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/*
* Copyright 2017 Facebook, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/**
* Converts anything to anything, with an emphasis on performance and
* safety.
*
* @author Andrei Alexandrescu (andrei.alexandrescu@fb.com)
*/
#pragma once
#include <algorithm>
#include <cctype>
#include <climits>
#include <cstddef>
#include <limits>
#include <stdexcept>
#include <string>
#include <tuple>
#include <type_traits>
#include <typeinfo>
#include <utility>
#include <boost/implicit_cast.hpp>
#include <double-conversion/double-conversion.h> // V8 JavaScript implementation
#include <folly/Demangle.h>
#include <folly/Expected.h>
#include <folly/FBString.h>
#include <folly/Likely.h>
#include <folly/Range.h>
#include <folly/Traits.h>
#include <folly/Unit.h>
#include <folly/portability/Math.h>
namespace folly {
// Keep this in sync with kErrorStrings in Conv.cpp
enum class ConversionCode : unsigned char {
SUCCESS,
EMPTY_INPUT_STRING,
NO_DIGITS,
BOOL_OVERFLOW,
BOOL_INVALID_VALUE,
NON_DIGIT_CHAR,
INVALID_LEADING_CHAR,
POSITIVE_OVERFLOW,
NEGATIVE_OVERFLOW,
STRING_TO_FLOAT_ERROR,
NON_WHITESPACE_AFTER_END,
ARITH_POSITIVE_OVERFLOW,
ARITH_NEGATIVE_OVERFLOW,
ARITH_LOSS_OF_PRECISION,
NUM_ERROR_CODES, // has to be the last entry
};
struct ConversionErrorBase : std::range_error {
using std::range_error::range_error;
};
class ConversionError : public ConversionErrorBase {
public:
ConversionError(const std::string& str, ConversionCode code)
: ConversionErrorBase(str), code_(code) {}
ConversionError(const char* str, ConversionCode code)
: ConversionErrorBase(str), code_(code) {}
ConversionCode errorCode() const {
return code_;
}
private:
ConversionCode code_;
};
/*******************************************************************************
* Custom Error Translation
*
* Your overloaded parseTo() function can return a custom error code on failure.
* ::folly::to() will call makeConversionError to translate that error code into
* an object to throw. makeConversionError is found by argument-dependent
* lookup. It should have this signature:
*
* namespace other_namespace {
* enum YourErrorCode { BAD_ERROR, WORSE_ERROR };
*
* struct YourConversionError : ConversionErrorBase {
* YourConversionError(const char* what) : ConversionErrorBase(what) {}
* };
*
* YourConversionError
* makeConversionError(YourErrorCode code, ::folly::StringPiece sp) {
* ...
* return YourConversionError(messageString);
* }
******************************************************************************/
ConversionError makeConversionError(ConversionCode code, StringPiece sp);
namespace detail {
/**
* Enforce that the suffix following a number is made up only of whitespace.
*/
inline ConversionCode enforceWhitespaceErr(StringPiece sp) {
for (auto c : sp) {
if (UNLIKELY(!std::isspace(c))) {
return ConversionCode::NON_WHITESPACE_AFTER_END;
}
}
return ConversionCode::SUCCESS;
}
/**
* Keep this implementation around for prettyToDouble().
*/
inline void enforceWhitespace(StringPiece sp) {
auto err = enforceWhitespaceErr(sp);
if (err != ConversionCode::SUCCESS) {
throw makeConversionError(err, sp);
}
}
}
/**
* The identity conversion function.
* tryTo<T>(T) returns itself for all types T.
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_same<Tgt, typename std::decay<Src>::type>::value,
Expected<Tgt, ConversionCode>>::type
tryTo(Src&& value) {
return std::forward<Src>(value);
}
template <class Tgt, class Src>
typename std::enable_if<
std::is_same<Tgt, typename std::decay<Src>::type>::value,
Tgt>::type
to(Src&& value) {
return std::forward<Src>(value);
}
/*******************************************************************************
* Arithmetic to boolean
******************************************************************************/
/**
* Unchecked conversion from arithmetic to boolean. This is different from the
* other arithmetic conversions because we use the C convention of treating any
* non-zero value as true, instead of range checking.
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_arithmetic<Src>::value && !std::is_same<Tgt, Src>::value &&
std::is_same<Tgt, bool>::value,
Expected<Tgt, ConversionCode>>::type
tryTo(const Src& value) {
return value != Src();
}
template <class Tgt, class Src>
typename std::enable_if<
std::is_arithmetic<Src>::value && !std::is_same<Tgt, Src>::value &&
std::is_same<Tgt, bool>::value,
Tgt>::type
to(const Src& value) {
return value != Src();
}
/*******************************************************************************
* Anything to string
******************************************************************************/
namespace detail {
#ifdef _MSC_VER
// MSVC can't quite figure out the LastElementImpl::call() stuff
// in the base implementation, so we have to use tuples instead,
// which result in significantly more templates being compiled,
// though the runtime performance is the same.
template <typename... Ts>
auto getLastElement(Ts&&... ts) -> decltype(
std::get<sizeof...(Ts)-1>(std::forward_as_tuple(std::forward<Ts>(ts)...))) {
return std::get<sizeof...(Ts)-1>(
std::forward_as_tuple(std::forward<Ts>(ts)...));
}
inline void getLastElement() {}
template <size_t size, typename... Ts>
struct LastElementType : std::tuple_element<size - 1, std::tuple<Ts...>> {};
template <>
struct LastElementType<0> {
using type = void;
};
template <class... Ts>
struct LastElement
: std::decay<typename LastElementType<sizeof...(Ts), Ts...>::type> {};
#else
template <typename... Ts>
struct LastElementImpl {
static void call(Ignored<Ts>...) {}
};
template <typename Head, typename... Ts>
struct LastElementImpl<Head, Ts...> {
template <typename Last>
static Last call(Ignored<Ts>..., Last&& last) {
return std::forward<Last>(last);
}
};
template <typename... Ts>
auto getLastElement(const Ts&... ts)
-> decltype(LastElementImpl<Ts...>::call(ts...)) {
return LastElementImpl<Ts...>::call(ts...);
}
template <class... Ts>
struct LastElement : std::decay<decltype(
LastElementImpl<Ts...>::call(std::declval<Ts>()...))> {
};
#endif
} // namespace detail
/*******************************************************************************
* Conversions from integral types to string types.
******************************************************************************/
#if FOLLY_HAVE_INT128_T
namespace detail {
template <typename IntegerType>
constexpr unsigned int
digitsEnough() {
return (unsigned int)(ceil(sizeof(IntegerType) * CHAR_BIT * M_LN2 / M_LN10));
}
inline size_t
unsafeTelescope128(char * buffer, size_t room, unsigned __int128 x) {
typedef unsigned __int128 Usrc;
size_t p = room - 1;
while (x >= (Usrc(1) << 64)) { // Using 128-bit division while needed
const auto y = x / 10;
const auto digit = x % 10;
buffer[p--] = '0' + digit;
x = y;
}
uint64_t xx = x; // Moving to faster 64-bit division thereafter
while (xx >= 10) {
const auto y = xx / 10ULL;
const auto digit = xx % 10ULL;
buffer[p--] = '0' + digit;
xx = y;
}
buffer[p] = '0' + xx;
return p;
}
}
#endif
/**
* Returns the number of digits in the base 10 representation of an
* uint64_t. Useful for preallocating buffers and such. It's also used
* internally, see below. Measurements suggest that defining a
* separate overload for 32-bit integers is not worthwhile.
*/
inline uint32_t digits10(uint64_t v) {
#ifdef __x86_64__
// For this arch we can get a little help from specialized CPU instructions
// which can count leading zeroes; 64 minus that is appx. log (base 2).
// Use that to approximate base-10 digits (log_10) and then adjust if needed.
// 10^i, defined for i 0 through 19.
// This is 20 * 8 == 160 bytes, which fits neatly into 5 cache lines
// (assuming a cache line size of 64).
static const uint64_t powersOf10[20] FOLLY_ALIGNED(64) = {
1,
10,
100,
1000,
10000,
100000,
1000000,
10000000,
100000000,
1000000000,
10000000000,
100000000000,
1000000000000,
10000000000000,
100000000000000,
1000000000000000,
10000000000000000,
100000000000000000,
1000000000000000000,
10000000000000000000UL,
};
// "count leading zeroes" operation not valid; for 0; special case this.
if UNLIKELY (! v) {
return 1;
}
// bits is in the ballpark of log_2(v).
const uint8_t leadingZeroes = __builtin_clzll(v);
const auto bits = 63 - leadingZeroes;
// approximate log_10(v) == log_10(2) * bits.
// Integer magic below: 77/256 is appx. 0.3010 (log_10(2)).
// The +1 is to make this the ceiling of the log_10 estimate.
const uint32_t minLength = 1 + ((bits * 77) >> 8);
// return that log_10 lower bound, plus adjust if input >= 10^(that bound)
// in case there's a small error and we misjudged length.
return minLength + (uint32_t) (UNLIKELY (v >= powersOf10[minLength]));
#else
uint32_t result = 1;
for (;;) {
if (LIKELY(v < 10)) return result;
if (LIKELY(v < 100)) return result + 1;
if (LIKELY(v < 1000)) return result + 2;
if (LIKELY(v < 10000)) return result + 3;
// Skip ahead by 4 orders of magnitude
v /= 10000U;
result += 4;
}
#endif
}
/**
* Copies the ASCII base 10 representation of v into buffer and
* returns the number of bytes written. Does NOT append a \0. Assumes
* the buffer points to digits10(v) bytes of valid memory. Note that
* uint64 needs at most 20 bytes, uint32_t needs at most 10 bytes,
* uint16_t needs at most 5 bytes, and so on. Measurements suggest
* that defining a separate overload for 32-bit integers is not
* worthwhile.
*
* This primitive is unsafe because it makes the size assumption and
* because it does not add a terminating \0.
*/
inline uint32_t uint64ToBufferUnsafe(uint64_t v, char *const buffer) {
auto const result = digits10(v);
// WARNING: using size_t or pointer arithmetic for pos slows down
// the loop below 20x. This is because several 32-bit ops can be
// done in parallel, but only fewer 64-bit ones.
uint32_t pos = result - 1;
while (v >= 10) {
// Keep these together so a peephole optimization "sees" them and
// computes them in one shot.
auto const q = v / 10;
auto const r = static_cast<char>(v % 10);
buffer[pos--] = '0' + r;
v = q;
}
// Last digit is trivial to handle
buffer[pos] = static_cast<char>(v) + '0';
return result;
}
/**
* A single char gets appended.
*/
template <class Tgt>
void toAppend(char value, Tgt * result) {
*result += value;
}
template<class T>
constexpr typename std::enable_if<
std::is_same<T, char>::value,
size_t>::type
estimateSpaceNeeded(T) {
return 1;
}
/**
* Everything implicitly convertible to const char* gets appended.
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_convertible<Src, const char*>::value
&& IsSomeString<Tgt>::value>::type
toAppend(Src value, Tgt * result) {
// Treat null pointers like an empty string, as in:
// operator<<(std::ostream&, const char*).
const char* c = value;
if (c) {
result->append(value);
}
}
template <class Src>
typename std::enable_if<std::is_convertible<Src, const char*>::value, size_t>::
type
estimateSpaceNeeded(Src value) {
const char *c = value;
if (c) {
return folly::StringPiece(value).size();
};
return 0;
}
template<class Src>
typename std::enable_if<
(std::is_convertible<Src, folly::StringPiece>::value ||
IsSomeString<Src>::value) &&
!std::is_convertible<Src, const char*>::value,
size_t>::type
estimateSpaceNeeded(Src value) {
return folly::StringPiece(value).size();
}
template <>
inline size_t estimateSpaceNeeded(std::nullptr_t /* value */) {
return 0;
}
template<class Src>
typename std::enable_if<
std::is_pointer<Src>::value &&
IsSomeString<std::remove_pointer<Src>>::value,
size_t>::type
estimateSpaceNeeded(Src value) {
return value->size();
}
/**
* Strings get appended, too.
*/
template <class Tgt, class Src>
typename std::enable_if<
IsSomeString<Src>::value && IsSomeString<Tgt>::value>::type
toAppend(const Src& value, Tgt * result) {
result->append(value);
}
/**
* and StringPiece objects too
*/
template <class Tgt>
typename std::enable_if<
IsSomeString<Tgt>::value>::type
toAppend(StringPiece value, Tgt * result) {
result->append(value.data(), value.size());
}
/**
* There's no implicit conversion from fbstring to other string types,
* so make a specialization.
*/
template <class Tgt>
typename std::enable_if<
IsSomeString<Tgt>::value>::type
toAppend(const fbstring& value, Tgt * result) {
result->append(value.data(), value.size());
}
#if FOLLY_HAVE_INT128_T
/**
* Special handling for 128 bit integers.
*/
template <class Tgt>
void
toAppend(__int128 value, Tgt * result) {
typedef unsigned __int128 Usrc;
char buffer[detail::digitsEnough<unsigned __int128>() + 1];
size_t p;
if (value < 0) {
p = detail::unsafeTelescope128(buffer, sizeof(buffer), -Usrc(value));
buffer[--p] = '-';
} else {
p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
}
result->append(buffer + p, buffer + sizeof(buffer));
}
template <class Tgt>
void
toAppend(unsigned __int128 value, Tgt * result) {
char buffer[detail::digitsEnough<unsigned __int128>()];
size_t p;
p = detail::unsafeTelescope128(buffer, sizeof(buffer), value);
result->append(buffer + p, buffer + sizeof(buffer));
}
template<class T>
constexpr typename std::enable_if<
std::is_same<T, __int128>::value,
size_t>::type
estimateSpaceNeeded(T) {
return detail::digitsEnough<__int128>();
}
template<class T>
constexpr typename std::enable_if<
std::is_same<T, unsigned __int128>::value,
size_t>::type
estimateSpaceNeeded(T) {
return detail::digitsEnough<unsigned __int128>();
}
#endif
/**
* int32_t and int64_t to string (by appending) go through here. The
* result is APPENDED to a preexisting string passed as the second
* parameter. This should be efficient with fbstring because fbstring
* incurs no dynamic allocation below 23 bytes and no number has more
* than 22 bytes in its textual representation (20 for digits, one for
* sign, one for the terminating 0).
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_integral<Src>::value && std::is_signed<Src>::value &&
IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
toAppend(Src value, Tgt * result) {
char buffer[20];
if (value < 0) {
result->push_back('-');
result->append(
buffer,
uint64ToBufferUnsafe(~static_cast<uint64_t>(value) + 1, buffer));
} else {
result->append(buffer, uint64ToBufferUnsafe(uint64_t(value), buffer));
}
}
template <class Src>
typename std::enable_if<
std::is_integral<Src>::value && std::is_signed<Src>::value
&& sizeof(Src) >= 4 && sizeof(Src) < 16,
size_t>::type
estimateSpaceNeeded(Src value) {
if (value < 0) {
// When "value" is the smallest negative, negating it would evoke
// undefined behavior, so, instead of writing "-value" below, we write
// "~static_cast<uint64_t>(value) + 1"
return 1 + digits10(~static_cast<uint64_t>(value) + 1);
}
return digits10(static_cast<uint64_t>(value));
}
/**
* As above, but for uint32_t and uint64_t.
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_integral<Src>::value && !std::is_signed<Src>::value
&& IsSomeString<Tgt>::value && sizeof(Src) >= 4>::type
toAppend(Src value, Tgt * result) {
char buffer[20];
result->append(buffer, uint64ToBufferUnsafe(value, buffer));
}
template <class Src>
typename std::enable_if<
std::is_integral<Src>::value && !std::is_signed<Src>::value
&& sizeof(Src) >= 4 && sizeof(Src) < 16,
size_t>::type
estimateSpaceNeeded(Src value) {
return digits10(value);
}
/**
* All small signed and unsigned integers to string go through 32-bit
* types int32_t and uint32_t, respectively.
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_integral<Src>::value
&& IsSomeString<Tgt>::value && sizeof(Src) < 4>::type
toAppend(Src value, Tgt * result) {
typedef typename
std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
Intermediate;
toAppend<Tgt>(static_cast<Intermediate>(value), result);
}
template <class Src>
typename std::enable_if<
std::is_integral<Src>::value
&& sizeof(Src) < 4
&& !std::is_same<Src, char>::value,
size_t>::type
estimateSpaceNeeded(Src value) {
typedef typename
std::conditional<std::is_signed<Src>::value, int64_t, uint64_t>::type
Intermediate;
return estimateSpaceNeeded(static_cast<Intermediate>(value));
}
/**
* Enumerated values get appended as integers.
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_enum<Src>::value && IsSomeString<Tgt>::value>::type
toAppend(Src value, Tgt * result) {
toAppend(
static_cast<typename std::underlying_type<Src>::type>(value), result);
}
template <class Src>
typename std::enable_if<
std::is_enum<Src>::value, size_t>::type
estimateSpaceNeeded(Src value) {
return estimateSpaceNeeded(
static_cast<typename std::underlying_type<Src>::type>(value));
}
/*******************************************************************************
* Conversions from floating-point types to string types.
******************************************************************************/
namespace detail {
constexpr int kConvMaxDecimalInShortestLow = -6;
constexpr int kConvMaxDecimalInShortestHigh = 21;
} // folly::detail
/** Wrapper around DoubleToStringConverter **/
template <class Tgt, class Src>
typename std::enable_if<
std::is_floating_point<Src>::value
&& IsSomeString<Tgt>::value>::type
toAppend(
Src value,
Tgt * result,
double_conversion::DoubleToStringConverter::DtoaMode mode,
unsigned int numDigits) {
using namespace double_conversion;
DoubleToStringConverter
conv(DoubleToStringConverter::NO_FLAGS,
"Infinity", "NaN", 'E',
detail::kConvMaxDecimalInShortestLow,
detail::kConvMaxDecimalInShortestHigh,
6, // max leading padding zeros
1); // max trailing padding zeros
char buffer[256];
StringBuilder builder(buffer, sizeof(buffer));
switch (mode) {
case DoubleToStringConverter::SHORTEST:
conv.ToShortest(value, &builder);
break;
case DoubleToStringConverter::FIXED:
conv.ToFixed(value, int(numDigits), &builder);
break;
default:
CHECK(mode == DoubleToStringConverter::PRECISION);
conv.ToPrecision(value, int(numDigits), &builder);
break;
}
const size_t length = size_t(builder.position());
builder.Finalize();
result->append(buffer, length);
}
/**
* As above, but for floating point
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_floating_point<Src>::value
&& IsSomeString<Tgt>::value>::type
toAppend(Src value, Tgt * result) {
toAppend(
value, result, double_conversion::DoubleToStringConverter::SHORTEST, 0);
}
/**
* Upper bound of the length of the output from
* DoubleToStringConverter::ToShortest(double, StringBuilder*),
* as used in toAppend(double, string*).
*/
template <class Src>
typename std::enable_if<
std::is_floating_point<Src>::value, size_t>::type
estimateSpaceNeeded(Src value) {
// kBase10MaximalLength is 17. We add 1 for decimal point,
// e.g. 10.0/9 is 17 digits and 18 characters, including the decimal point.
constexpr int kMaxMantissaSpace =
double_conversion::DoubleToStringConverter::kBase10MaximalLength + 1;
// strlen("E-") + digits10(numeric_limits<double>::max_exponent10)
constexpr int kMaxExponentSpace = 2 + 3;
static const int kMaxPositiveSpace = std::max({
// E.g. 1.1111111111111111E-100.
kMaxMantissaSpace + kMaxExponentSpace,
// E.g. 0.000001.1111111111111111, if kConvMaxDecimalInShortestLow is -6.
kMaxMantissaSpace - detail::kConvMaxDecimalInShortestLow,
// If kConvMaxDecimalInShortestHigh is 21, then 1e21 is the smallest
// number > 1 which ToShortest outputs in exponential notation,
// so 21 is the longest non-exponential number > 1.
detail::kConvMaxDecimalInShortestHigh
});
return size_t(
kMaxPositiveSpace +
(value < 0 ? 1 : 0)); // +1 for minus sign, if negative
}
/**
* This can be specialized, together with adding specialization
* for estimateSpaceNeed for your type, so that we allocate
* as much as you need instead of the default
*/
template<class Src>
struct HasLengthEstimator : std::false_type {};
template <class Src>
constexpr typename std::enable_if<
!std::is_fundamental<Src>::value
#if FOLLY_HAVE_INT128_T
// On OSX 10.10, is_fundamental<__int128> is false :-O
&& !std::is_same<__int128, Src>::value
&& !std::is_same<unsigned __int128, Src>::value
#endif
&& !IsSomeString<Src>::value
&& !std::is_convertible<Src, const char*>::value
&& !std::is_convertible<Src, StringPiece>::value
&& !std::is_enum<Src>::value
&& !HasLengthEstimator<Src>::value,
size_t>::type
estimateSpaceNeeded(const Src&) {
return sizeof(Src) + 1; // dumbest best effort ever?
}
namespace detail {
template <class Tgt>
typename std::enable_if<IsSomeString<Tgt>::value, size_t>::type
estimateSpaceToReserve(size_t sofar, Tgt*) {
return sofar;
}
template <class T, class... Ts>
size_t estimateSpaceToReserve(size_t sofar, const T& v, const Ts&... vs) {
return estimateSpaceToReserve(sofar + estimateSpaceNeeded(v), vs...);
}
template<class...Ts>
void reserveInTarget(const Ts&...vs) {
getLastElement(vs...)->reserve(estimateSpaceToReserve(0, vs...));
}
template<class Delimiter, class...Ts>
void reserveInTargetDelim(const Delimiter& d, const Ts&...vs) {
static_assert(sizeof...(vs) >= 2, "Needs at least 2 args");
size_t fordelim = (sizeof...(vs) - 2) *
estimateSpaceToReserve(0, d, static_cast<std::string*>(nullptr));
getLastElement(vs...)->reserve(estimateSpaceToReserve(fordelim, vs...));
}
/**
* Variadic base case: append one element
*/
template <class T, class Tgt>
typename std::enable_if<
IsSomeString<typename std::remove_pointer<Tgt>::type>
::value>::type
toAppendStrImpl(const T& v, Tgt result) {
toAppend(v, result);
}
template <class T, class... Ts>
typename std::enable_if<
sizeof...(Ts) >= 2 &&
IsSomeString<typename std::remove_pointer<
typename detail::LastElement<const Ts&...>::type>::type>::value>::type
toAppendStrImpl(const T& v, const Ts&... vs) {
toAppend(v, getLastElement(vs...));
toAppendStrImpl(vs...);
}
template <class Delimiter, class T, class Tgt>
typename std::enable_if<
IsSomeString<typename std::remove_pointer<Tgt>::type>::value>::type
toAppendDelimStrImpl(const Delimiter& /* delim */, const T& v, Tgt result) {
toAppend(v, result);
}
template <class Delimiter, class T, class... Ts>
typename std::enable_if<
sizeof...(Ts) >= 2 &&
IsSomeString<typename std::remove_pointer<
typename detail::LastElement<const Ts&...>::type>::type>::value>::type
toAppendDelimStrImpl(const Delimiter& delim, const T& v, const Ts&... vs) {
// we are really careful here, calling toAppend with just one element does
// not try to estimate space needed (as we already did that). If we call
// toAppend(v, delim, ....) we would do unnecesary size calculation
toAppend(v, detail::getLastElement(vs...));
toAppend(delim, detail::getLastElement(vs...));
toAppendDelimStrImpl(delim, vs...);
}
} // folly::detail
/**
* Variadic conversion to string. Appends each element in turn.
* If we have two or more things to append, we it will not reserve
* the space for them and will depend on strings exponential growth.
* If you just append once consider using toAppendFit which reserves
* the space needed (but does not have exponential as a result).
*
* Custom implementations of toAppend() can be provided in the same namespace as
* the type to customize printing. estimateSpaceNeed() may also be provided to
* avoid reallocations in toAppendFit():
*
* namespace other_namespace {
*
* template <class String>
* void toAppend(const OtherType&, String* out);
*
* // optional
* size_t estimateSpaceNeeded(const OtherType&);
*
* }
*/
template <class... Ts>
typename std::enable_if<
sizeof...(Ts) >= 3 &&
IsSomeString<typename std::remove_pointer<
typename detail::LastElement<const Ts&...>::type>::type>::value>::type
toAppend(const Ts&... vs) {
::folly::detail::toAppendStrImpl(vs...);
}
#ifdef _MSC_VER
// Special case pid_t on MSVC, because it's a void* rather than an
// integral type. We can't do a global special case because this is already
// dangerous enough (as most pointers will implicitly convert to a void*)
// just doing it for MSVC.
template <class Tgt>
void toAppend(const pid_t a, Tgt* res) {
toAppend(uint64_t(a), res);
}
#endif
/**
* Special version of the call that preallocates exaclty as much memory
* as need for arguments to be stored in target. This means we are
* not doing exponential growth when we append. If you are using it
* in a loop you are aiming at your foot with a big perf-destroying
* bazooka.
* On the other hand if you are appending to a string once, this
* will probably save a few calls to malloc.
*/
template <class... Ts>
typename std::enable_if<IsSomeString<typename std::remove_pointer<
typename detail::LastElement<const Ts&...>::type>::type>::value>::type
toAppendFit(const Ts&... vs) {
::folly::detail::reserveInTarget(vs...);
toAppend(vs...);
}
template <class Ts>
void toAppendFit(const Ts&) {}
/**
* Variadic base case: do nothing.
*/
template <class Tgt>
typename std::enable_if<IsSomeString<Tgt>::value>::type toAppend(
Tgt* /* result */) {}
/**
* Variadic base case: do nothing.
*/
template <class Delimiter, class Tgt>
typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
const Delimiter& /* delim */, Tgt* /* result */) {}
/**
* 1 element: same as toAppend.
*/
template <class Delimiter, class T, class Tgt>
typename std::enable_if<IsSomeString<Tgt>::value>::type toAppendDelim(
const Delimiter& /* delim */, const T& v, Tgt* tgt) {
toAppend(v, tgt);
}
/**
* Append to string with a delimiter in between elements. Check out
* comments for toAppend for details about memory allocation.
*/
template <class Delimiter, class... Ts>
typename std::enable_if<
sizeof...(Ts) >= 3 &&
IsSomeString<typename std::remove_pointer<
typename detail::LastElement<const Ts&...>::type>::type>::value>::type
toAppendDelim(const Delimiter& delim, const Ts&... vs) {
detail::toAppendDelimStrImpl(delim, vs...);
}
/**
* Detail in comment for toAppendFit
*/
template <class Delimiter, class... Ts>
typename std::enable_if<IsSomeString<typename std::remove_pointer<
typename detail::LastElement<const Ts&...>::type>::type>::value>::type
toAppendDelimFit(const Delimiter& delim, const Ts&... vs) {
detail::reserveInTargetDelim(delim, vs...);
toAppendDelim(delim, vs...);
}
template <class De, class Ts>
void toAppendDelimFit(const De&, const Ts&) {}
/**
* to<SomeString>(v1, v2, ...) uses toAppend() (see below) as back-end
* for all types.
*/
template <class Tgt, class... Ts>
typename std::enable_if<
IsSomeString<Tgt>::value &&
(sizeof...(Ts) != 1 ||
!std::is_same<Tgt, typename detail::LastElement<const Ts&...>::type>::
value),
Tgt>::type
to(const Ts&... vs) {
Tgt result;
toAppendFit(vs..., &result);
return result;
}
/**
* Special version of to<SomeString> for floating point. When calling
* folly::to<SomeString>(double), generic implementation above will
* firstly reserve 24 (or 25 when negative value) bytes. This will
* introduce a malloc call for most mainstream string implementations.
*
* But for most cases, a floating point doesn't need 24 (or 25) bytes to
* be converted as a string.
*
* This special version will not do string reserve.
*/
template <class Tgt, class Src>
typename std::enable_if<
IsSomeString<Tgt>::value && std::is_floating_point<Src>::value,
Tgt>::type
to(Src value) {
Tgt result;
toAppend(value, &result);
return result;
}
/**
* toDelim<SomeString>(SomeString str) returns itself.
*/
template <class Tgt, class Delim, class Src>
typename std::enable_if<IsSomeString<Tgt>::value &&
std::is_same<Tgt, Src>::value,
Tgt>::type
toDelim(const Delim& /* delim */, const Src& value) {
return value;
}
/**
* toDelim<SomeString>(delim, v1, v2, ...) uses toAppendDelim() as
* back-end for all types.
*/
template <class Tgt, class Delim, class... Ts>
typename std::enable_if<
IsSomeString<Tgt>::value &&
(sizeof...(Ts) != 1 ||
!std::is_same<Tgt, typename detail::LastElement<const Ts&...>::type>::
value),
Tgt>::type
toDelim(const Delim& delim, const Ts&... vs) {
Tgt result;
toAppendDelimFit(delim, vs..., &result);
return result;
}
/*******************************************************************************
* Conversions from string types to integral types.
******************************************************************************/
namespace detail {
Expected<bool, ConversionCode> str_to_bool(StringPiece* src) noexcept;
template <typename T>
Expected<T, ConversionCode> str_to_floating(StringPiece* src) noexcept;
extern template Expected<float, ConversionCode> str_to_floating<float>(
StringPiece* src) noexcept;
extern template Expected<double, ConversionCode> str_to_floating<double>(
StringPiece* src) noexcept;
template <class Tgt>
Expected<Tgt, ConversionCode> digits_to(const char* b, const char* e) noexcept;
extern template Expected<char, ConversionCode> digits_to<char>(
const char*,
const char*) noexcept;
extern template Expected<signed char, ConversionCode> digits_to<signed char>(
const char*,
const char*) noexcept;
extern template Expected<unsigned char, ConversionCode>
digits_to<unsigned char>(const char*, const char*) noexcept;
extern template Expected<short, ConversionCode> digits_to<short>(
const char*,
const char*) noexcept;
extern template Expected<unsigned short, ConversionCode>
digits_to<unsigned short>(const char*, const char*) noexcept;
extern template Expected<int, ConversionCode> digits_to<int>(
const char*,
const char*) noexcept;
extern template Expected<unsigned int, ConversionCode> digits_to<unsigned int>(
const char*,
const char*) noexcept;
extern template Expected<long, ConversionCode> digits_to<long>(
const char*,
const char*) noexcept;
extern template Expected<unsigned long, ConversionCode>
digits_to<unsigned long>(const char*, const char*) noexcept;
extern template Expected<long long, ConversionCode> digits_to<long long>(
const char*,
const char*) noexcept;
extern template Expected<unsigned long long, ConversionCode>
digits_to<unsigned long long>(const char*, const char*) noexcept;
#if FOLLY_HAVE_INT128_T
extern template Expected<__int128, ConversionCode> digits_to<__int128>(
const char*,
const char*) noexcept;
extern template Expected<unsigned __int128, ConversionCode>
digits_to<unsigned __int128>(const char*, const char*) noexcept;
#endif
template <class T>
Expected<T, ConversionCode> str_to_integral(StringPiece* src) noexcept;
extern template Expected<char, ConversionCode> str_to_integral<char>(
StringPiece* src) noexcept;
extern template Expected<signed char, ConversionCode>
str_to_integral<signed char>(StringPiece* src) noexcept;
extern template Expected<unsigned char, ConversionCode>
str_to_integral<unsigned char>(StringPiece* src) noexcept;
extern template Expected<short, ConversionCode> str_to_integral<short>(
StringPiece* src) noexcept;
extern template Expected<unsigned short, ConversionCode>
str_to_integral<unsigned short>(StringPiece* src) noexcept;
extern template Expected<int, ConversionCode> str_to_integral<int>(
StringPiece* src) noexcept;
extern template Expected<unsigned int, ConversionCode>
str_to_integral<unsigned int>(StringPiece* src) noexcept;
extern template Expected<long, ConversionCode> str_to_integral<long>(
StringPiece* src) noexcept;
extern template Expected<unsigned long, ConversionCode>
str_to_integral<unsigned long>(StringPiece* src) noexcept;
extern template Expected<long long, ConversionCode> str_to_integral<long long>(
StringPiece* src) noexcept;
extern template Expected<unsigned long long, ConversionCode>
str_to_integral<unsigned long long>(StringPiece* src) noexcept;
#if FOLLY_HAVE_INT128_T
extern template Expected<__int128, ConversionCode> str_to_integral<__int128>(
StringPiece* src) noexcept;
extern template Expected<unsigned __int128, ConversionCode>
str_to_integral<unsigned __int128>(StringPiece* src) noexcept;
#endif
template <typename T>
typename std::
enable_if<std::is_same<T, bool>::value, Expected<T, ConversionCode>>::type
convertTo(StringPiece* src) noexcept {
return str_to_bool(src);
}
template <typename T>
typename std::enable_if<
std::is_floating_point<T>::value,
Expected<T, ConversionCode>>::type
convertTo(StringPiece* src) noexcept {
return str_to_floating<T>(src);
}
template <typename T>
typename std::enable_if<
std::is_integral<T>::value && !std::is_same<T, bool>::value,
Expected<T, ConversionCode>>::type
convertTo(StringPiece* src) noexcept {
return str_to_integral<T>(src);
}
} // namespace detail
/**
* String represented as a pair of pointers to char to unsigned
* integrals. Assumes NO whitespace before or after.
*/
template <typename Tgt>
typename std::enable_if<
std::is_integral<Tgt>::value && !std::is_same<Tgt, bool>::value,
Expected<Tgt, ConversionCode>>::type
tryTo(const char* b, const char* e) {
return detail::digits_to<Tgt>(b, e);
}
template <typename Tgt>
typename std::enable_if<
std::is_integral<Tgt>::value && !std::is_same<Tgt, bool>::value,
Tgt>::type
to(const char* b, const char* e) {
return tryTo<Tgt>(b, e).thenOrThrow(
[](Tgt res) { return res; },
[=](ConversionCode code) {
return makeConversionError(code, StringPiece(b, e));
});
}
/*******************************************************************************
* Conversions from string types to arithmetic types.
******************************************************************************/
/**
* Parsing strings to numeric types.
*/
template <typename Tgt>
FOLLY_WARN_UNUSED_RESULT inline typename std::enable_if<
std::is_arithmetic<Tgt>::value,
Expected<StringPiece, ConversionCode>>::type
parseTo(StringPiece src, Tgt& out) {
return detail::convertTo<Tgt>(&src).then(
[&](Tgt res) { return void(out = res), src; });
}
/*******************************************************************************
* Integral / Floating Point to integral / Floating Point
******************************************************************************/
namespace detail {
/**
* Bool to integral/float doesn't need any special checks, and this
* overload means we aren't trying to see if a bool is less than
* an integer.
*/
template <class Tgt>
typename std::enable_if<
!std::is_same<Tgt, bool>::value &&
(std::is_integral<Tgt>::value || std::is_floating_point<Tgt>::value),
Expected<Tgt, ConversionCode>>::type
convertTo(const bool& value) noexcept {
return static_cast<Tgt>(value ? 1 : 0);
}
/**
* Checked conversion from integral to integral. The checks are only
* performed when meaningful, e.g. conversion from int to long goes
* unchecked.
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_integral<Src>::value && !std::is_same<Tgt, Src>::value &&
!std::is_same<Tgt, bool>::value &&
std::is_integral<Tgt>::value,
Expected<Tgt, ConversionCode>>::type
convertTo(const Src& value) noexcept {
/* static */ if (
folly::_t<std::make_unsigned<Tgt>>(std::numeric_limits<Tgt>::max()) <
folly::_t<std::make_unsigned<Src>>(std::numeric_limits<Src>::max())) {
if (greater_than<Tgt, std::numeric_limits<Tgt>::max()>(value)) {
return makeUnexpected(ConversionCode::ARITH_POSITIVE_OVERFLOW);
}
}
/* static */ if (
std::is_signed<Src>::value &&
(!std::is_signed<Tgt>::value || sizeof(Src) > sizeof(Tgt))) {
if (less_than<Tgt, std::numeric_limits<Tgt>::min()>(value)) {
return makeUnexpected(ConversionCode::ARITH_NEGATIVE_OVERFLOW);
}
}
return static_cast<Tgt>(value);
}
/**
* Checked conversion from floating to floating. The checks are only
* performed when meaningful, e.g. conversion from float to double goes
* unchecked.
*/
template <class Tgt, class Src>
typename std::enable_if<
std::is_floating_point<Tgt>::value && std::is_floating_point<Src>::value &&
!std::is_same<Tgt, Src>::value,
Expected<Tgt, ConversionCode>>::type
convertTo(const Src& value) noexcept {
/* static */ if (
std::numeric_limits<Tgt>::max() < std::numeric_limits<Src>::max()) {
if (value > std::numeric_limits<Tgt>::max()) {
return makeUnexpected(ConversionCode::ARITH_POSITIVE_OVERFLOW);
}
if (value < std::numeric_limits<Tgt>::lowest()) {
return makeUnexpected(ConversionCode::ARITH_NEGATIVE_OVERFLOW);
}
}
return static_cast<Tgt>(value);
}
/**
* Check if a floating point value can safely be converted to an
* integer value without triggering undefined behaviour.
*/
template <typename Tgt, typename Src>
inline typename std::enable_if<
std::is_floating_point<Src>::value && std::is_integral<Tgt>::value &&
!std::is_same<Tgt, bool>::value,
bool>::type
checkConversion(const Src& value) {
constexpr Src tgtMaxAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::max());
constexpr Src tgtMinAsSrc = static_cast<Src>(std::numeric_limits<Tgt>::min());
if (value >= tgtMaxAsSrc) {
if (value > tgtMaxAsSrc) {
return false;
}
const Src mmax = folly::nextafter(tgtMaxAsSrc, Src());
if (static_cast<Tgt>(value - mmax) >
std::numeric_limits<Tgt>::max() - static_cast<Tgt>(mmax)) {
return false;
}
} else if (std::is_signed<Tgt>::value && value <= tgtMinAsSrc) {
if (value < tgtMinAsSrc) {
return false;
}
const Src mmin = folly::nextafter(tgtMinAsSrc, Src());
if (static_cast<Tgt>(value - mmin) <
std::numeric_limits<Tgt>::min() - static_cast<Tgt>(mmin)) {
return false;
}
}
return true;
}
// Integers can always safely be converted to floating point values
template <typename Tgt, typename Src>
constexpr typename std::enable_if<
std::is_integral<Src>::value && std::is_floating_point<Tgt>::value,
bool>::type
checkConversion(const Src&) {
return true;
}
// Also, floating point values can always be safely converted to bool
// Per the standard, any floating point value that is not zero will yield true
template <typename Tgt, typename Src>
constexpr typename std::enable_if<
std::is_floating_point<Src>::value && std::is_same<Tgt, bool>::value,
bool>::type
checkConversion(const Src&) {
return true;
}
/**
* Checked conversion from integral to floating point and back. The
* result must be convertible back to the source type without loss of
* precision. This seems Draconian but sometimes is what's needed, and
* complements existing routines nicely. For various rounding
* routines, see <math>.
*/
template <typename Tgt, typename Src>
typename std::enable_if<
(std::is_integral<Src>::value && std::is_floating_point<Tgt>::value) ||
(std::is_floating_point<Src>::value && std::is_integral<Tgt>::value),
Expected<Tgt, ConversionCode>>::type
convertTo(const Src& value) noexcept {
if (LIKELY(checkConversion<Tgt>(value))) {
Tgt result = static_cast<Tgt>(value);
if (LIKELY(checkConversion<Src>(result))) {
Src witness = static_cast<Src>(result);
if (LIKELY(value == witness)) {
return result;
}
}
}
return makeUnexpected(ConversionCode::ARITH_LOSS_OF_PRECISION);
}
template <typename Tgt, typename Src>
inline std::string errorValue(const Src& value) {
#ifdef FOLLY_HAS_RTTI
return to<std::string>("(", demangle(typeid(Tgt)), ") ", value);
#else
return to<std::string>(value);
#endif
}
template <typename Tgt, typename Src>
using IsArithToArith = std::integral_constant<
bool,
!std::is_same<Tgt, Src>::value && !std::is_same<Tgt, bool>::value &&
std::is_arithmetic<Src>::value &&
std::is_arithmetic<Tgt>::value>;
} // namespace detail
template <typename Tgt, typename Src>
typename std::enable_if<
detail::IsArithToArith<Tgt, Src>::value,
Expected<Tgt, ConversionCode>>::type
tryTo(const Src& value) noexcept {
return detail::convertTo<Tgt>(value);
}
template <typename Tgt, typename Src>
typename std::enable_if<detail::IsArithToArith<Tgt, Src>::value, Tgt>::type to(
const Src& value) {
return tryTo<Tgt>(value).thenOrThrow(
[](Tgt res) { return res; },
[&](ConversionCode e) {
return makeConversionError(e, detail::errorValue<Tgt>(value));
});
}
/*******************************************************************************
* Custom Conversions
*
* Any type can be used with folly::to by implementing parseTo. The
* implementation should be provided in the namespace of the type to facilitate
* argument-dependent lookup:
*
* namespace other_namespace {
* ::folly::Expected<::folly::StringPiece, SomeErrorCode>
* parseTo(::folly::StringPiece, OtherType&) noexcept;
* }
******************************************************************************/
template <class T>
FOLLY_WARN_UNUSED_RESULT typename std::enable_if<
std::is_enum<T>::value,
Expected<StringPiece, ConversionCode>>::type
parseTo(StringPiece in, T& out) noexcept {
typename std::underlying_type<T>::type tmp{};
auto restOrError = parseTo(in, tmp);
out = static_cast<T>(tmp); // Harmless if parseTo fails
return restOrError;
}
FOLLY_WARN_UNUSED_RESULT
inline Expected<StringPiece, ConversionCode> parseTo(
StringPiece in,
StringPiece& out) noexcept {
out = in;
return StringPiece{in.end(), in.end()};
}
FOLLY_WARN_UNUSED_RESULT
inline Expected<StringPiece, ConversionCode> parseTo(
StringPiece in,
std::string& out) {
out.clear();
out.append(in.data(), in.size()); // TODO try/catch?
return StringPiece{in.end(), in.end()};
}
FOLLY_WARN_UNUSED_RESULT
inline Expected<StringPiece, ConversionCode> parseTo(
StringPiece in,
fbstring& out) {
out.clear();
out.append(in.data(), in.size()); // TODO try/catch?
return StringPiece{in.end(), in.end()};
}
namespace detail {
template <typename Tgt>
using ParseToResult = decltype(parseTo(StringPiece{}, std::declval<Tgt&>()));
struct CheckTrailingSpace {
Expected<Unit, ConversionCode> operator()(StringPiece sp) const {
auto e = enforceWhitespaceErr(sp);
if (UNLIKELY(e != ConversionCode::SUCCESS))
return makeUnexpected(e);
return unit;
}
};
template <class Error>
struct ReturnUnit {
template <class T>
constexpr Expected<Unit, Error> operator()(T&&) const {
return unit;
}
};
// Older versions of the parseTo customization point threw on error and
// returned void. Handle that.
template <class Tgt>
inline typename std::enable_if<
std::is_void<ParseToResult<Tgt>>::value,
Expected<StringPiece, ConversionCode>>::type
parseToWrap(StringPiece sp, Tgt& out) {
parseTo(sp, out);
return StringPiece(sp.end(), sp.end());
}
template <class Tgt>
inline typename std::enable_if<
!std::is_void<ParseToResult<Tgt>>::value,
ParseToResult<Tgt>>::type
parseToWrap(StringPiece sp, Tgt& out) {
return parseTo(sp, out);
}
template <typename Tgt>
using ParseToError = ExpectedErrorType<decltype(
detail::parseToWrap(StringPiece{}, std::declval<Tgt&>()))>;
} // namespace detail
/**
* String or StringPiece to target conversion. Accepts leading and trailing
* whitespace, but no non-space trailing characters.
*/
template <class Tgt>
inline typename std::enable_if<
!std::is_same<StringPiece, Tgt>::value,
Expected<Tgt, detail::ParseToError<Tgt>>>::type
tryTo(StringPiece src) {
Tgt result{};
using Error = detail::ParseToError<Tgt>;
using Check = typename std::conditional<
std::is_arithmetic<Tgt>::value,
detail::CheckTrailingSpace,
detail::ReturnUnit<Error>>::type;
return parseTo(src, result).then(Check(), [&](Unit) {
return std::move(result);
});
}
template <class Tgt>
inline
typename std::enable_if<!std::is_same<StringPiece, Tgt>::value, Tgt>::type
to(StringPiece src) {
Tgt result{};
using Error = detail::ParseToError<Tgt>;
using Check = typename std::conditional<
std::is_arithmetic<Tgt>::value,
detail::CheckTrailingSpace,
detail::ReturnUnit<Error>>::type;
auto tmp = detail::parseToWrap(src, result);
return tmp
.thenOrThrow(Check(), [&](Error e) { throw makeConversionError(e, src); })
.thenOrThrow(
[&](Unit) { return std::move(result); },
[&](Error e) { throw makeConversionError(e, tmp.value()); });
}
/**
* tryTo/to that take the strings by pointer so the caller gets information
* about how much of the string was consumed by the conversion. These do not
* check for trailing whitepsace.
*/
template <class Tgt>
Expected<Tgt, detail::ParseToError<Tgt>> tryTo(StringPiece* src) {
Tgt result;
return parseTo(*src, result).then([&, src](StringPiece sp) -> Tgt {
*src = sp;
return std::move(result);
});
}
template <class Tgt>
Tgt to(StringPiece* src) {
Tgt result{};
using Error = detail::ParseToError<Tgt>;
return parseTo(*src, result)
.thenOrThrow(
[&, src](StringPiece sp) -> Tgt {
*src = sp;
return std::move(result);
},
[=](Error e) { return makeConversionError(e, *src); });
}
/*******************************************************************************
* Enum to anything and back
******************************************************************************/
template <class Tgt, class Src>
typename std::enable_if<
std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value,
Expected<Tgt, ConversionCode>>::type
tryTo(const Src& value) {
using I = typename std::underlying_type<Src>::type;
return tryTo<Tgt>(static_cast<I>(value));
}
template <class Tgt, class Src>
typename std::enable_if<
std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value,
Tgt>::type
tryTo(const Src& value) {
using I = typename std::underlying_type<Tgt>::type;
return tryTo<I>(value).then([](I i) { return static_cast<Tgt>(i); });
}
template <class Tgt, class Src>
typename std::enable_if<
std::is_enum<Src>::value && !std::is_same<Src, Tgt>::value,
Tgt>::type
to(const Src& value) {
return to<Tgt>(static_cast<typename std::underlying_type<Src>::type>(value));
}
template <class Tgt, class Src>
typename std::enable_if<
std::is_enum<Tgt>::value && !std::is_same<Src, Tgt>::value, Tgt>::type
to(const Src & value) {
return static_cast<Tgt>(to<typename std::underlying_type<Tgt>::type>(value));
}
} // namespace folly