summaryrefslogtreecommitdiff
path: root/absl/strings/str_format.h
blob: 023e4350d378bcbfeb43a6ed151f87e82e46353d (plain)
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
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
//
// Copyright 2018 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.
//
// -----------------------------------------------------------------------------
// File: str_format.h
// -----------------------------------------------------------------------------
//
// The `str_format` library is a typesafe replacement for the family of
// `printf()` string formatting routines within the `<cstdio>` standard library
// header. Like the `printf` family, `str_format` uses a "format string" to
// perform argument substitutions based on types. See the `FormatSpec` section
// below for format string documentation.
//
// Example:
//
//   std::string s = absl::StrFormat(
//                      "%s %s You have $%d!", "Hello", name, dollars);
//
// The library consists of the following basic utilities:
//
//   * `absl::StrFormat()`, a type-safe replacement for `std::sprintf()`, to
//     write a format string to a `string` value.
//   * `absl::StrAppendFormat()` to append a format string to a `string`
//   * `absl::StreamFormat()` to more efficiently write a format string to a
//     stream, such as`std::cout`.
//   * `absl::PrintF()`, `absl::FPrintF()` and `absl::SNPrintF()` as
//     drop-in replacements for `std::printf()`, `std::fprintf()` and
//     `std::snprintf()`.
//
//     Note: An `absl::SPrintF()` drop-in replacement is not supported as it
//     is generally unsafe due to buffer overflows. Use `absl::StrFormat` which
//     returns the string as output instead of expecting a pre-allocated buffer.
//
// Additionally, you can provide a format string (and its associated arguments)
// using one of the following abstractions:
//
//   * A `FormatSpec` class template fully encapsulates a format string and its
//     type arguments and is usually provided to `str_format` functions as a
//     variadic argument of type `FormatSpec<Arg...>`. The `FormatSpec<Args...>`
//     template is evaluated at compile-time, providing type safety.
//   * A `ParsedFormat` instance, which encapsulates a specific, pre-compiled
//     format string for a specific set of type(s), and which can be passed
//     between API boundaries. (The `FormatSpec` type should not be used
//     directly except as an argument type for wrapper functions.)
//
// The `str_format` library provides the ability to output its format strings to
// arbitrary sink types:
//
//   * A generic `Format()` function to write outputs to arbitrary sink types,
//     which must implement a `FormatRawSink` interface.
//
//   * A `FormatUntyped()` function that is similar to `Format()` except it is
//     loosely typed. `FormatUntyped()` is not a template and does not perform
//     any compile-time checking of the format string; instead, it returns a
//     boolean from a runtime check.
//
// In addition, the `str_format` library provides extension points for
// augmenting formatting to new types.  See "StrFormat Extensions" below.

#ifndef ABSL_STRINGS_STR_FORMAT_H_
#define ABSL_STRINGS_STR_FORMAT_H_

#include <cstdio>
#include <string>

#include "absl/strings/internal/str_format/arg.h"  // IWYU pragma: export
#include "absl/strings/internal/str_format/bind.h"  // IWYU pragma: export
#include "absl/strings/internal/str_format/checker.h"  // IWYU pragma: export
#include "absl/strings/internal/str_format/extension.h"  // IWYU pragma: export
#include "absl/strings/internal/str_format/parser.h"  // IWYU pragma: export

namespace absl {
ABSL_NAMESPACE_BEGIN

// UntypedFormatSpec
//
// A type-erased class that can be used directly within untyped API entry
// points. An `UntypedFormatSpec` is specifically used as an argument to
// `FormatUntyped()`.
//
// Example:
//
//   absl::UntypedFormatSpec format("%d");
//   std::string out;
//   CHECK(absl::FormatUntyped(&out, format, {absl::FormatArg(1)}));
class UntypedFormatSpec {
 public:
  UntypedFormatSpec() = delete;
  UntypedFormatSpec(const UntypedFormatSpec&) = delete;
  UntypedFormatSpec& operator=(const UntypedFormatSpec&) = delete;

  explicit UntypedFormatSpec(string_view s) : spec_(s) {}

 protected:
  explicit UntypedFormatSpec(const str_format_internal::ParsedFormatBase* pc)
      : spec_(pc) {}

 private:
  friend str_format_internal::UntypedFormatSpecImpl;
  str_format_internal::UntypedFormatSpecImpl spec_;
};

// FormatStreamed()
//
// Takes a streamable argument and returns an object that can print it
// with '%s'. Allows printing of types that have an `operator<<` but no
// intrinsic type support within `StrFormat()` itself.
//
// Example:
//
//   absl::StrFormat("%s", absl::FormatStreamed(obj));
template <typename T>
str_format_internal::StreamedWrapper<T> FormatStreamed(const T& v) {
  return str_format_internal::StreamedWrapper<T>(v);
}

// FormatCountCapture
//
// This class provides a way to safely wrap `StrFormat()` captures of `%n`
// conversions, which denote the number of characters written by a formatting
// operation to this point, into an integer value.
//
// This wrapper is designed to allow safe usage of `%n` within `StrFormat(); in
// the `printf()` family of functions, `%n` is not safe to use, as the `int *`
// buffer can be used to capture arbitrary data.
//
// Example:
//
//   int n = 0;
//   std::string s = absl::StrFormat("%s%d%n", "hello", 123,
//                       absl::FormatCountCapture(&n));
//   EXPECT_EQ(8, n);
class FormatCountCapture {
 public:
  explicit FormatCountCapture(int* p) : p_(p) {}

 private:
  // FormatCountCaptureHelper is used to define FormatConvertImpl() for this
  // class.
  friend struct str_format_internal::FormatCountCaptureHelper;
  // Unused() is here because of the false positive from -Wunused-private-field
  // p_ is used in the templated function of the friend FormatCountCaptureHelper
  // class.
  int* Unused() { return p_; }
  int* p_;
};

// FormatSpec
//
// The `FormatSpec` type defines the makeup of a format string within the
// `str_format` library. It is a variadic class template that is evaluated at
// compile-time, according to the format string and arguments that are passed to
// it.
//
// You should not need to manipulate this type directly. You should only name it
// if you are writing wrapper functions which accept format arguments that will
// be provided unmodified to functions in this library. Such a wrapper function
// might be a class method that provides format arguments and/or internally uses
// the result of formatting.
//
// For a `FormatSpec` to be valid at compile-time, it must be provided as
// either:
//
// * A `constexpr` literal or `absl::string_view`, which is how it most often
//   used.
// * A `ParsedFormat` instantiation, which ensures the format string is
//   valid before use. (See below.)
//
// Example:
//
//   // Provided as a string literal.
//   absl::StrFormat("Welcome to %s, Number %d!", "The Village", 6);
//
//   // Provided as a constexpr absl::string_view.
//   constexpr absl::string_view formatString = "Welcome to %s, Number %d!";
//   absl::StrFormat(formatString, "The Village", 6);
//
//   // Provided as a pre-compiled ParsedFormat object.
//   // Note that this example is useful only for illustration purposes.
//   absl::ParsedFormat<'s', 'd'> formatString("Welcome to %s, Number %d!");
//   absl::StrFormat(formatString, "TheVillage", 6);
//
// A format string generally follows the POSIX syntax as used within the POSIX
// `printf` specification. (Exceptions are noted below.)
//
// (See http://pubs.opengroup.org/onlinepubs/9699919799/functions/fprintf.html)
//
// In specific, the `FormatSpec` supports the following type specifiers:
//   * `c` for characters
//   * `s` for strings
//   * `d` or `i` for integers
//   * `o` for unsigned integer conversions into octal
//   * `x` or `X` for unsigned integer conversions into hex
//   * `u` for unsigned integers
//   * `f` or `F` for floating point values into decimal notation
//   * `e` or `E` for floating point values into exponential notation
//   * `a` or `A` for floating point values into hex exponential notation
//   * `g` or `G` for floating point values into decimal or exponential
//     notation based on their precision
//   * `p` for pointer address values
//   * `n` for the special case of writing out the number of characters
//     written to this point. The resulting value must be captured within an
//     `absl::FormatCountCapture` type.
//   * `v` for values using the default format for a deduced type. These deduced
//     types include many of the primitive types denoted here as well as
//     user-defined types containing the proper extensions. (See below for more
//     information.)
//
// Implementation-defined behavior:
//   * A null pointer provided to "%s" or "%p" is output as "(nil)".
//   * A non-null pointer provided to "%p" is output in hex as if by %#x or
//     %#lx.
//
// NOTE: `o`, `x\X` and `u` will convert signed values to their unsigned
// counterpart before formatting.
//
// Examples:
//     "%c", 'a'                -> "a"
//     "%c", 32                 -> " "
//     "%s", "C"                -> "C"
//     "%s", std::string("C++") -> "C++"
//     "%d", -10                -> "-10"
//     "%o", 10                 -> "12"
//     "%x", 16                 -> "10"
//     "%f", 123456789          -> "123456789.000000"
//     "%e", .01                -> "1.00000e-2"
//     "%a", -3.0               -> "-0x1.8p+1"
//     "%g", .01                -> "1e-2"
//     "%p", (void*)&value      -> "0x7ffdeb6ad2a4"
//
//     int n = 0;
//     std::string s = absl::StrFormat(
//         "%s%d%n", "hello", 123, absl::FormatCountCapture(&n));
//     EXPECT_EQ(8, n);
//
// NOTE: the `v` specifier (for "value") is a type specifier not present in the
// POSIX specification. %v will format values according to their deduced type.
// `v` uses `d` for signed integer values, `u` for unsigned integer values, `g`
// for floating point values, and formats boolean values as "true"/"false"
// (instead of 1 or 0 for booleans formatted using d). `const char*` is not
// supported; please use `std:string` and `string_view`. `char` is also not
// supported due to ambiguity of the type. This specifier does not support
// modifiers.
//
// The `FormatSpec` intrinsically supports all of these fundamental C++ types:
//
// *   Characters: `char`, `signed char`, `unsigned char`
// *   Integers: `int`, `short`, `unsigned short`, `unsigned`, `long`,
//         `unsigned long`, `long long`, `unsigned long long`
// *   Enums: printed as their underlying integral value
// *   Floating-point: `float`, `double`, `long double`
//
// However, in the `str_format` library, a format conversion specifies a broader
// C++ conceptual category instead of an exact type. For example, `%s` binds to
// any string-like argument, so `std::string`, `absl::string_view`, and
// `const char*` are all accepted. Likewise, `%d` accepts any integer-like
// argument, etc.

template <typename... Args>
using FormatSpec = str_format_internal::FormatSpecTemplate<
    str_format_internal::ArgumentToConv<Args>()...>;

// ParsedFormat
//
// A `ParsedFormat` is a class template representing a preparsed `FormatSpec`,
// with template arguments specifying the conversion characters used within the
// format string. Such characters must be valid format type specifiers, and
// these type specifiers are checked at compile-time.
//
// Instances of `ParsedFormat` can be created, copied, and reused to speed up
// formatting loops. A `ParsedFormat` may either be constructed statically, or
// dynamically through its `New()` factory function, which only constructs a
// runtime object if the format is valid at that time.
//
// Example:
//
//   // Verified at compile time.
//   absl::ParsedFormat<'s', 'd'> formatString("Welcome to %s, Number %d!");
//   absl::StrFormat(formatString, "TheVillage", 6);
//
//   // Verified at runtime.
//   auto format_runtime = absl::ParsedFormat<'d'>::New(format_string);
//   if (format_runtime) {
//     value = absl::StrFormat(*format_runtime, i);
//   } else {
//     ... error case ...
//   }

#if defined(__cpp_nontype_template_parameter_auto)
// If C++17 is available, an 'extended' format is also allowed that can specify
// multiple conversion characters per format argument, using a combination of
// `absl::FormatConversionCharSet` enum values (logically a set union)
//  via the `|` operator. (Single character-based arguments are still accepted,
// but cannot be combined). Some common conversions also have predefined enum
// values, such as `absl::FormatConversionCharSet::kIntegral`.
//
// Example:
//   // Extended format supports multiple conversion characters per argument,
//   // specified via a combination of `FormatConversionCharSet` enums.
//   using MyFormat = absl::ParsedFormat<absl::FormatConversionCharSet::d |
//                                       absl::FormatConversionCharSet::x>;
//   MyFormat GetFormat(bool use_hex) {
//     if (use_hex) return MyFormat("foo %x bar");
//     return MyFormat("foo %d bar");
//   }
//   // `format` can be used with any value that supports 'd' and 'x',
//   // like `int`.
//   auto format = GetFormat(use_hex);
//   value = StringF(format, i);
template <auto... Conv>
using ParsedFormat = absl::str_format_internal::ExtendedParsedFormat<
    absl::str_format_internal::ToFormatConversionCharSet(Conv)...>;
#else
template <char... Conv>
using ParsedFormat = str_format_internal::ExtendedParsedFormat<
    absl::str_format_internal::ToFormatConversionCharSet(Conv)...>;
#endif  // defined(__cpp_nontype_template_parameter_auto)

// StrFormat()
//
// Returns a `string` given a `printf()`-style format string and zero or more
// additional arguments. Use it as you would `sprintf()`. `StrFormat()` is the
// primary formatting function within the `str_format` library, and should be
// used in most cases where you need type-safe conversion of types into
// formatted strings.
//
// The format string generally consists of ordinary character data along with
// one or more format conversion specifiers (denoted by the `%` character).
// Ordinary character data is returned unchanged into the result string, while
// each conversion specification performs a type substitution from
// `StrFormat()`'s other arguments. See the comments for `FormatSpec` for full
// information on the makeup of this format string.
//
// Example:
//
//   std::string s = absl::StrFormat(
//       "Welcome to %s, Number %d!", "The Village", 6);
//   EXPECT_EQ("Welcome to The Village, Number 6!", s);
//
// Returns an empty string in case of error.
template <typename... Args>
ABSL_MUST_USE_RESULT std::string StrFormat(const FormatSpec<Args...>& format,
                                           const Args&... args) {
  return str_format_internal::FormatPack(
      str_format_internal::UntypedFormatSpecImpl::Extract(format),
      {str_format_internal::FormatArgImpl(args)...});
}

// StrAppendFormat()
//
// Appends to a `dst` string given a format string, and zero or more additional
// arguments, returning `*dst` as a convenience for chaining purposes. Appends
// nothing in case of error (but possibly alters its capacity).
//
// Example:
//
//   std::string orig("For example PI is approximately ");
//   std::cout << StrAppendFormat(&orig, "%12.6f", 3.14);
template <typename... Args>
std::string& StrAppendFormat(std::string* dst,
                             const FormatSpec<Args...>& format,
                             const Args&... args) {
  return str_format_internal::AppendPack(
      dst, str_format_internal::UntypedFormatSpecImpl::Extract(format),
      {str_format_internal::FormatArgImpl(args)...});
}

// StreamFormat()
//
// Writes to an output stream given a format string and zero or more arguments,
// generally in a manner that is more efficient than streaming the result of
// `absl:: StrFormat()`. The returned object must be streamed before the full
// expression ends.
//
// Example:
//
//   std::cout << StreamFormat("%12.6f", 3.14);
template <typename... Args>
ABSL_MUST_USE_RESULT str_format_internal::Streamable StreamFormat(
    const FormatSpec<Args...>& format, const Args&... args) {
  return str_format_internal::Streamable(
      str_format_internal::UntypedFormatSpecImpl::Extract(format),
      {str_format_internal::FormatArgImpl(args)...});
}

// PrintF()
//
// Writes to stdout given a format string and zero or more arguments. This
// function is functionally equivalent to `std::printf()` (and type-safe);
// prefer `absl::PrintF()` over `std::printf()`.
//
// Example:
//
//   std::string_view s = "Ulaanbaatar";
//   absl::PrintF("The capital of Mongolia is %s", s);
//
//   Outputs: "The capital of Mongolia is Ulaanbaatar"
//
template <typename... Args>
int PrintF(const FormatSpec<Args...>& format, const Args&... args) {
  return str_format_internal::FprintF(
      stdout, str_format_internal::UntypedFormatSpecImpl::Extract(format),
      {str_format_internal::FormatArgImpl(args)...});
}

// FPrintF()
//
// Writes to a file given a format string and zero or more arguments. This
// function is functionally equivalent to `std::fprintf()` (and type-safe);
// prefer `absl::FPrintF()` over `std::fprintf()`.
//
// Example:
//
//   std::string_view s = "Ulaanbaatar";
//   absl::FPrintF(stdout, "The capital of Mongolia is %s", s);
//
//   Outputs: "The capital of Mongolia is Ulaanbaatar"
//
template <typename... Args>
int FPrintF(std::FILE* output, const FormatSpec<Args...>& format,
            const Args&... args) {
  return str_format_internal::FprintF(
      output, str_format_internal::UntypedFormatSpecImpl::Extract(format),
      {str_format_internal::FormatArgImpl(args)...});
}

// SNPrintF()
//
// Writes to a sized buffer given a format string and zero or more arguments.
// This function is functionally equivalent to `std::snprintf()` (and
// type-safe); prefer `absl::SNPrintF()` over `std::snprintf()`.
//
// In particular, a successful call to `absl::SNPrintF()` writes at most `size`
// bytes of the formatted output to `output`, including a NUL-terminator, and
// returns the number of bytes that would have been written if truncation did
// not occur. In the event of an error, a negative value is returned and `errno`
// is set.
//
// Example:
//
//   std::string_view s = "Ulaanbaatar";
//   char output[128];
//   absl::SNPrintF(output, sizeof(output),
//                  "The capital of Mongolia is %s", s);
//
//   Post-condition: output == "The capital of Mongolia is Ulaanbaatar"
//
template <typename... Args>
int SNPrintF(char* output, std::size_t size, const FormatSpec<Args...>& format,
             const Args&... args) {
  return str_format_internal::SnprintF(
      output, size, str_format_internal::UntypedFormatSpecImpl::Extract(format),
      {str_format_internal::FormatArgImpl(args)...});
}

// -----------------------------------------------------------------------------
// Custom Output Formatting Functions
// -----------------------------------------------------------------------------

// FormatRawSink
//
// FormatRawSink is a type erased wrapper around arbitrary sink objects
// specifically used as an argument to `Format()`.
//
// All the object has to do define an overload of `AbslFormatFlush()` for the
// sink, usually by adding a ADL-based free function in the same namespace as
// the sink:
//
//   void AbslFormatFlush(MySink* dest, absl::string_view part);
//
// where `dest` is the pointer passed to `absl::Format()`. The function should
// append `part` to `dest`.
//
// FormatRawSink does not own the passed sink object. The passed object must
// outlive the FormatRawSink.
class FormatRawSink {
 public:
  // Implicitly convert from any type that provides the hook function as
  // described above.
  template <typename T,
            typename = typename std::enable_if<std::is_constructible<
                str_format_internal::FormatRawSinkImpl, T*>::value>::type>
  FormatRawSink(T* raw)  // NOLINT
      : sink_(raw) {}

 private:
  friend str_format_internal::FormatRawSinkImpl;
  str_format_internal::FormatRawSinkImpl sink_;
};

// Format()
//
// Writes a formatted string to an arbitrary sink object (implementing the
// `absl::FormatRawSink` interface), using a format string and zero or more
// additional arguments.
//
// By default, `std::string`, `std::ostream`, and `absl::Cord` are supported as
// destination objects. If a `std::string` is used the formatted string is
// appended to it.
//
// `absl::Format()` is a generic version of `absl::StrAppendFormat()`, for
// custom sinks. The format string, like format strings for `StrFormat()`, is
// checked at compile-time.
//
// On failure, this function returns `false` and the state of the sink is
// unspecified.
template <typename... Args>
bool Format(FormatRawSink raw_sink, const FormatSpec<Args...>& format,
            const Args&... args) {
  return str_format_internal::FormatUntyped(
      str_format_internal::FormatRawSinkImpl::Extract(raw_sink),
      str_format_internal::UntypedFormatSpecImpl::Extract(format),
      {str_format_internal::FormatArgImpl(args)...});
}

// FormatArg
//
// A type-erased handle to a format argument specifically used as an argument to
// `FormatUntyped()`. You may construct `FormatArg` by passing
// reference-to-const of any printable type. `FormatArg` is both copyable and
// assignable. The source data must outlive the `FormatArg` instance. See
// example below.
//
using FormatArg = str_format_internal::FormatArgImpl;

// FormatUntyped()
//
// Writes a formatted string to an arbitrary sink object (implementing the
// `absl::FormatRawSink` interface), using an `UntypedFormatSpec` and zero or
// more additional arguments.
//
// This function acts as the most generic formatting function in the
// `str_format` library. The caller provides a raw sink, an unchecked format
// string, and (usually) a runtime specified list of arguments; no compile-time
// checking of formatting is performed within this function. As a result, a
// caller should check the return value to verify that no error occurred.
// On failure, this function returns `false` and the state of the sink is
// unspecified.
//
// The arguments are provided in an `absl::Span<const absl::FormatArg>`.
// Each `absl::FormatArg` object binds to a single argument and keeps a
// reference to it. The values used to create the `FormatArg` objects must
// outlive this function call.
//
// Example:
//
//   std::optional<std::string> FormatDynamic(
//       const std::string& in_format,
//       const vector<std::string>& in_args) {
//     std::string out;
//     std::vector<absl::FormatArg> args;
//     for (const auto& v : in_args) {
//       // It is important that 'v' is a reference to the objects in in_args.
//       // The values we pass to FormatArg must outlive the call to
//       // FormatUntyped.
//       args.emplace_back(v);
//     }
//     absl::UntypedFormatSpec format(in_format);
//     if (!absl::FormatUntyped(&out, format, args)) {
//       return std::nullopt;
//     }
//     return std::move(out);
//   }
//
ABSL_MUST_USE_RESULT inline bool FormatUntyped(
    FormatRawSink raw_sink, const UntypedFormatSpec& format,
    absl::Span<const FormatArg> args) {
  return str_format_internal::FormatUntyped(
      str_format_internal::FormatRawSinkImpl::Extract(raw_sink),
      str_format_internal::UntypedFormatSpecImpl::Extract(format), args);
}

//------------------------------------------------------------------------------
// StrFormat Extensions
//------------------------------------------------------------------------------
//
// AbslStringify()
//
// A simpler customization API for formatting user-defined types using
// absl::StrFormat(). The API relies on detecting an overload in the
// user-defined type's namespace of a free (non-member) `AbslStringify()`
// function as a friend definition with the following signature:
//
// template <typename Sink>
// void AbslStringify(Sink& sink, const X& value);
//
// An `AbslStringify()` overload for a type should only be declared in the same
// file and namespace as said type.
//
// Note that unlike with AbslFormatConvert(), AbslStringify() does not allow
// customization of allowed conversion characters. AbslStringify() uses `%v` as
// the underlying conversion specififer. Additionally, AbslStringify() supports
// use with absl::StrCat while AbslFormatConvert() does not.
//
// Example:
//
// struct Point {
//   // To add formatting support to `Point`, we simply need to add a free
//   // (non-member) function `AbslStringify()`. This method prints in the
//   // request format using the underlying `%v` specifier. You can add such a
//   // free function using a friend declaration within the body of the class.
//   // The sink parameter is a templated type to avoid requiring dependencies.
//   template <typename Sink>
//   friend void AbslStringify(Sink& sink, const Point& p) {
//     absl::Format(&sink, "(%v, %v)", p.x, p.y);
//   }
//
//   int x;
//   int y;
// };
//
// AbslFormatConvert()
//
// The StrFormat library provides a customization API for formatting
// user-defined types using absl::StrFormat(). The API relies on detecting an
// overload in the user-defined type's namespace of a free (non-member)
// `AbslFormatConvert()` function, usually as a friend definition with the
// following signature:
//
// absl::FormatConvertResult<...> AbslFormatConvert(
//     const X& value,
//     const absl::FormatConversionSpec& spec,
//     absl::FormatSink *sink);
//
// An `AbslFormatConvert()` overload for a type should only be declared in the
// same file and namespace as said type.
//
// The abstractions within this definition include:
//
// * An `absl::FormatConversionSpec` to specify the fields to pull from a
//   user-defined type's format string
// * An `absl::FormatSink` to hold the converted string data during the
//   conversion process.
// * An `absl::FormatConvertResult` to hold the status of the returned
//   formatting operation
//
// The return type encodes all the conversion characters that your
// AbslFormatConvert() routine accepts.  The return value should be {true}.
// A return value of {false} will result in `StrFormat()` returning
// an empty string.  This result will be propagated to the result of
// `FormatUntyped`.
//
// Example:
//
// struct Point {
//   // To add formatting support to `Point`, we simply need to add a free
//   // (non-member) function `AbslFormatConvert()`.  This method interprets
//   // `spec` to print in the request format. The allowed conversion characters
//   // can be restricted via the type of the result, in this example
//   // string and integral formatting are allowed (but not, for instance
//   // floating point characters like "%f").  You can add such a free function
//   // using a friend declaration within the body of the class:
//   friend absl::FormatConvertResult<absl::FormatConversionCharSet::kString |
//                                    absl::FormatConversionCharSet::kIntegral>
//   AbslFormatConvert(const Point& p, const absl::FormatConversionSpec& spec,
//                     absl::FormatSink* s) {
//     if (spec.conversion_char() == absl::FormatConversionChar::s) {
//       absl::Format(s, "x=%vy=%v", p.x, p.y);
//     } else {
//       absl::Format(s, "%v,%v", p.x, p.y);
//     }
//     return {true};
//   }
//
//   int x;
//   int y;
// };

// clang-format off

// FormatConversionChar
//
// Specifies the formatting character provided in the format string
// passed to `StrFormat()`.
enum class FormatConversionChar : uint8_t {
  c, s,                    // text
  d, i, o, u, x, X,        // int
  f, F, e, E, g, G, a, A,  // float
  n, p, v                  // misc
};
// clang-format on

// FormatConversionSpec
//
// Specifies modifications to the conversion of the format string, through use
// of one or more format flags in the source format string.
class FormatConversionSpec {
 public:
  // FormatConversionSpec::is_basic()
  //
  // Indicates that width and precision are not specified, and no additional
  // flags are set for this conversion character in the format string.
  bool is_basic() const { return impl_.is_basic(); }

  // FormatConversionSpec::has_left_flag()
  //
  // Indicates whether the result should be left justified for this conversion
  // character in the format string. This flag is set through use of a '-'
  // character in the format string. E.g. "%-s"
  bool has_left_flag() const { return impl_.has_left_flag(); }

  // FormatConversionSpec::has_show_pos_flag()
  //
  // Indicates whether a sign column is prepended to the result for this
  // conversion character in the format string, even if the result is positive.
  // This flag is set through use of a '+' character in the format string.
  // E.g. "%+d"
  bool has_show_pos_flag() const { return impl_.has_show_pos_flag(); }

  // FormatConversionSpec::has_sign_col_flag()
  //
  // Indicates whether a mandatory sign column is added to the result for this
  // conversion character. This flag is set through use of a space character
  // (' ') in the format string. E.g. "% i"
  bool has_sign_col_flag() const { return impl_.has_sign_col_flag(); }

  // FormatConversionSpec::has_alt_flag()
  //
  // Indicates whether an "alternate" format is applied to the result for this
  // conversion character. Alternative forms depend on the type of conversion
  // character, and unallowed alternatives are undefined. This flag is set
  // through use of a '#' character in the format string. E.g. "%#h"
  bool has_alt_flag() const { return impl_.has_alt_flag(); }

  // FormatConversionSpec::has_zero_flag()
  //
  // Indicates whether zeroes should be prepended to the result for this
  // conversion character instead of spaces. This flag is set through use of the
  // '0' character in the format string. E.g. "%0f"
  bool has_zero_flag() const { return impl_.has_zero_flag(); }

  // FormatConversionSpec::conversion_char()
  //
  // Returns the underlying conversion character.
  FormatConversionChar conversion_char() const {
    return impl_.conversion_char();
  }

  // FormatConversionSpec::width()
  //
  // Returns the specified width (indicated through use of a non-zero integer
  // value or '*' character) of the conversion character. If width is
  // unspecified, it returns a negative value.
  int width() const { return impl_.width(); }

  // FormatConversionSpec::precision()
  //
  // Returns the specified precision (through use of the '.' character followed
  // by a non-zero integer value or '*' character) of the conversion character.
  // If precision is unspecified, it returns a negative value.
  int precision() const { return impl_.precision(); }

 private:
  explicit FormatConversionSpec(
      str_format_internal::FormatConversionSpecImpl impl)
      : impl_(impl) {}

  friend str_format_internal::FormatConversionSpecImpl;

  absl::str_format_internal::FormatConversionSpecImpl impl_;
};

// Type safe OR operator for FormatConversionCharSet to allow accepting multiple
// conversion chars in custom format converters.
constexpr FormatConversionCharSet operator|(FormatConversionCharSet a,
                                            FormatConversionCharSet b) {
  return static_cast<FormatConversionCharSet>(static_cast<uint64_t>(a) |
                                              static_cast<uint64_t>(b));
}

// FormatConversionCharSet
//
// Specifies the _accepted_ conversion types as a template parameter to
// FormatConvertResult for custom implementations of `AbslFormatConvert`.
// Note the helper predefined alias definitions (kIntegral, etc.) below.
enum class FormatConversionCharSet : uint64_t {
  // text
  c = str_format_internal::FormatConversionCharToConvInt('c'),
  s = str_format_internal::FormatConversionCharToConvInt('s'),
  // integer
  d = str_format_internal::FormatConversionCharToConvInt('d'),
  i = str_format_internal::FormatConversionCharToConvInt('i'),
  o = str_format_internal::FormatConversionCharToConvInt('o'),
  u = str_format_internal::FormatConversionCharToConvInt('u'),
  x = str_format_internal::FormatConversionCharToConvInt('x'),
  X = str_format_internal::FormatConversionCharToConvInt('X'),
  // Float
  f = str_format_internal::FormatConversionCharToConvInt('f'),
  F = str_format_internal::FormatConversionCharToConvInt('F'),
  e = str_format_internal::FormatConversionCharToConvInt('e'),
  E = str_format_internal::FormatConversionCharToConvInt('E'),
  g = str_format_internal::FormatConversionCharToConvInt('g'),
  G = str_format_internal::FormatConversionCharToConvInt('G'),
  a = str_format_internal::FormatConversionCharToConvInt('a'),
  A = str_format_internal::FormatConversionCharToConvInt('A'),
  // misc
  n = str_format_internal::FormatConversionCharToConvInt('n'),
  p = str_format_internal::FormatConversionCharToConvInt('p'),
  v = str_format_internal::FormatConversionCharToConvInt('v'),

  // Used for width/precision '*' specification.
  kStar = static_cast<uint64_t>(
      absl::str_format_internal::FormatConversionCharSetInternal::kStar),
  // Some predefined values:
  kIntegral = d | i | u | o | x | X,
  kFloating = a | e | f | g | A | E | F | G,
  kNumeric = kIntegral | kFloating,
  kString = s,
  kPointer = p,
};

// FormatSink
//
// A format sink is a generic abstraction to which conversions may write their
// formatted string data. `absl::FormatConvert()` uses this sink to write its
// formatted string.
//
class FormatSink {
 public:
  // FormatSink::Append()
  //
  // Appends `count` copies of `ch` to the format sink.
  void Append(size_t count, char ch) { sink_->Append(count, ch); }

  // Overload of FormatSink::Append() for appending the characters of a string
  // view to a format sink.
  void Append(string_view v) { sink_->Append(v); }

  // FormatSink::PutPaddedString()
  //
  // Appends `precision` number of bytes of `v` to the format sink. If this is
  // less than `width`, spaces will be appended first (if `left` is false), or
  // after (if `left` is true) to ensure the total amount appended is
  // at least `width`.
  bool PutPaddedString(string_view v, int width, int precision, bool left) {
    return sink_->PutPaddedString(v, width, precision, left);
  }

  // Support `absl::Format(&sink, format, args...)`.
  friend void AbslFormatFlush(FormatSink* sink, absl::string_view v) {
    sink->Append(v);
  }

 private:
  friend str_format_internal::FormatSinkImpl;
  explicit FormatSink(str_format_internal::FormatSinkImpl* s) : sink_(s) {}
  str_format_internal::FormatSinkImpl* sink_;
};

// FormatConvertResult
//
// Indicates whether a call to AbslFormatConvert() was successful.
// This return type informs the StrFormat extension framework (through
// ADL but using the return type) of what conversion characters are supported.
// It is strongly discouraged to return {false}, as this will result in an
// empty string in StrFormat.
template <FormatConversionCharSet C>
struct FormatConvertResult {
  bool value;
};

ABSL_NAMESPACE_END
}  // namespace absl

#endif  // ABSL_STRINGS_STR_FORMAT_H_