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// Copyright 2017 The Abseil Authors.
// 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
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// See the License for the specific language governing permissions and
// limitations under the License.
// This file declares INTERNAL parts of the Split API that are inline/templated
// or otherwise need to be available at compile time. The main abstractions
// defined in here are
// - ConvertibleToStringView
// - SplitIterator<>
// - Splitter<>
// DO NOT INCLUDE THIS FILE DIRECTLY. Use this file by including
// absl/strings/str_split.h.
// IWYU pragma: private, include "absl/strings/str_split.h"
#include <array>
#include <initializer_list>
#include <iterator>
#include <map>
#include <type_traits>
#include <utility>
#include <vector>
#include "absl/base/macros.h"
#include "absl/base/port.h"
#include "absl/meta/type_traits.h"
#include "absl/strings/string_view.h"
#include "absl/strings/internal/stl_type_traits.h"
#endif // _GLIBCXX_DEBUG
namespace absl {
namespace strings_internal {
// This class is implicitly constructible from everything that absl::string_view
// is implicitly constructible from. If it's constructed from a temporary
// string, the data is moved into a data member so its lifetime matches that of
// the ConvertibleToStringView instance.
class ConvertibleToStringView {
ConvertibleToStringView(const char* s) // NOLINT(runtime/explicit)
: value_(s) {}
ConvertibleToStringView(char* s) : value_(s) {} // NOLINT(runtime/explicit)
ConvertibleToStringView(absl::string_view s) // NOLINT(runtime/explicit)
: value_(s) {}
ConvertibleToStringView(const std::string& s) // NOLINT(runtime/explicit)
: value_(s) {}
// Matches rvalue strings and moves their data to a member.
ConvertibleToStringView(std::string&& s) // NOLINT(runtime/explicit)
: copy_(std::move(s)), value_(copy_), self_referential_(true) {}
ConvertibleToStringView(const ConvertibleToStringView& other)
: value_(other.value_), self_referential_(other.self_referential_) {
if (other.self_referential_) {
new (&copy_) std::string(other.copy_);
value_ = copy_;
ConvertibleToStringView(ConvertibleToStringView&& other)
: value_(other.value_), self_referential_(other.self_referential_) {
if (other.self_referential_) {
new (&copy_) std::string(std::move(other.copy_));
value_ = copy_;
ConvertibleToStringView& operator=(ConvertibleToStringView other) {
new (this) ConvertibleToStringView(std::move(other));
return *this;
absl::string_view value() const { return value_; }
~ConvertibleToStringView() { MaybeReleaseCopy(); }
void MaybeReleaseCopy() {
if (self_referential_) {
// An explicit destructor call cannot be a qualified name such as
// std::string. The "using" declaration works around this
// issue by creating an unqualified name for the destructor.
using string_type = std::string;
struct Unused { // MSVC disallows unions with only 1 member.
// Holds the data moved from temporary std::string arguments. Declared first
// so that 'value' can refer to 'copy_'.
union {
std::string copy_;
Unused unused_;
absl::string_view value_;
// true if value_ refers to the internal copy_ member.
bool self_referential_ = false;
// An iterator that enumerates the parts of a string from a Splitter. The text
// to be split, the Delimiter, and the Predicate are all taken from the given
// Splitter object. Iterators may only be compared if they refer to the same
// Splitter instance.
// This class is NOT part of the public splitting API.
template <typename Splitter>
class SplitIterator {
using iterator_category = std::input_iterator_tag;
using value_type = absl::string_view;
using difference_type = ptrdiff_t;
using pointer = const value_type*;
using reference = const value_type&;
enum State { kInitState, kLastState, kEndState };
SplitIterator(State state, const Splitter* splitter)
: pos_(0),
predicate_(splitter->predicate()) {
// Hack to maintain backward compatibility. This one block makes it so an
// empty absl::string_view whose .data() happens to be nullptr behaves
// *differently* from an otherwise empty absl::string_view whose .data() is
// not nullptr. This is an undesirable difference in general, but this
// behavior is maintained to avoid breaking existing code that happens to
// depend on this old behavior/bug. Perhaps it will be fixed one day. The
// difference in behavior is as follows:
// Split(absl::string_view(""), '-'); // {""}
// Split(absl::string_view(), '-'); // {}
if (splitter_->text().data() == nullptr) {
state_ = kEndState;
pos_ = splitter_->text().size();
if (state_ == kEndState) {
pos_ = splitter_->text().size();
} else {
bool at_end() const { return state_ == kEndState; }
reference operator*() const { return curr_; }
pointer operator->() const { return &curr_; }
SplitIterator& operator++() {
do {
if (state_ == kLastState) {
state_ = kEndState;
return *this;
const absl::string_view text = splitter_->text();
const absl::string_view d = delimiter_.Find(text, pos_);
if ( == + text.size()) state_ = kLastState;
curr_ = text.substr(pos_, - ( + pos_));
pos_ += curr_.size() + d.size();
} while (!predicate_(curr_));
return *this;
SplitIterator operator++(int) {
SplitIterator old(*this);
return old;
friend bool operator==(const SplitIterator& a, const SplitIterator& b) {
return a.state_ == b.state_ && a.pos_ == b.pos_;
friend bool operator!=(const SplitIterator& a, const SplitIterator& b) {
return !(a == b);
size_t pos_;
State state_;
absl::string_view curr_;
const Splitter* splitter_;
typename Splitter::DelimiterType delimiter_;
typename Splitter::PredicateType predicate_;
// HasMappedType<T>::value is true iff there exists a type T::mapped_type.
template <typename T, typename = void>
struct HasMappedType : std::false_type {};
template <typename T>
struct HasMappedType<T, absl::void_t<typename T::mapped_type>>
: std::true_type {};
// HasValueType<T>::value is true iff there exists a type T::value_type.
template <typename T, typename = void>
struct HasValueType : std::false_type {};
template <typename T>
struct HasValueType<T, absl::void_t<typename T::value_type>> : std::true_type {
// HasConstIterator<T>::value is true iff there exists a type T::const_iterator.
template <typename T, typename = void>
struct HasConstIterator : std::false_type {};
template <typename T>
struct HasConstIterator<T, absl::void_t<typename T::const_iterator>>
: std::true_type {};
// IsInitializerList<T>::value is true iff T is an std::initializer_list. More
// details below in Splitter<> where this is used.
std::false_type IsInitializerListDispatch(...); // default: No
template <typename T>
std::true_type IsInitializerListDispatch(std::initializer_list<T>*);
template <typename T>
struct IsInitializerList
: decltype(IsInitializerListDispatch(static_cast<T*>(nullptr))) {};
// A SplitterIsConvertibleTo<C>::type alias exists iff the specified condition
// is true for type 'C'.
// Restricts conversion to container-like types (by testing for the presence of
// a const_iterator member type) and also to disable conversion to an
// std::initializer_list (which also has a const_iterator). Otherwise, code
// compiled in C++11 will get an error due to ambiguous conversion paths (in
// C++11 std::vector<T>::operator= is overloaded to take either a std::vector<T>
// or an std::initializer_list<T>).
template <typename C, bool has_value_type, bool has_mapped_type>
struct SplitterIsConvertibleToImpl : std::false_type {};
template <typename C>
struct SplitterIsConvertibleToImpl<C, true, false>
: std::is_constructible<typename C::value_type, absl::string_view> {};
template <typename C>
struct SplitterIsConvertibleToImpl<C, true, true>
: absl::conjunction<
std::is_constructible<typename C::key_type, absl::string_view>,
std::is_constructible<typename C::mapped_type, absl::string_view>> {};
template <typename C>
struct SplitterIsConvertibleTo
: SplitterIsConvertibleToImpl<
!IsStrictlyBaseOfAndConvertibleToSTLContainer<C>::value &&
#endif // _GLIBCXX_DEBUG
typename std::remove_reference<C>::type>::value &&
HasValueType<C>::value && HasConstIterator<C>::value,
HasMappedType<C>::value> {
// This class implements the range that is returned by absl::StrSplit(). This
// class has templated conversion operators that allow it to be implicitly
// converted to a variety of types that the caller may have specified on the
// left-hand side of an assignment.
// The main interface for interacting with this class is through its implicit
// conversion operators. However, this class may also be used like a container
// in that it has .begin() and .end() member functions. It may also be used
// within a range-for loop.
// Output containers can be collections of any type that is constructible from
// an absl::string_view.
// An Predicate functor may be supplied. This predicate will be used to filter
// the split strings: only strings for which the predicate returns true will be
// kept. A Predicate object is any unary functor that takes an absl::string_view
// and returns bool.
template <typename Delimiter, typename Predicate>
class Splitter {
using DelimiterType = Delimiter;
using PredicateType = Predicate;
using const_iterator = strings_internal::SplitIterator<Splitter>;
using value_type = typename std::iterator_traits<const_iterator>::value_type;
Splitter(ConvertibleToStringView input_text, Delimiter d, Predicate p)
: text_(std::move(input_text)),
predicate_(std::move(p)) {}
absl::string_view text() const { return text_.value(); }
const Delimiter& delimiter() const { return delimiter_; }
const Predicate& predicate() const { return predicate_; }
// Range functions that iterate the split substrings as absl::string_view
// objects. These methods enable a Splitter to be used in a range-based for
// loop.
const_iterator begin() const { return {const_iterator::kInitState, this}; }
const_iterator end() const { return {const_iterator::kEndState, this}; }
// An implicit conversion operator that is restricted to only those containers
// that the splitter is convertible to.
template <typename Container,
typename = typename std::enable_if<
operator Container() const { // NOLINT(runtime/explicit)
return ConvertToContainer<Container, typename Container::value_type,
// Returns a pair with its .first and .second members set to the first two
// strings returned by the begin() iterator. Either/both of .first and .second
// will be constructed with empty strings if the iterator doesn't have a
// corresponding value.
template <typename First, typename Second>
operator std::pair<First, Second>() const { // NOLINT(runtime/explicit)
absl::string_view first, second;
auto it = begin();
if (it != end()) {
first = *it;
if (++it != end()) {
second = *it;
return {First(first), Second(second)};
// ConvertToContainer is a functor converting a Splitter to the requested
// Container of ValueType. It is specialized below to optimize splitting to
// certain combinations of Container and ValueType.
// This base template handles the generic case of storing the split results in
// the requested non-map-like container and converting the split substrings to
// the requested type.
template <typename Container, typename ValueType, bool is_map = false>
struct ConvertToContainer {
Container operator()(const Splitter& splitter) const {
Container c;
auto it = std::inserter(c, c.end());
for (const auto& sp : splitter) {
*it++ = ValueType(sp);
return c;
// Partial specialization for a std::vector<absl::string_view>.
// Optimized for the common case of splitting to a
// std::vector<absl::string_view>. In this case we first split the results to
// a small array of absl::string_view on the stack, to reduce reallocations.
template <typename A>
struct ConvertToContainer<std::vector<absl::string_view, A>,
absl::string_view, false> {
std::vector<absl::string_view, A> operator()(
const Splitter& splitter) const {
struct raw_view {
const char* data;
size_t size;
operator absl::string_view() const { // NOLINT(runtime/explicit)
return {data, size};
std::vector<absl::string_view, A> v;
std::array<raw_view, 16> ar;
for (auto it = splitter.begin(); !it.at_end();) {
size_t index = 0;
do {
ar[index].data = it->data();
ar[index].size = it->size();
} while (++index != ar.size() && !it.at_end());
v.insert(v.end(), ar.begin(), ar.begin() + index);
return v;
// Partial specialization for a std::vector<std::string>.
// Optimized for the common case of splitting to a std::vector<std::string>.
// In this case we first split the results to a std::vector<absl::string_view>
// so the returned std::vector<std::string> can have space reserved to avoid
// std::string moves.
template <typename A>
struct ConvertToContainer<std::vector<std::string, A>, std::string, false> {
std::vector<std::string, A> operator()(const Splitter& splitter) const {
const std::vector<absl::string_view> v = splitter;
return std::vector<std::string, A>(v.begin(), v.end());
// Partial specialization for containers of pairs (e.g., maps).
// The algorithm is to insert a new pair into the map for each even-numbered
// item, with the even-numbered item as the key with a default-constructed
// value. Each odd-numbered item will then be assigned to the last pair's
// value.
template <typename Container, typename First, typename Second>
struct ConvertToContainer<Container, std::pair<const First, Second>, true> {
Container operator()(const Splitter& splitter) const {
Container m;
typename Container::iterator it;
bool insert = true;
for (const auto& sp : splitter) {
if (insert) {
it = Inserter<Container>::Insert(&m, First(sp), Second());
} else {
it->second = Second(sp);
insert = !insert;
return m;
// Inserts the key and value into the given map, returning an iterator to
// the inserted item. Specialized for std::map and std::multimap to use
// emplace() and adapt emplace()'s return value.
template <typename Map>
struct Inserter {
using M = Map;
template <typename... Args>
static typename M::iterator Insert(M* m, Args&&... args) {
return m->insert(std::make_pair(std::forward<Args>(args)...)).first;
template <typename... Ts>
struct Inserter<std::map<Ts...>> {
using M = std::map<Ts...>;
template <typename... Args>
static typename M::iterator Insert(M* m, Args&&... args) {
return m->emplace(std::make_pair(std::forward<Args>(args)...)).first;
template <typename... Ts>
struct Inserter<std::multimap<Ts...>> {
using M = std::multimap<Ts...>;
template <typename... Args>
static typename M::iterator Insert(M* m, Args&&... args) {
return m->emplace(std::make_pair(std::forward<Args>(args)...));
ConvertibleToStringView text_;
Delimiter delimiter_;
Predicate predicate_;
} // namespace strings_internal
} // namespace absl