about summary refs log tree commit diff
path: root/absl/strings/internal/str_join_internal.h
blob: 31dbf672f0b602e51e2101660338094dd71dabfb (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
//
// 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
//
//      https://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 Join API that are inlined/templated
// or otherwise need to be available at compile time. The main abstractions
// defined in this file are:
//
//   - A handful of default Formatters
//   - JoinAlgorithm() overloads
//   - JoinRange() overloads
//   - JoinTuple()
//
// DO NOT INCLUDE THIS FILE DIRECTLY. Use this file by including
// absl/strings/str_join.h
//
// IWYU pragma: private, include "absl/strings/str_join.h"

#ifndef ABSL_STRINGS_INTERNAL_STR_JOIN_INTERNAL_H_
#define ABSL_STRINGS_INTERNAL_STR_JOIN_INTERNAL_H_

#include <cstring>
#include <iterator>
#include <memory>
#include <string>
#include <type_traits>
#include <utility>

#include "absl/strings/internal/ostringstream.h"
#include "absl/strings/internal/resize_uninitialized.h"
#include "absl/strings/str_cat.h"

namespace absl {
ABSL_NAMESPACE_BEGIN
namespace strings_internal {

//
// Formatter objects
//
// The following are implementation classes for standard Formatter objects. The
// factory functions that users will call to create and use these formatters are
// defined and documented in strings/join.h.
//

// The default formatter. Converts alpha-numeric types to strings.
struct AlphaNumFormatterImpl {
  // This template is needed in order to support passing in a dereferenced
  // vector<bool>::iterator
  template <typename T>
  void operator()(std::string* out, const T& t) const {
    StrAppend(out, AlphaNum(t));
  }

  void operator()(std::string* out, const AlphaNum& t) const {
    StrAppend(out, t);
  }
};

// A type that's used to overload the JoinAlgorithm() function (defined below)
// for ranges that do not require additional formatting (e.g., a range of
// strings).

struct NoFormatter : public AlphaNumFormatterImpl {};

// Formats types to strings using the << operator.
class StreamFormatterImpl {
 public:
  // The method isn't const because it mutates state. Making it const will
  // render StreamFormatterImpl thread-hostile.
  template <typename T>
  void operator()(std::string* out, const T& t) {
    // The stream is created lazily to avoid paying the relatively high cost
    // of its construction when joining an empty range.
    if (strm_) {
      strm_->clear();  // clear the bad, fail and eof bits in case they were set
      strm_->str(out);
    } else {
      strm_.reset(new strings_internal::OStringStream(out));
    }
    *strm_ << t;
  }

 private:
  std::unique_ptr<strings_internal::OStringStream> strm_;
};

// Formats a std::pair<>. The 'first' member is formatted using f1_ and the
// 'second' member is formatted using f2_. sep_ is the separator.
template <typename F1, typename F2>
class PairFormatterImpl {
 public:
  PairFormatterImpl(F1 f1, absl::string_view sep, F2 f2)
      : f1_(std::move(f1)), sep_(sep), f2_(std::move(f2)) {}

  template <typename T>
  void operator()(std::string* out, const T& p) {
    f1_(out, p.first);
    out->append(sep_);
    f2_(out, p.second);
  }

  template <typename T>
  void operator()(std::string* out, const T& p) const {
    f1_(out, p.first);
    out->append(sep_);
    f2_(out, p.second);
  }

 private:
  F1 f1_;
  std::string sep_;
  F2 f2_;
};

// Wraps another formatter and dereferences the argument to operator() then
// passes the dereferenced argument to the wrapped formatter. This can be
// useful, for example, to join a std::vector<int*>.
template <typename Formatter>
class DereferenceFormatterImpl {
 public:
  DereferenceFormatterImpl() : f_() {}
  explicit DereferenceFormatterImpl(Formatter&& f)
      : f_(std::forward<Formatter>(f)) {}

  template <typename T>
  void operator()(std::string* out, const T& t) {
    f_(out, *t);
  }

  template <typename T>
  void operator()(std::string* out, const T& t) const {
    f_(out, *t);
  }

 private:
  Formatter f_;
};

// DefaultFormatter<T> is a traits class that selects a default Formatter to use
// for the given type T. The ::Type member names the Formatter to use. This is
// used by the strings::Join() functions that do NOT take a Formatter argument,
// in which case a default Formatter must be chosen.
//
// AlphaNumFormatterImpl is the default in the base template, followed by
// specializations for other types.
template <typename ValueType>
struct DefaultFormatter {
  typedef AlphaNumFormatterImpl Type;
};
template <>
struct DefaultFormatter<const char*> {
  typedef AlphaNumFormatterImpl Type;
};
template <>
struct DefaultFormatter<char*> {
  typedef AlphaNumFormatterImpl Type;
};
template <>
struct DefaultFormatter<std::string> {
  typedef NoFormatter Type;
};
template <>
struct DefaultFormatter<absl::string_view> {
  typedef NoFormatter Type;
};
template <typename ValueType>
struct DefaultFormatter<ValueType*> {
  typedef DereferenceFormatterImpl<typename DefaultFormatter<ValueType>::Type>
      Type;
};

template <typename ValueType>
struct DefaultFormatter<std::unique_ptr<ValueType>>
    : public DefaultFormatter<ValueType*> {};

//
// JoinAlgorithm() functions
//

// The main joining algorithm. This simply joins the elements in the given
// iterator range, each separated by the given separator, into an output string,
// and formats each element using the provided Formatter object.
template <typename Iterator, typename Formatter>
std::string JoinAlgorithm(Iterator start, Iterator end, absl::string_view s,
                          Formatter&& f) {
  std::string result;
  absl::string_view sep("");
  for (Iterator it = start; it != end; ++it) {
    result.append(sep.data(), sep.size());
    f(&result, *it);
    sep = s;
  }
  return result;
}

// A joining algorithm that's optimized for a forward iterator range of
// string-like objects that do not need any additional formatting. This is to
// optimize the common case of joining, say, a std::vector<string> or a
// std::vector<absl::string_view>.
//
// This is an overload of the previous JoinAlgorithm() function. Here the
// Formatter argument is of type NoFormatter. Since NoFormatter is an internal
// type, this overload is only invoked when strings::Join() is called with a
// range of string-like objects (e.g., std::string, absl::string_view), and an
// explicit Formatter argument was NOT specified.
//
// The optimization is that the needed space will be reserved in the output
// string to avoid the need to resize while appending. To do this, the iterator
// range will be traversed twice: once to calculate the total needed size, and
// then again to copy the elements and delimiters to the output string.
template <typename Iterator,
          typename = typename std::enable_if<std::is_convertible<
              typename std::iterator_traits<Iterator>::iterator_category,
              std::forward_iterator_tag>::value>::type>
std::string JoinAlgorithm(Iterator start, Iterator end, absl::string_view s,
                          NoFormatter) {
  std::string result;
  if (start != end) {
    // Sums size
    size_t result_size = start->size();
    for (Iterator it = start; ++it != end;) {
      result_size += s.size();
      result_size += it->size();
    }

    if (result_size > 0) {
      STLStringResizeUninitialized(&result, result_size);

      // Joins strings
      char* result_buf = &*result.begin();
      memcpy(result_buf, start->data(), start->size());
      result_buf += start->size();
      for (Iterator it = start; ++it != end;) {
        memcpy(result_buf, s.data(), s.size());
        result_buf += s.size();
        memcpy(result_buf, it->data(), it->size());
        result_buf += it->size();
      }
    }
  }

  return result;
}

// JoinTupleLoop implements a loop over the elements of a std::tuple, which
// are heterogeneous. The primary template matches the tuple interior case. It
// continues the iteration after appending a separator (for nonzero indices)
// and formatting an element of the tuple. The specialization for the I=N case
// matches the end-of-tuple, and terminates the iteration.
template <size_t I, size_t N>
struct JoinTupleLoop {
  template <typename Tup, typename Formatter>
  void operator()(std::string* out, const Tup& tup, absl::string_view sep,
                  Formatter&& fmt) {
    if (I > 0) out->append(sep.data(), sep.size());
    fmt(out, std::get<I>(tup));
    JoinTupleLoop<I + 1, N>()(out, tup, sep, fmt);
  }
};
template <size_t N>
struct JoinTupleLoop<N, N> {
  template <typename Tup, typename Formatter>
  void operator()(std::string*, const Tup&, absl::string_view, Formatter&&) {}
};

template <typename... T, typename Formatter>
std::string JoinAlgorithm(const std::tuple<T...>& tup, absl::string_view sep,
                          Formatter&& fmt) {
  std::string result;
  JoinTupleLoop<0, sizeof...(T)>()(&result, tup, sep, fmt);
  return result;
}

template <typename Iterator>
std::string JoinRange(Iterator first, Iterator last,
                      absl::string_view separator) {
  // No formatter was explicitly given, so a default must be chosen.
  typedef typename std::iterator_traits<Iterator>::value_type ValueType;
  typedef typename DefaultFormatter<ValueType>::Type Formatter;
  return JoinAlgorithm(first, last, separator, Formatter());
}

template <typename Range, typename Formatter>
std::string JoinRange(const Range& range, absl::string_view separator,
                      Formatter&& fmt) {
  using std::begin;
  using std::end;
  return JoinAlgorithm(begin(range), end(range), separator, fmt);
}

template <typename Range>
std::string JoinRange(const Range& range, absl::string_view separator) {
  using std::begin;
  using std::end;
  return JoinRange(begin(range), end(range), separator);
}

}  // namespace strings_internal
ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_STRINGS_INTERNAL_STR_JOIN_INTERNAL_H_