about summary refs log tree commit diff
path: root/absl/strings/internal/str_split_internal.h
blob: 81e8d55544680d671e56eb0254995b42bd548d40 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
// 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
//
//      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.
//

// 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"

#ifndef ABSL_STRINGS_INTERNAL_STR_SPLIT_INTERNAL_H_
#define ABSL_STRINGS_INTERNAL_STR_SPLIT_INTERNAL_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"

#ifdef _GLIBCXX_DEBUG
#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 {
 public:
  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_) {}

  ConvertibleToStringView(const ConvertibleToStringView& other)
      : copy_(other.copy_),
        value_(other.IsSelfReferential() ? copy_ : other.value_) {}

  ConvertibleToStringView(ConvertibleToStringView&& other) {
    StealMembers(std::move(other));
  }

  ConvertibleToStringView& operator=(ConvertibleToStringView other) {
    StealMembers(std::move(other));
    return *this;
  }

  absl::string_view value() const { return value_; }

 private:
  // Returns true if ctsp's value refers to its internal copy_ member.
  bool IsSelfReferential() const { return value_.data() == copy_.data(); }

  void StealMembers(ConvertibleToStringView&& other) {
    if (other.IsSelfReferential()) {
      copy_ = std::move(other.copy_);
      value_ = copy_;
      other.value_ = other.copy_;
    } else {
      value_ = other.value_;
    }
  }

  // Holds the data moved from temporary std::string arguments. Declared first so
  // that 'value' can refer to 'copy_'.
  std::string copy_;
  absl::string_view value_;
};

// 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 {
 public:
  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),
        state_(state),
        splitter_(splitter),
        delimiter_(splitter->delimiter()),
        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();
      return;
    }

    if (state_ == kEndState) {
      pos_ = splitter_->text().size();
    } else {
      ++(*this);
    }
  }

  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 (d.data() == text.data() + text.size()) state_ = kLastState;
      curr_ = text.substr(pos_, d.data() - (text.data() + pos_));
      pos_ += curr_.size() + d.size();
    } while (!predicate_(curr_));
    return *this;
  }

  SplitIterator operator++(int) {
    SplitIterator old(*this);
    ++(*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);
  }

 private:
  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<
          C,
#ifdef _GLIBCXX_DEBUG
          !IsStrictlyBaseOfAndConvertibleToSTLContainer<C>::value &&
#endif  // _GLIBCXX_DEBUG
              !IsInitializerList<
                  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 {
 public:
  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)),
        delimiter_(std::move(d)),
        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<
                SplitterIsConvertibleTo<Container>::value>::type>
  operator Container() const {  // NOLINT(runtime/explicit)
    return ConvertToContainer<Container, typename Container::value_type,
                              HasMappedType<Container>::value>()(*this);
  }

  // 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)};
  }

 private:
  // 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();
          ++it;
        } 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

#endif  // ABSL_STRINGS_INTERNAL_STR_SPLIT_INTERNAL_H_