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)
26 #include <folly/FBString.h>
27 #include <folly/Likely.h>
28 #include <folly/Preprocessor.h>
29 #include <folly/Range.h>
31 #include <boost/implicit_cast.hpp>
33 #include <type_traits>
42 // V8 JavaScript implementation
43 #include <double-conversion/double-conversion.h>
45 #define FOLLY_RANGE_CHECK_STRINGIZE(x) #x
46 #define FOLLY_RANGE_CHECK_STRINGIZE2(x) FOLLY_RANGE_CHECK_STRINGIZE(x)
48 // Android doesn't support std::to_string so just use a placeholder there.
50 #define FOLLY_RANGE_CHECK_TO_STRING(x) std::string("N/A")
52 #define FOLLY_RANGE_CHECK_TO_STRING(x) std::to_string(x)
55 #define FOLLY_RANGE_CHECK(condition, message, src) \
56 ((condition) ? (void)0 : throw std::range_error( \
57 (std::string(__FILE__ "(" FOLLY_RANGE_CHECK_STRINGIZE2(__LINE__) "): ") \
58 + (message) + ": '" + (src) + "'").c_str()))
60 #define FOLLY_RANGE_CHECK_BEGIN_END(condition, message, b, e) \
61 FOLLY_RANGE_CHECK(condition, message, std::string((b), (e) - (b)))
63 #define FOLLY_RANGE_CHECK_STRINGPIECE(condition, message, sp) \
64 FOLLY_RANGE_CHECK(condition, message, std::string((sp).data(), (sp).size()))
69 * The identity conversion function.
70 * to<T>(T) returns itself for all types T.
72 template <class Tgt, class Src>
73 typename std::enable_if<std::is_same<Tgt, Src>::value, Tgt>::type
74 to(const Src & value) {
78 template <class Tgt, class Src>
79 typename std::enable_if<std::is_same<Tgt, Src>::value, Tgt>::type
81 return std::forward<Src>(value);
84 /*******************************************************************************
85 * Integral to integral
86 ******************************************************************************/
89 * Unchecked conversion from integral to boolean. This is different from the
90 * other integral conversions because we use the C convention of treating any
91 * non-zero value as true, instead of range checking.
93 template <class Tgt, class Src>
94 typename std::enable_if<
95 std::is_integral<Src>::value
96 && !std::is_same<Tgt, Src>::value
97 && std::is_same<Tgt, bool>::value,
99 to(const Src & value) {
104 * Checked conversion from integral to integral. The checks are only
105 * performed when meaningful, e.g. conversion from int to long goes
108 template <class Tgt, class Src>
109 typename std::enable_if<
110 std::is_integral<Src>::value
111 && !std::is_same<Tgt, Src>::value
112 && !std::is_same<Tgt, bool>::value
113 && std::is_integral<Tgt>::value,
115 to(const Src & value) {
116 /* static */ if (std::numeric_limits<Tgt>::max()
117 < std::numeric_limits<Src>::max()) {
119 (!greater_than<Tgt, std::numeric_limits<Tgt>::max()>(value)),
121 FOLLY_RANGE_CHECK_TO_STRING(value));
123 /* static */ if (std::is_signed<Src>::value &&
124 (!std::is_signed<Tgt>::value || sizeof(Src) > sizeof(Tgt))) {
126 (!less_than<Tgt, std::numeric_limits<Tgt>::min()>(value)),
128 FOLLY_RANGE_CHECK_TO_STRING(value));
130 return static_cast<Tgt>(value);
133 /*******************************************************************************
134 * Floating point to floating point
135 ******************************************************************************/
137 template <class Tgt, class Src>
138 typename std::enable_if<
139 std::is_floating_point<Tgt>::value
140 && std::is_floating_point<Src>::value
141 && !std::is_same<Tgt, Src>::value,
143 to(const Src & value) {
144 /* static */ if (std::numeric_limits<Tgt>::max() <
145 std::numeric_limits<Src>::max()) {
146 FOLLY_RANGE_CHECK(value <= std::numeric_limits<Tgt>::max(),
148 FOLLY_RANGE_CHECK_TO_STRING(value));
149 FOLLY_RANGE_CHECK(value >= -std::numeric_limits<Tgt>::max(),
151 FOLLY_RANGE_CHECK_TO_STRING(value));
153 return boost::implicit_cast<Tgt>(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, 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 #ifdef 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?
722 inline size_t estimateSpaceToReserve(size_t sofar) {
726 template <class T, class... Ts>
727 size_t estimateSpaceToReserve(size_t sofar, const T& v, const Ts&... vs) {
728 return estimateSpaceToReserve(sofar + estimateSpaceNeeded(v), vs...);
732 size_t estimateSpaceToReserve(size_t sofar, const T& v) {
733 return sofar + estimateSpaceNeeded(v);
737 void reserveInTarget(const Ts&...vs) {
738 getLastElement(vs...)->reserve(estimateSpaceToReserve(0, vs...));
741 template<class Delimiter, class...Ts>
742 void reserveInTargetDelim(const Delimiter& d, const Ts&...vs) {
743 static_assert(sizeof...(vs) >= 2, "Needs at least 2 args");
744 size_t fordelim = (sizeof...(vs) - 2) * estimateSpaceToReserve(0, d);
745 getLastElement(vs...)->reserve(estimateSpaceToReserve(fordelim, vs...));
749 * Variadic base case: append one element
751 template <class T, class Tgt>
752 typename std::enable_if<
753 IsSomeString<typename std::remove_pointer<Tgt>::type>
755 toAppendStrImpl(const T& v, Tgt result) {
759 template <class T, class... Ts>
760 typename std::enable_if<sizeof...(Ts) >= 2
762 typename std::remove_pointer<
763 typename detail::last_element<Ts...>::type
764 >::type>::value>::type
765 toAppendStrImpl(const T& v, const Ts&... vs) {
766 toAppend(v, getLastElement(vs...));
767 toAppendStrImpl(vs...);
770 template <class Delimiter, class T, class Tgt>
771 typename std::enable_if<
772 IsSomeString<typename std::remove_pointer<Tgt>::type>::value>::type
773 toAppendDelimStrImpl(const Delimiter& /* delim */, const T& v, Tgt result) {
777 template <class Delimiter, class T, class... Ts>
778 typename std::enable_if<sizeof...(Ts) >= 2
780 typename std::remove_pointer<
781 typename detail::last_element<Ts...>::type
782 >::type>::value>::type
783 toAppendDelimStrImpl(const Delimiter& delim, const T& v, const Ts&... vs) {
784 // we are really careful here, calling toAppend with just one element does
785 // not try to estimate space needed (as we already did that). If we call
786 // toAppend(v, delim, ....) we would do unnecesary size calculation
787 toAppend(v, detail::getLastElement(vs...));
788 toAppend(delim, detail::getLastElement(vs...));
789 toAppendDelimStrImpl(delim, vs...);
795 * Variadic conversion to string. Appends each element in turn.
796 * If we have two or more things to append, we it will not reserve
797 * the space for them and will depend on strings exponential growth.
798 * If you just append once consider using toAppendFit which reserves
799 * the space needed (but does not have exponential as a result).
801 * Custom implementations of toAppend() can be provided in the same namespace as
802 * the type to customize printing. estimateSpaceNeed() may also be provided to
803 * avoid reallocations in toAppendFit():
805 * namespace other_namespace {
807 * template <class String>
808 * void toAppend(const OtherType&, String* out);
811 * size_t estimateSpaceNeeded(const OtherType&);
815 template <class... Ts>
816 typename std::enable_if<sizeof...(Ts) >= 3
818 typename std::remove_pointer<
819 typename detail::last_element<Ts...>::type
820 >::type>::value>::type
821 toAppend(const Ts&... vs) {
822 ::folly::detail::toAppendStrImpl(vs...);
826 // Special case pid_t on MSVC, because it's a void* rather than an
827 // integral type. We can't do a global special case because this is already
828 // dangerous enough (as most pointers will implicitly convert to a void*)
829 // just doing it for MSVC.
831 void toAppend(const pid_t a, Tgt* res) {
832 toAppend(uint64_t(a), res);
837 * Special version of the call that preallocates exaclty as much memory
838 * as need for arguments to be stored in target. This means we are
839 * not doing exponential growth when we append. If you are using it
840 * in a loop you are aiming at your foot with a big perf-destroying
842 * On the other hand if you are appending to a string once, this
843 * will probably save a few calls to malloc.
845 template <class... Ts>
846 typename std::enable_if<
848 typename std::remove_pointer<
849 typename detail::last_element<Ts...>::type
850 >::type>::value>::type
851 toAppendFit(const Ts&... vs) {
852 ::folly::detail::reserveInTarget(vs...);
857 void toAppendFit(const Ts&) {}
860 * Variadic base case: do nothing.
863 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppend(
864 Tgt* /* result */) {}
867 * Variadic base case: do nothing.
869 template <class Delimiter, class Tgt>
870 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
871 const Delimiter& /* delim */, Tgt* /* result */) {}
874 * 1 element: same as toAppend.
876 template <class Delimiter, class T, class Tgt>
877 typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
878 const Delimiter& /* delim */, const T& v, Tgt* tgt) {
883 * Append to string with a delimiter in between elements. Check out
884 * comments for toAppend for details about memory allocation.
886 template <class Delimiter, class... Ts>
887 typename std::enable_if<sizeof...(Ts) >= 3
889 typename std::remove_pointer<
890 typename detail::last_element<Ts...>::type
891 >::type>::value>::type
892 toAppendDelim(const Delimiter& delim, const Ts&... vs) {
893 detail::toAppendDelimStrImpl(delim, vs...);
897 * Detail in comment for toAppendFit
899 template <class Delimiter, class... Ts>
900 typename std::enable_if<
902 typename std::remove_pointer<
903 typename detail::last_element<Ts...>::type
904 >::type>::value>::type
905 toAppendDelimFit(const Delimiter& delim, const Ts&... vs) {
906 detail::reserveInTargetDelim(delim, vs...);
907 toAppendDelim(delim, vs...);
910 template <class De, class Ts>
911 void toAppendDelimFit(const De&, const Ts&) {}
914 * to<SomeString>(v1, v2, ...) uses toAppend() (see below) as back-end
917 template <class Tgt, class... Ts>
918 typename std::enable_if<
919 IsSomeString<Tgt>::value && (
920 sizeof...(Ts) != 1 ||
921 !std::is_same<Tgt, typename detail::last_element<Ts...>::type>::value),
923 to(const Ts&... vs) {
925 toAppendFit(vs..., &result);
930 * toDelim<SomeString>(SomeString str) returns itself.
932 template <class Tgt, class Delim, class Src>
933 typename std::enable_if<IsSomeString<Tgt>::value &&
934 std::is_same<Tgt, Src>::value,
936 toDelim(const Delim& /* delim */, const Src& value) {
941 * toDelim<SomeString>(delim, v1, v2, ...) uses toAppendDelim() as
942 * back-end for all types.
944 template <class Tgt, class Delim, class... Ts>
945 typename std::enable_if<
946 IsSomeString<Tgt>::value && (
947 sizeof...(Ts) != 1 ||
948 !std::is_same<Tgt, typename detail::last_element<Ts...>::type>::value),
950 toDelim(const Delim& delim, const Ts&... vs) {
952 toAppendDelimFit(delim, vs..., &result);
956 /*******************************************************************************
957 * Conversions from string types to integral types.
958 ******************************************************************************/
963 * Finds the first non-digit in a string. The number of digits
964 * searched depends on the precision of the Tgt integral. Assumes the
965 * string starts with NO whitespace and NO sign.
967 * The semantics of the routine is:
969 * if (b >= e || !isdigit(*b)) return b;
972 * Complete unrolling marks bottom-line (i.e. entire conversion)
973 * improvements of 20%.
976 const char* findFirstNonDigit(const char* b, const char* e) {
978 auto const c = static_cast<unsigned>(*b) - '0';
984 // Maximum value of number when represented as a string
985 template <class T> struct MaxString {
986 static const char*const value;
989 bool str_to_bool(StringPiece* src);
990 float str_to_float(StringPiece* src);
991 double str_to_double(StringPiece* src);
994 Tgt digits_to(const char* b, const char* e);
996 extern template unsigned char digits_to<unsigned char>(const char* b,
998 extern template unsigned short digits_to<unsigned short>(const char* b,
1000 extern template unsigned int digits_to<unsigned int>(const char* b,
1002 extern template unsigned long digits_to<unsigned long>(const char* b,
1004 extern template unsigned long long digits_to<unsigned long long>(
1005 const char* b, const char* e);
1006 #if FOLLY_HAVE_INT128_T
1007 extern template unsigned __int128 digits_to<unsigned __int128>(const char* b,
1011 } // namespace detail
1014 * String represented as a pair of pointers to char to unsigned
1015 * integrals. Assumes NO whitespace before or after.
1017 template <class Tgt>
1018 typename std::enable_if<
1019 std::is_integral<Tgt>::value && !std::is_signed<Tgt>::value
1020 && !std::is_same<typename std::remove_cv<Tgt>::type, bool>::value,
1022 to(const char * b, const char * e) {
1023 return detail::digits_to<Tgt>(b, e);
1027 * String represented as a pair of pointers to char to signed
1028 * integrals. Assumes NO whitespace before or after. Allows an
1029 * optional leading sign.
1031 template <class Tgt>
1032 typename std::enable_if<
1033 std::is_integral<Tgt>::value && std::is_signed<Tgt>::value,
1035 to(const char * b, const char * e) {
1036 FOLLY_RANGE_CHECK(b < e, "Empty input string in conversion to integral",
1037 to<std::string>("b: ", intptr_t(b), " e: ", intptr_t(e)));
1040 Tgt result = -to<typename std::make_unsigned<Tgt>::type>(b + 1, e);
1041 FOLLY_RANGE_CHECK_BEGIN_END(result <= 0, "Negative overflow.", b, e);
1044 FOLLY_RANGE_CHECK_BEGIN_END(*b == '+', "Invalid lead character", b, e);
1047 Tgt result = to<typename std::make_unsigned<Tgt>::type>(b, e);
1048 FOLLY_RANGE_CHECK_BEGIN_END(result >= 0, "Overflow", b, e);
1054 * StringPiece to integrals, with progress information. Alters the
1055 * StringPiece parameter to munch the already-parsed characters.
1057 template <class Tgt>
1058 Tgt str_to_integral(StringPiece* src) {
1059 auto b = src->data(), past = src->data() + src->size();
1061 FOLLY_RANGE_CHECK_STRINGPIECE(b < past,
1062 "No digits found in input string", *src);
1063 if (!isspace(*b)) break;
1068 // First digit is customized because we test for sign
1069 bool negative = false;
1070 /* static */ if (std::is_signed<Tgt>::value) {
1075 FOLLY_RANGE_CHECK_STRINGPIECE(*m == '+', "Invalid leading character in "
1076 "conversion to integral", *src);
1082 FOLLY_RANGE_CHECK_STRINGPIECE(m < past, "No digits found in input string",
1084 FOLLY_RANGE_CHECK_STRINGPIECE(isdigit(*m), "Non-digit character found", *src);
1085 m = detail::findFirstNonDigit<Tgt>(m + 1, past);
1088 /* static */ if (!std::is_signed<Tgt>::value) {
1089 result = detail::digits_to<typename std::make_unsigned<Tgt>::type>(b, m);
1091 auto t = detail::digits_to<typename std::make_unsigned<Tgt>::type>(b, m);
1094 FOLLY_RANGE_CHECK_STRINGPIECE(is_non_positive(result),
1095 "Negative overflow", *src);
1098 FOLLY_RANGE_CHECK_STRINGPIECE(is_non_negative(result), "Overflow", *src);
1101 src->advance(m - src->data());
1106 * Enforce that the suffix following a number is made up only of whitespace.
1108 inline void enforceWhitespace(StringPiece sp) {
1109 for (char ch : sp) {
1110 FOLLY_RANGE_CHECK_STRINGPIECE(
1111 isspace(ch), to<std::string>("Non-whitespace: ", ch), sp);
1115 /*******************************************************************************
1116 * Conversions from string types to floating-point types.
1117 ******************************************************************************/
1120 } // namespace detail
1123 * StringPiece to bool, with progress information. Alters the
1124 * StringPiece parameter to munch the already-parsed characters.
1126 inline void parseTo(StringPiece* src, bool& out) {
1127 out = detail::str_to_bool(src);
1131 * Parsing strings to numeric types. These routines differ from
1132 * parseTo(str, numeric) routines in that they take a POINTER TO a StringPiece
1133 * and alter that StringPiece to reflect progress information.
1135 template <class Tgt>
1136 typename std::enable_if<
1137 std::is_integral<typename std::remove_cv<Tgt>::type>::value>::type
1138 parseTo(StringPiece* src, Tgt& out) {
1139 out = detail::str_to_integral<Tgt>(src);
1142 inline void parseTo(StringPiece* src, float& out) {
1143 out = detail::str_to_float(src);
1146 inline void parseTo(StringPiece* src, double& out) {
1147 out = detail::str_to_double(src);
1150 template <class Tgt>
1151 typename std::enable_if<
1152 std::is_floating_point<Tgt>::value ||
1153 std::is_integral<typename std::remove_cv<Tgt>::type>::value>::type
1154 parseTo(StringPiece src, Tgt& out) {
1156 detail::enforceWhitespace(src);
1159 /*******************************************************************************
1160 * Integral to floating point and back
1161 ******************************************************************************/
1164 * Checked conversion from integral to floating point and back. The
1165 * result must be convertible back to the source type without loss of
1166 * precision. This seems Draconian but sometimes is what's needed, and
1167 * complements existing routines nicely. For various rounding
1168 * routines, see <math>.
1170 template <class Tgt, class Src>
1171 typename std::enable_if<
1172 (std::is_integral<Src>::value && std::is_floating_point<Tgt>::value)
1174 (std::is_floating_point<Src>::value && std::is_integral<Tgt>::value),
1176 to(const Src & value) {
1177 Tgt result = Tgt(value);
1178 auto witness = static_cast<Src>(result);
1179 if (value != witness) {
1180 throw std::range_error(
1181 to<std::string>("to<>: loss of precision when converting ", value,
1182 #ifdef FOLLY_HAS_RTTI
1183 " to type ", typeid(Tgt).name()
1192 /*******************************************************************************
1193 * Custom Conversions
1195 * Any type can be used with folly::to by implementing parseTo. The
1196 * implementation should be provided in the namespace of the type to facilitate
1197 * argument-dependent lookup:
1199 * namespace other_namespace {
1200 * void parseTo(::folly::StringPiece, OtherType&);
1202 ******************************************************************************/
1204 typename std::enable_if<std::is_enum<T>::value>::type
1205 parseTo(StringPiece in, T& out) {
1206 typename std::underlying_type<T>::type tmp;
1208 out = static_cast<T>(tmp);
1211 inline void parseTo(StringPiece in, StringPiece& out) {
1215 inline void parseTo(StringPiece in, std::string& out) {
1217 out.append(in.data(), in.size());
1220 inline void parseTo(StringPiece in, fbstring& out) {
1222 out.append(in.data(), in.size());
1226 * String or StringPiece to target conversion. Accepts leading and trailing
1227 * whitespace, but no non-space trailing characters.
1230 template <class Tgt>
1231 typename std::enable_if<!std::is_same<StringPiece, Tgt>::value, Tgt>::type
1232 to(StringPiece src) {
1234 parseTo(src, result);
1238 template <class Tgt>
1239 Tgt to(StringPiece* src) {
1241 parseTo(src, result);
1245 /*******************************************************************************
1246 * Enum to anything and back
1247 ******************************************************************************/
1249 template <class Tgt, class Src>
1250 typename std::enable_if<
1251 std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value, Tgt>::type
1252 to(const Src & value) {
1253 return to<Tgt>(static_cast<typename std::underlying_type<Src>::type>(value));
1256 template <class Tgt, class Src>
1257 typename std::enable_if<
1258 std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value, Tgt>::type
1259 to(const Src & value) {
1260 return static_cast<Tgt>(to<typename std::underlying_type<Tgt>::type>(value));
1263 } // namespace folly
1265 // FOLLY_CONV_INTERNAL is defined by Conv.cpp. Keep the FOLLY_RANGE_CHECK
1266 // macro for use in Conv.cpp, but #undefine it everywhere else we are included,
1267 // to avoid defining this global macro name in other files that include Conv.h.
1268 #ifndef FOLLY_CONV_INTERNAL
1269 #undef FOLLY_RANGE_CHECK
1270 #undef FOLLY_RANGE_CHECK_BEGIN_END
1271 #undef FOLLY_RANGE_CHECK_STRINGPIECE
1272 #undef FOLLY_RANGE_CHECK_STRINGIZE
1273 #undef FOLLY_RANGE_CHECK_STRINGIZE2