unsigned __int128>::value,
549 estimateSpaceNeeded(T) {
550 return detail::digitsEnough<unsigned __int128>();
556 * int32_t and int64_t to string (by appending) go through here. The
557 * result is APPENDED to a preexisting string passed as the second
558 * parameter. This should be efficient with fbstring because fbstring
559 * incurs no dynamic allocation below 23 bytes and no number has more
560 * than 22 bytes in its textual representation (20 for digits, one for
561 * sign, one for the terminating 0).
563 template <class Tgt, class Src>
564 typename std::enable_if<
565 std::is_integral<Src>::value && std::is_signed<Src>::value &&
566 IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
567 toAppend(Src value, Tgt * result) {
570 result->push_back('-');
573 uint64ToBufferUnsafe(~static_cast<uint64_t>(value) + 1, buffer));
575 result->append(buffer, uint64ToBufferUnsafe(uint64_t(value), buffer));
580 typename std::enable_if<
581 std::is_integral<Src>::value && std::is_signed<Src>::value
582 && sizeof(Src) >= 4 && sizeof(Src) < 16,
584 estimateSpaceNeeded(Src value) {
586 // When "value" is the smallest negative, negating it would evoke
587 // undefined behavior, so, instead of writing "-value" below, we write
588 // "~static_cast<uint64_t>(value) + 1"
589 return 1 + digits10(~static_cast<uint64_t>(value) + 1);
592 return digits10(static_cast<uint64_t>(value));
596 * As above, but for uint32_t and uint64_t.
598 template <class Tgt, class Src>
599 typename std::enable_if<
600 std::is_integral<Src>::value && !std::is_signed<Src>::value
601 && IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
602 toAppend(Src value, Tgt * result) {
604 result->append(buffer, uint64ToBufferUnsafe(value, buffer));
608 typename std::enable_if<
609 std::is_integral<Src>::value && !std::is_signed<Src>::value
610 && sizeof(Src) >= 4 && sizeof(Src) < 16,
612 estimateSpaceNeeded(Src value) {
613 return digits10(value);
617 * All small signed and unsigned integers to string go through 32-bit
618 * types int32_t and uint32_t, respectively.
620 template <class Tgt, class Src>
621 typename std::enable_if<
622 std::is_integral<Src>::value
623 && IsSomeString<Tgt>::value && sizeof(Src) < 4>::type
624 toAppend(Src value, Tgt * result) {
626 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
628 toAppend<Tgt>(static_cast<Intermediate>(value), result);
632 typename std::enable_if<
633 std::is_integral<Src>::value
635 && !std::is_same<Src, char>::value,
637 estimateSpaceNeeded(Src value) {
639 std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
641 return estimateSpaceNeeded(static_cast<Intermediate>(value));
645 * Enumerated values get appended as integers.
647 template <class Tgt, class Src>
648 typename std::enable_if<
649 std::is_enum<Src>::value && IsSomeString<Tgt>::value>::type
650 toAppend(Src value, Tgt * result) {
652 static_cast<typename std::underlying_type<Src>::type>(value), result);
656 typename std::enable_if<
657 std::is_enum<Src>::value, size_t>::type
658 estimateSpaceNeeded(Src value) {
659 return estimateSpaceNeeded(
660 static_cast<typename std::underlying_type<Src>::type>(value));
663 /*******************************************************************************
664 * Conversions from floating-point types to string types.
665 ******************************************************************************/
668 constexpr int kConvMaxDecimalInShortestLow = -6;
669 constexpr int kConvMaxDecimalInShortestHigh = 21;
670 } // namespace detail
672 /** Wrapper around DoubleToStringConverter **/
673 template <class Tgt, class Src>
674 typename std::enable_if<
675 std::is_floating_point<Src>::value
676 && IsSomeString<Tgt>::value>::type
680 double_conversion::DoubleToStringConverter::DtoaMode mode,
681 unsigned int numDigits) {
682 using namespace double_conversion;
683 DoubleToStringConverter
684 conv(DoubleToStringConverter::NO_FLAGS,
685 "Infinity", "NaN", 'E',
686 detail::kConvMaxDecimalInShortestLow,
687 detail::kConvMaxDecimalInShortestHigh,
688 6, // max leading padding zeros
689 1); // max trailing padding zeros
691 StringBuilder builder(buffer, sizeof(buffer));
693 case DoubleToStringConverter::SHORTEST:
694 conv.ToShortest(value, &builder);
696 case DoubleToStringConverter::FIXED:
697 conv.ToFixed(value, int(numDigits), &builder);
700 CHECK(mode == DoubleToStringConverter::PRECISION);
701 conv.ToPrecision(value, int(numDigits), &builder);
704 const size_t length = size_t(builder.position());
706 result->append(buffer, length);
710 * As above, but for floating point
712 template <class Tgt, class Src>
713 typename std::enable_if<
714 std::is_floating_point<Src>::value
715 && IsSomeString<Tgt>::value>::type
716 toAppend(Src value, Tgt * result) {
718 value, result, double_conversion::DoubleToStringConverter::SHORTEST, 0);
722 * Upper bound of the length of the output from
723 * DoubleToStringConverter::ToShortest(double, StringBuilder*),
724 * as used in toAppend(double, string*).
727 typename std::enable_if<
728 std::is_floating_point<Src>::value, size_t>::type
729 estimateSpaceNeeded(Src value) {
730 // kBase10MaximalLength is 17. We add 1 for decimal point,
731 // e.g. 10.0/9 is 17 digits and 18 characters, including the decimal point.
732 constexpr int kMaxMantissaSpace =
733 double_conversion::DoubleToStringConverter::kBase10MaximalLength + 1;
734 // strlen("E-") + digits10(numeric_limits<double>::max_exponent10)
735 constexpr int kMaxExponentSpace = 2 + 3;
736 static const int kMaxPositiveSpace = std::max({
737 // E.g. 1.1111111111111111E-100.
738 kMaxMantissaSpace + kMaxExponentSpace,
739 // E.g. 0.000001.1111111111111111, if kConvMaxDecimalInShortestLow is -6.
740 kMaxMantissaSpace - detail::kConvMaxDecimalInShortestLow,
741 // If kConvMaxDecimalInShortestHigh is 21, then 1e21 is the smallest
742 // number > 1 which ToShortest outputs in exponential notation,
743 // so 21 is the longest non-exponential number > 1.
744 detail::kConvMaxDecimalInShortestHigh
748 (value < 0 ? 1 : 0)); // +1 for minus sign, if negative
752 * This can be specialized, together with adding specialization
753 * for estimateSpaceNeed for your type, so that we allocate
754 * as much as you need instead of the default
757 struct HasLengthEstimator : std::false_type {};
760 constexpr typename std::enable_if<
761 !std::is_fundamental<Src>::value
762 #if FOLLY_HAVE_INT128_T
763 // On OSX 10.10, is_fundamental<__int128> is false :-O
764 && !std::is_same<__int128, Src>::value
765 && !std::is_same<unsigned __int128, Src>::value
767 && !IsSomeString<Src>::value
768 && !std::is_convertible<Src, const char*>::value
769 && !std::is_convertible<Src, StringPiece>::value
770 && !std::is_enum<Src>::value
771 && !HasLengthEstimator<Src>::value,
773 estimateSpaceNeeded(const Src&) {
774 return sizeof(Src) + 1; // dumbest best effort ever?
780 typename std::enable_if<IsSomeString<Tgt>::value, size_t>::type
781 estimateSpaceToReserve(size_t sofar, Tgt*) {
785 template <class T, class... Ts>
786 size_t estimateSpaceToReserve(size_t sofar, const T& v, const Ts&... vs) {
787 return estimateSpaceToReserve(sofar + estimateSpaceNeeded(v), vs...);
790 template <class... Ts>
791 void reserveInTarget(const Ts&...vs) {
792 getLastElement(vs...)->reserve(estimateSpaceToReserve(0, vs...));
795 template <class Delimiter, class... Ts>
796 void reserveInTargetDelim(const Delimiter& d, const Ts&...vs) {
797 static_assert(sizeof...(vs) >= 2, "Needs at least 2 args");
798 size_t fordelim = (sizeof...(vs) - 2) *
799 estimateSpaceToReserve(0, d, static_cast<std::string*>(nullptr));
800 getLastElement(vs...)->reserve(estimateSpaceToReserve(fordelim, vs...));
804 * Variadic base case: append one element
806 template <class T, class Tgt>
807 typename std::enable_if<
808 IsSomeString<typename std::remove_pointer<Tgt>::type>
810 toAppendStrImpl(const T& v, Tgt result) {
814 template <class T, class... Ts>
815 typename std::enable_if<
816 sizeof...(Ts) >= 2 &&
817 IsSomeString<typename std::remove_pointer<
818 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
819 toAppendStrImpl(const T& v, const Ts&... vs) {
820 toAppend(v, getLastElement(vs...));
821 toAppendStrImpl(vs...);
824 template <class Delimiter, class T, class Tgt>
825 typename std::enable_if<
826 IsSomeString<typename std::remove_pointer<Tgt>::type>::value>::type
827 toAppendDelimStrImpl(const Delimiter& /* delim */, const T& v, Tgt result) {
831 template <class Delimiter, class T, class... Ts>
832 typename std::enable_if<
833 sizeof...(Ts) >= 2 &&
834 IsSomeString<typename std::remove_pointer<
835 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
836 toAppendDelimStrImpl(const Delimiter& delim, const T& v, const Ts&... vs) {
837 // we are really careful here, calling toAppend with just one element does
838 // not try to estimate space needed (as we already did that). If we call
839 // toAppend(v, delim, ....) we would do unnecesary size calculation
840 toAppend(v, detail::getLastElement(vs...));
841 toAppend(delim, detail::getLastElement(vs...));
842 toAppendDelimStrImpl(delim, vs...);
844 } // namespace detail
847 * Variadic conversion to string. Appends each element in turn.
848 * If we have two or more things to append, we it will not reserve
849 * the space for them and will depend on strings exponential growth.
850 * If you just append once consider using toAppendFit which reserves
851 * the space needed (but does not have exponential as a result).
853 * Custom implementations of toAppend() can be provided in the same namespace as
854 * the type to customize printing. estimateSpaceNeed() may also be provided to
855 * avoid reallocations in toAppendFit():
857 * namespace other_namespace {
859 * template <class String>
860 * void toAppend(const OtherType&, String* out);
863 * size_t estimateSpaceNeeded(const OtherType&);
867 template <class... Ts>
868 typename std::enable_if<
869 sizeof...(Ts) >= 3 &&
870 IsSomeString<typename std::remove_pointer<
871 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
872 toAppend(const Ts&... vs) {
873 ::folly::detail::toAppendStrImpl(vs...);
877 // Special case pid_t on MSVC, because it's a void* rather than an
878 // integral type. We can't do a global special case because this is already
879 // dangerous enough (as most pointers will implicitly convert to a void*)
880 // just doing it for MSVC.
882 void toAppend(const pid_t a, Tgt* res) {
883 toAppend(uint64_t(a), res);
888 * Special version of the call that preallocates exaclty as much memory
889 * as need for arguments to be stored in target. This means we are
890 * not doing exponential growth when we append. If you are using it
891 * in a loop you are aiming at your foot with a big perf-destroying
893 * On the other hand if you are appending to a string once, this
894 * will probably save a few calls to malloc.
896 template <class... Ts>
897 typename std::enable_if<IsSomeString<typename std::remove_pointer<
898 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
899 toAppendFit(const Ts&... vs) {
900 ::folly::detail::reserveInTarget(vs...);
905 void toAppendFit(const Ts&) {}
908 * Variadic base case: do nothing.
911 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppend(
912 Tgt* /* result */) {}
915 * Variadic base case: do nothing.
917 template <class Delimiter, class Tgt>
918 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
919 const Delimiter& /* delim */, Tgt* /* result */) {}
922 * 1 element: same as toAppend.
924 template <class Delimiter, class T, class Tgt>
925 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
926 const Delimiter& /* delim */, const T& v, Tgt* tgt) {
931 * Append to string with a delimiter in between elements. Check out
932 * comments for toAppend for details about memory allocation.
934 template <class Delimiter, class... Ts>
935 typename std::enable_if<
936 sizeof...(Ts) >= 3 &&
937 IsSomeString<typename std::remove_pointer<
938 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
939 toAppendDelim(const Delimiter& delim, const Ts&... vs) {
940 detail::toAppendDelimStrImpl(delim, vs...);
944 * Detail in comment for toAppendFit
946 template <class Delimiter, class... Ts>
947 typename std::enable_if<IsSomeString<typename std::remove_pointer<
948 typename detail::LastElement<const Ts&...>::type>::type>::value>::type
949 toAppendDelimFit(const Delimiter& delim, const Ts&... vs) {
950 detail::reserveInTargetDelim(delim, vs...);
951 toAppendDelim(delim, vs...);
954 template <class De, class Ts>
955 void toAppendDelimFit(const De&, const Ts&) {}
958 * to<SomeString>(v1, v2, ...) uses toAppend() (see below) as back-end
961 template <class Tgt, class... Ts>
962 typename std::enable_if<
963 IsSomeString<Tgt>::value &&
964 (sizeof...(Ts) != 1 ||
965 !std::is_same<Tgt, typename detail::LastElement<const Ts&...>::type>::
968 to(const Ts&... vs) {
970 toAppendFit(vs..., &result);
975 * Special version of to<SomeString> for floating point. When calling
976 * folly::to<SomeString>(double), generic implementation above will
977 * firstly reserve 24 (or 25 when negative value) bytes. This will
978 * introduce a malloc call for most mainstream string implementations.
980 * But for most cases, a floating point doesn't need 24 (or 25) bytes to
981 * be converted as a string.
983 * This special version will not do string reserve.
985 template <class Tgt, class Src>
986 typename std::enable_if<
987 IsSomeString<Tgt>::value && std::is_floating_point<Src>::value,
991 toAppend(value, &result);
996 * toDelim<SomeString>(SomeString str) returns itself.
998 template <class Tgt, class Delim, class Src>
999 typename std::enable_if<
1000 IsSomeString<Tgt>::value &&
1001 std::is_same<Tgt, typename std::decay<Src>::type>::value,
1003 toDelim(const Delim& /* delim */, Src&& value) {
1004 return std::forward<Src>(value);
1008 * toDelim<SomeString>(delim, v1, v2, ...) uses toAppendDelim() as
1009 * back-end for all types.
1011 template <class Tgt, class Delim, class... Ts>
1012 typename std::enable_if<
1013 IsSomeString<Tgt>::value &&
1014 (sizeof...(Ts) != 1 ||
1015 !std::is_same<Tgt, typename detail::LastElement<const Ts&...>::type>::
1018 toDelim(const Delim& delim, const Ts&... vs) {
1020 toAppendDelimFit(delim, vs..., &result);
1024 /*******************************************************************************
1025 * Conversions from string types to integral types.
1026 ******************************************************************************/
1030 Expected<bool, ConversionCode> str_to_bool(StringPiece* src) noexcept;
1032 template <typename T>
1033 Expected<T, ConversionCode> str_to_floating(StringPiece* src) noexcept;
1035 extern template Expected<float, ConversionCode> str_to_floating<float>(
1036 StringPiece* src) noexcept;
1037 extern template Expected<double, ConversionCode> str_to_floating<double>(
1038 StringPiece* src) noexcept;
1040 template <class Tgt>
1041 Expected<Tgt, ConversionCode> digits_to(const char* b, const char* e) noexcept;
1043 extern template Expected<char, ConversionCode> digits_to<char>(
1045 const char*) noexcept;
1046 extern template Expected<signed char, ConversionCode> digits_to<signed char>(
1048 const char*) noexcept;
1049 extern template Expected<unsigned char, ConversionCode>
1050 digits_to<unsigned char>(const char*, const char*) noexcept;
1052 extern template Expected<short, ConversionCode> digits_to<short>(
1054 const char*) noexcept;
1055 extern template Expected<unsigned short, ConversionCode>
1056 digits_to<unsigned short>(const char*, const char*) noexcept;
1058 extern template Expected<int, ConversionCode> digits_to<int>(
1060 const char*) noexcept;
1061 extern template Expected<unsigned int, ConversionCode> digits_to<unsigned int>(
1063 const char*) noexcept;
1065 extern template Expected<long, ConversionCode> digits_to<long>(
1067 const char*) noexcept;
1068 extern template Expected<unsigned long, ConversionCode>
1069 digits_to<unsigned long>(const char*, const char*) noexcept;
1071 extern template Expected<long long, ConversionCode> digits_to<long long>(
1073 const char*) noexcept;
1074 extern template Expected<unsigned long long, ConversionCode>
1075 digits_to<unsigned long long>(const char*, const char*) noexcept;
1077 #if FOLLY_HAVE_INT128_T
1078 extern template Expected<__int128, ConversionCode> digits_to<__int128>(
1080 const char*) noexcept;
1081 extern template Expected<unsigned __int128, ConversionCode>
1082 digits_to<unsigned __int128>(const char*, const char*) noexcept;
1086 Expected<T, ConversionCode> str_to_integral(StringPiece* src) noexcept;
1088 extern template Expected<char, ConversionCode> str_to_integral<char>(
1089 StringPiece* src) noexcept;
1090 extern template Expected<signed char, ConversionCode>
1091 str_to_integral<signed char>(StringPiece* src) noexcept;
1092 extern template Expected<unsigned char, ConversionCode>
1093 str_to_integral<unsigned char>(StringPiece* src) noexcept;
1095 extern template Expected<short, ConversionCode> str_to_integral<short>(
1096 StringPiece* src) noexcept;
1097 extern template Expected<unsigned short, ConversionCode>
1098 str_to_integral<unsigned short>(StringPiece* src) noexcept;
1100 extern template Expected<int, ConversionCode> str_to_integral<int>(
1101 StringPiece* src) noexcept;
1102 extern template Expected<unsigned int, ConversionCode>
1103 str_to_integral<unsigned int>(StringPiece* src) noexcept;
1105 extern template Expected<long, ConversionCode> str_to_integral<long>(
1106 StringPiece* src) noexcept;
1107 extern template Expected<unsigned long, ConversionCode>
1108 str_to_integral<unsigned long>(StringPiece* src) noexcept;
1110 extern template Expected<long long, ConversionCode> str_to_integral<long long>(
1111 StringPiece* src) noexcept;
1112 extern template Expected<unsigned long long, ConversionCode>
1113 str_to_integral<unsigned long long>(StringPiece* src) noexcept;
1115 #if FOLLY_HAVE_INT128_T
1116 extern template Expected<__int128, ConversionCode> str_to_integral<__int128>(
1117 StringPiece* src) noexcept;
1118 extern template Expected<unsigned __int128, ConversionCode>
1119 str_to_integral<unsigned __int128>(StringPiece* src) noexcept;
1122 template <typename T>
1124 enable_if<std::is_same<T, bool>::value, Expected<T, ConversionCode>>::type
1125 convertTo(StringPiece* src) noexcept {
1126 return str_to_bool(src);
1129 template <typename T>
1130 typename std::enable_if<
1131 std::is_floating_point<T>::value,
1132 Expected<T, ConversionCode>>::type
1133 convertTo(StringPiece* src) noexcept {
1134 return str_to_floating<T>(src);
1137 template <typename T>
1138 typename std::enable_if<
1139 std::is_integral<T>::value && !std::is_same<T, bool>::value,
1140 Expected<T, ConversionCode>>::type
1141 convertTo(StringPiece* src) noexcept {
1142 return str_to_integral<T>(src);
1145 } // namespace detail
1148 * String represented as a pair of pointers to char to unsigned
1149 * integrals. Assumes NO whitespace before or after.
1151 template <typename Tgt>
1152 typename std::enable_if<
1153 std::is_integral<Tgt>::value && !std::is_same<Tgt, bool>::value,
1154 Expected<Tgt, ConversionCode>>::type
1155 tryTo(const char* b, const char* e) {
1156 return detail::digits_to<Tgt>(b, e);
1159 template <typename Tgt>
1160 typename std::enable_if<
1161 std::is_integral<Tgt>::value && !std::is_same<Tgt, bool>::value,
1163 to(const char* b, const char* e) {
1164 return tryTo<Tgt>(b, e).thenOrThrow(
1165 [](Tgt res) { return res; },
1166 [=](ConversionCode code) {
1167 return makeConversionError(code, StringPiece(b, e));
1171 /*******************************************************************************
1172 * Conversions from string types to arithmetic types.
1173 ******************************************************************************/
1176 * Parsing strings to numeric types.
1178 template <typename Tgt>
1179 FOLLY_NODISCARD inline typename std::enable_if<
1180 std::is_arithmetic<Tgt>::value,
1181 Expected<StringPiece, ConversionCode>>::type
1182 parseTo(StringPiece src, Tgt& out) {
1183 return detail::convertTo<Tgt>(&src).then(
1184 [&](Tgt res) { return void(out = res), src; });
1187 /*******************************************************************************
1188 * Integral / Floating Point to integral / Floating Point
1189 ******************************************************************************/
1194 * Bool to integral/float doesn't need any special checks, and this
1195 * overload means we aren't trying to see if a bool is less than
1198 template <class Tgt>
1199 typename std::enable_if<
1200 !std::is_same<Tgt, bool>::value &&
1201 (std::is_integral<Tgt>::value || std::is_floating_point<Tgt>::value),
1202 Expected<Tgt, ConversionCode>>::type
1203 convertTo(const bool& value) noexcept {
1204 return static_cast<Tgt>(value ? 1 : 0);
1208 * Checked conversion from integral to integral. The checks are only
1209 * performed when meaningful, e.g. conversion from int to long goes
1212 template <class Tgt, class Src>
1213 typename std::enable_if<
1214 std::is_integral<Src>::value && !std::is_same<Tgt, Src>::value &&
1215 !std::is_same<Tgt, bool>::value &&
1216 std::is_integral<Tgt>::value,
1217 Expected<Tgt, ConversionCode>>::type
1218 convertTo(const Src& value) noexcept {
1220 folly::_t<std::make_unsigned<Tgt>>(std::numeric_limits<Tgt>::max()) <
1221 folly::_t<std::make_unsigned<Src>>(std::numeric_limits<Src>::max())) {
1222 if (greater_than<Tgt, std::numeric_limits<Tgt>::max()>(value)) {
1223 return makeUnexpected(ConversionCode::ARITH_POSITIVE_OVERFLOW);
1227 std::is_signed<Src>::value &&
1228 (!std::is_signed<Tgt>::value || sizeof(Src) > sizeof(Tgt))) {
1229 if (less_than<Tgt, std::numeric_limits<Tgt>::min()>(value)) {
1230 return makeUnexpected(ConversionCode::ARITH_NEGATIVE_OVERFLOW);
1233 return static_cast<Tgt>(value);
1237 * Checked conversion from floating to floating. The checks are only
1238 * performed when meaningful, e.g. conversion from float to double goes
1241 template <class Tgt, class Src>
1242 typename std::enable_if<
1243 std::is_floating_point<Tgt>::value && std::is_floating_point<Src>::value &&
1244 !std::is_same<Tgt, Src>::value,
1245 Expected<Tgt, ConversionCode>>::type
1246 convertTo(const Src& value) noexcept {
1248 std::numeric_limits<Tgt>::max() < std::numeric_limits<Src>::max()) {
1249 if (value > std::numeric_limits<Tgt>::max()) {
1250 return makeUnexpected(ConversionCode::ARITH_POSITIVE_OVERFLOW);
1252 if (value < std::numeric_limits<Tgt>::lowest()) {
1253 return makeUnexpected(ConversionCode::ARITH_NEGATIVE_OVERFLOW);
1256 return static_cast<Tgt>(value);
1260 * Check if a floating point value can safely be converted to an
1261 * integer value without triggering undefined behaviour.
1263 template <typename Tgt, typename Src>
1264 inline typename std::enable_if<
1265 std::is_floating_point<Src>::value && std::is_integral<Tgt>::value &&
1266 !std::is_same<Tgt, bool>::value,
1268 checkConversion(const Src& value) {
1269 constexpr Src tgtMaxAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::max());
1270 constexpr Src tgtMinAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::min());
1271 if (value >= tgtMaxAsSrc) {
1272 if (value > tgtMaxAsSrc) {
1275 const Src mmax = folly::nextafter(tgtMaxAsSrc, Src());
1276 if (static_cast<Tgt>(value - mmax) >
1277 std::numeric_limits<Tgt>::max() - static_cast<Tgt>(mmax)) {
1280 } else if (std::is_signed<Tgt>::value && value <= tgtMinAsSrc) {
1281 if (value < tgtMinAsSrc) {
1284 const Src mmin = folly::nextafter(tgtMinAsSrc, Src());
1285 if (static_cast<Tgt>(value - mmin) <
1286 std::numeric_limits<Tgt>::min() - static_cast<Tgt>(mmin)) {
1293 // Integers can always safely be converted to floating point values
1294 template <typename Tgt, typename Src>
1295 constexpr typename std::enable_if<
1296 std::is_integral<Src>::value && std::is_floating_point<Tgt>::value,
1298 checkConversion(const Src&) {
1302 // Also, floating point values can always be safely converted to bool
1303 // Per the standard, any floating point value that is not zero will yield true
1304 template <typename Tgt, typename Src>
1305 constexpr typename std::enable_if<
1306 std::is_floating_point<Src>::value && std::is_same<Tgt, bool>::value,
1308 checkConversion(const Src&) {
1313 * Checked conversion from integral to floating point and back. The
1314 * result must be convertible back to the source type without loss of
1315 * precision. This seems Draconian but sometimes is what's needed, and
1316 * complements existing routines nicely. For various rounding
1317 * routines, see <math>.
1319 template <typename Tgt, typename Src>
1320 typename std::enable_if<
1321 (std::is_integral<Src>::value && std::is_floating_point<Tgt>::value) ||
1322 (std::is_floating_point<Src>::value && std::is_integral<Tgt>::value),
1323 Expected<Tgt, ConversionCode>>::type
1324 convertTo(const Src& value) noexcept {
1325 if (LIKELY(checkConversion<Tgt>(value))) {
1326 Tgt result = static_cast<Tgt>(value);
1327 if (LIKELY(checkConversion<Src>(result))) {
1328 Src witness = static_cast<Src>(result);
1329 if (LIKELY(value == witness)) {
1334 return makeUnexpected(ConversionCode::ARITH_LOSS_OF_PRECISION);
1337 template <typename Tgt, typename Src>
1338 inline std::string errorValue(const Src& value) {
1339 #ifdef FOLLY_HAS_RTTI
1340 return to<std::string>("(", demangle(typeid(Tgt)), ") ", value);
1342 return to<std::string>(value);
1346 template <typename Tgt, typename Src>
1347 using IsArithToArith = std::integral_constant<
1349 !std::is_same<Tgt, Src>::value && !std::is_same<Tgt, bool>::value &&
1350 std::is_arithmetic<Src>::value &&
1351 std::is_arithmetic<Tgt>::value>;
1353 } // namespace detail
1355 template <typename Tgt, typename Src>
1356 typename std::enable_if<
1357 detail::IsArithToArith<Tgt, Src>::value,
1358 Expected<Tgt, ConversionCode>>::type
1359 tryTo(const Src& value) noexcept {
1360 return detail::convertTo<Tgt>(value);
1363 template <typename Tgt, typename Src>
1364 typename std::enable_if<detail::IsArithToArith<Tgt, Src>::value, Tgt>::type to(
1366 return tryTo<Tgt>(value).thenOrThrow(
1367 [](Tgt res) { return res; },
1368 [&](ConversionCode e) {
1369 return makeConversionError(e, detail::errorValue<Tgt>(value));
1373 /*******************************************************************************
1374 * Custom Conversions
1376 * Any type can be used with folly::to by implementing parseTo. The
1377 * implementation should be provided in the namespace of the type to facilitate
1378 * argument-dependent lookup:
1380 * namespace other_namespace {
1381 * ::folly::Expected<::folly::StringPiece, SomeErrorCode>
1382 * parseTo(::folly::StringPiece, OtherType&) noexcept;
1384 ******************************************************************************/
1386 FOLLY_NODISCARD typename std::enable_if<
1387 std::is_enum<T>::value,
1388 Expected<StringPiece, ConversionCode>>::type
1389 parseTo(StringPiece in, T& out) noexcept {
1390 typename std::underlying_type<T>::type tmp{};
1391 auto restOrError = parseTo(in, tmp);
1392 out = static_cast<T>(tmp); // Harmless if parseTo fails
1397 inline Expected<StringPiece, ConversionCode> parseTo(
1399 StringPiece& out) noexcept {
1401 return StringPiece{in.end(), in.end()};
1405 inline Expected<StringPiece, ConversionCode> parseTo(
1409 out.append(in.data(), in.size()); // TODO try/catch?
1410 return StringPiece{in.end(), in.end()};
1414 inline Expected<StringPiece, ConversionCode> parseTo(
1418 out.append(in.data(), in.size()); // TODO try/catch?
1419 return StringPiece{in.end(), in.end()};
1423 template <typename Tgt>
1424 using ParseToResult = decltype(parseTo(StringPiece{}, std::declval<Tgt&>()));
1426 struct CheckTrailingSpace {
1427 Expected<Unit, ConversionCode> operator()(StringPiece sp) const {
1428 auto e = enforceWhitespaceErr(sp);
1429 if (UNLIKELY(e != ConversionCode::SUCCESS)) {
1430 return makeUnexpected(e);
1436 template <class Error>
1439 constexpr Expected<Unit, Error> operator()(T&&) const {
1444 // Older versions of the parseTo customization point threw on error and
1445 // returned void. Handle that.
1446 template <class Tgt>
1447 inline typename std::enable_if<
1448 std::is_void<ParseToResult<Tgt>>::value,
1449 Expected<StringPiece, ConversionCode>>::type
1450 parseToWrap(StringPiece sp, Tgt& out) {
1452 return StringPiece(sp.end(), sp.end());
1455 template <class Tgt>
1456 inline typename std::enable_if<
1457 !std::is_void<ParseToResult<Tgt>>::value,
1458 ParseToResult<Tgt>>::type
1459 parseToWrap(StringPiece sp, Tgt& out) {
1460 return parseTo(sp, out);
1463 template <typename Tgt>
1464 using ParseToError = ExpectedErrorType<decltype(
1465 detail::parseToWrap(StringPiece{}, std::declval<Tgt&>()))>;
1467 } // namespace detail
1470 * String or StringPiece to target conversion. Accepts leading and trailing
1471 * whitespace, but no non-space trailing characters.
1474 template <class Tgt>
1475 inline typename std::enable_if<
1476 !std::is_same<StringPiece, Tgt>::value,
1477 Expected<Tgt, detail::ParseToError<Tgt>>>::type
1478 tryTo(StringPiece src) {
1480 using Error = detail::ParseToError<Tgt>;
1481 using Check = typename std::conditional<
1482 std::is_arithmetic<Tgt>::value,
1483 detail::CheckTrailingSpace,
1484 detail::ReturnUnit<Error>>::type;
1485 return parseTo(src, result).then(Check(), [&](Unit) {
1486 return std::move(result);
1490 template <class Tgt, class Src>
1491 inline typename std::enable_if<
1492 IsSomeString<Src>::value && !std::is_same<StringPiece, Tgt>::value,
1494 to(Src const& src) {
1495 return to<Tgt>(StringPiece(src.data(), src.size()));
1498 template <class Tgt>
1500 typename std::enable_if<!std::is_same<StringPiece, Tgt>::value, Tgt>::type
1501 to(StringPiece src) {
1503 using Error = detail::ParseToError<Tgt>;
1504 using Check = typename std::conditional<
1505 std::is_arithmetic<Tgt>::value,
1506 detail::CheckTrailingSpace,
1507 detail::ReturnUnit<Error>>::type;
1508 auto tmp = detail::parseToWrap(src, result);
1510 .thenOrThrow(Check(), [&](Error e) { throw makeConversionError(e, src); })
1512 [&](Unit) { return std::move(result); },
1513 [&](Error e) { throw makeConversionError(e, tmp.value()); });
1517 * tryTo/to that take the strings by pointer so the caller gets information
1518 * about how much of the string was consumed by the conversion. These do not
1519 * check for trailing whitepsace.
1521 template <class Tgt>
1522 Expected<Tgt, detail::ParseToError<Tgt>> tryTo(StringPiece* src) {
1524 return parseTo(*src, result).then([&, src](StringPiece sp) -> Tgt {
1526 return std::move(result);
1530 template <class Tgt>
1531 Tgt to(StringPiece* src) {
1533 using Error = detail::ParseToError<Tgt>;
1534 return parseTo(*src, result)
1536 [&, src](StringPiece sp) -> Tgt {
1538 return std::move(result);
1540 [=](Error e) { return makeConversionError(e, *src); });
1543 /*******************************************************************************
1544 * Enum to anything and back
1545 ******************************************************************************/
1547 template <class Tgt, class Src>
1548 typename std::enable_if<
1549 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value,
1550 Expected<Tgt, ConversionCode>>::type
1551 tryTo(const Src& value) {
1552 using I = typename std::underlying_type<Src>::type;
1553 return tryTo<Tgt>(static_cast<I>(value));
1556 template <class Tgt, class Src>
1557 typename std::enable_if<
1558 std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value,
1559 Expected<Tgt, ConversionCode>>::type
1560 tryTo(const Src& value) {
1561 using I = typename std::underlying_type<Tgt>::type;
1562 return tryTo<I>(value).then([](I i) { return static_cast<Tgt>(i); });
1565 template <class Tgt, class Src>
1566 typename std::enable_if<
1567 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value,
1569 to(const Src& value) {
1570 return to<Tgt>(static_cast<typename std::underlying_type<Src>::type>(value));
1573 template <class Tgt, class Src>
1574 typename std::enable_if<
1575 !IsSomeString<Src>::value && std::is_enum<Tgt>::value &&
1576 !std::is_same<Src, Tgt>::value,
1578 to(const Src& value) {
1579 return static_cast<Tgt>(to<typename std::underlying_type<Tgt>::type>(value));
1582 } // namespace folly