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1 // Formatting library for C++ - experimental format string compilation
2 //
3 // Copyright (c) 2012 - present, Victor Zverovich and fmt contributors
4 // All rights reserved.
5 //
6 // For the license information refer to format.h.
7 
8 #ifndef FMT_COMPILE_H_
9 #define FMT_COMPILE_H_
10 
11 #include <vector>
12 
13 #include "format.h"
14 
15 FMT_BEGIN_NAMESPACE
16 namespace detail {
17 
18 // A compile-time string which is compiled into fast formatting code.
19 class compiled_string {};
20 
21 template <typename S>
22 struct is_compiled_string : std::is_base_of<compiled_string, S> {};
23 
24 /**
25   \rst
26   Converts a string literal *s* into a format string that will be parsed at
27   compile time and converted into efficient formatting code. Requires C++17
28   ``constexpr if`` compiler support.
29 
30   **Example**::
31 
32     // Converts 42 into std::string using the most efficient method and no
33     // runtime format string processing.
34     std::string s = fmt::format(FMT_COMPILE("{}"), 42);
35   \endrst
36  */
37 #define FMT_COMPILE(s) FMT_STRING_IMPL(s, fmt::detail::compiled_string)
38 
39 template <typename T, typename... Tail>
first(const T & value,const Tail &...)40 const T& first(const T& value, const Tail&...) {
41   return value;
42 }
43 
44 // Part of a compiled format string. It can be either literal text or a
45 // replacement field.
46 template <typename Char> struct format_part {
47   enum class kind { arg_index, arg_name, text, replacement };
48 
49   struct replacement {
50     arg_ref<Char> arg_id;
51     dynamic_format_specs<Char> specs;
52   };
53 
54   kind part_kind;
55   union value {
56     int arg_index;
57     basic_string_view<Char> str;
58     replacement repl;
59 
arg_index(index)60     FMT_CONSTEXPR value(int index = 0) : arg_index(index) {}
value(basic_string_view<Char> s)61     FMT_CONSTEXPR value(basic_string_view<Char> s) : str(s) {}
value(replacement r)62     FMT_CONSTEXPR value(replacement r) : repl(r) {}
63   } val;
64   // Position past the end of the argument id.
65   const Char* arg_id_end = nullptr;
66 
67   FMT_CONSTEXPR format_part(kind k = kind::arg_index, value v = {})
part_kindformat_part68       : part_kind(k), val(v) {}
69 
make_arg_indexformat_part70   static FMT_CONSTEXPR format_part make_arg_index(int index) {
71     return format_part(kind::arg_index, index);
72   }
make_arg_nameformat_part73   static FMT_CONSTEXPR format_part make_arg_name(basic_string_view<Char> name) {
74     return format_part(kind::arg_name, name);
75   }
make_textformat_part76   static FMT_CONSTEXPR format_part make_text(basic_string_view<Char> text) {
77     return format_part(kind::text, text);
78   }
make_replacementformat_part79   static FMT_CONSTEXPR format_part make_replacement(replacement repl) {
80     return format_part(kind::replacement, repl);
81   }
82 };
83 
84 template <typename Char> struct part_counter {
85   unsigned num_parts = 0;
86 
on_textpart_counter87   FMT_CONSTEXPR void on_text(const Char* begin, const Char* end) {
88     if (begin != end) ++num_parts;
89   }
90 
on_arg_idpart_counter91   FMT_CONSTEXPR int on_arg_id() { return ++num_parts, 0; }
on_arg_idpart_counter92   FMT_CONSTEXPR int on_arg_id(int) { return ++num_parts, 0; }
on_arg_idpart_counter93   FMT_CONSTEXPR int on_arg_id(basic_string_view<Char>) {
94     return ++num_parts, 0;
95   }
96 
on_replacement_fieldpart_counter97   FMT_CONSTEXPR void on_replacement_field(int, const Char*) {}
98 
on_format_specspart_counter99   FMT_CONSTEXPR const Char* on_format_specs(int, const Char* begin,
100                                             const Char* end) {
101     // Find the matching brace.
102     unsigned brace_counter = 0;
103     for (; begin != end; ++begin) {
104       if (*begin == '{') {
105         ++brace_counter;
106       } else if (*begin == '}') {
107         if (brace_counter == 0u) break;
108         --brace_counter;
109       }
110     }
111     return begin;
112   }
113 
on_errorpart_counter114   FMT_CONSTEXPR void on_error(const char*) {}
115 };
116 
117 // Counts the number of parts in a format string.
118 template <typename Char>
count_parts(basic_string_view<Char> format_str)119 FMT_CONSTEXPR unsigned count_parts(basic_string_view<Char> format_str) {
120   part_counter<Char> counter;
121   parse_format_string<true>(format_str, counter);
122   return counter.num_parts;
123 }
124 
125 template <typename Char, typename PartHandler>
126 class format_string_compiler : public error_handler {
127  private:
128   using part = format_part<Char>;
129 
130   PartHandler handler_;
131   part part_;
132   basic_string_view<Char> format_str_;
133   basic_format_parse_context<Char> parse_context_;
134 
135  public:
format_string_compiler(basic_string_view<Char> format_str,PartHandler handler)136   FMT_CONSTEXPR format_string_compiler(basic_string_view<Char> format_str,
137                                        PartHandler handler)
138       : handler_(handler),
139         format_str_(format_str),
140         parse_context_(format_str) {}
141 
on_text(const Char * begin,const Char * end)142   FMT_CONSTEXPR void on_text(const Char* begin, const Char* end) {
143     if (begin != end)
144       handler_(part::make_text({begin, to_unsigned(end - begin)}));
145   }
146 
on_arg_id()147   FMT_CONSTEXPR int on_arg_id() {
148     part_ = part::make_arg_index(parse_context_.next_arg_id());
149     return 0;
150   }
151 
on_arg_id(int id)152   FMT_CONSTEXPR int on_arg_id(int id) {
153     parse_context_.check_arg_id(id);
154     part_ = part::make_arg_index(id);
155     return 0;
156   }
157 
on_arg_id(basic_string_view<Char> id)158   FMT_CONSTEXPR int on_arg_id(basic_string_view<Char> id) {
159     part_ = part::make_arg_name(id);
160     return 0;
161   }
162 
on_replacement_field(int,const Char * ptr)163   FMT_CONSTEXPR void on_replacement_field(int, const Char* ptr) {
164     part_.arg_id_end = ptr;
165     handler_(part_);
166   }
167 
on_format_specs(int,const Char * begin,const Char * end)168   FMT_CONSTEXPR const Char* on_format_specs(int, const Char* begin,
169                                             const Char* end) {
170     auto repl = typename part::replacement();
171     dynamic_specs_handler<basic_format_parse_context<Char>> handler(
172         repl.specs, parse_context_);
173     auto it = parse_format_specs(begin, end, handler);
174     if (*it != '}') on_error("missing '}' in format string");
175     repl.arg_id = part_.part_kind == part::kind::arg_index
176                       ? arg_ref<Char>(part_.val.arg_index)
177                       : arg_ref<Char>(part_.val.str);
178     auto part = part::make_replacement(repl);
179     part.arg_id_end = begin;
180     handler_(part);
181     return it;
182   }
183 };
184 
185 // Compiles a format string and invokes handler(part) for each parsed part.
186 template <bool IS_CONSTEXPR, typename Char, typename PartHandler>
compile_format_string(basic_string_view<Char> format_str,PartHandler handler)187 FMT_CONSTEXPR void compile_format_string(basic_string_view<Char> format_str,
188                                          PartHandler handler) {
189   parse_format_string<IS_CONSTEXPR>(
190       format_str,
191       format_string_compiler<Char, PartHandler>(format_str, handler));
192 }
193 
194 template <typename OutputIt, typename Context, typename Id>
format_arg(basic_format_parse_context<typename Context::char_type> & parse_ctx,Context & ctx,Id arg_id)195 void format_arg(
196     basic_format_parse_context<typename Context::char_type>& parse_ctx,
197     Context& ctx, Id arg_id) {
198   ctx.advance_to(visit_format_arg(
199       arg_formatter<OutputIt, typename Context::char_type>(ctx, &parse_ctx),
200       ctx.arg(arg_id)));
201 }
202 
203 // vformat_to is defined in a subnamespace to prevent ADL.
204 namespace cf {
205 template <typename Context, typename OutputIt, typename CompiledFormat>
206 auto vformat_to(OutputIt out, CompiledFormat& cf,
207                 basic_format_args<Context> args) -> typename Context::iterator {
208   using char_type = typename Context::char_type;
209   basic_format_parse_context<char_type> parse_ctx(
210       to_string_view(cf.format_str_));
211   Context ctx(out, args);
212 
213   const auto& parts = cf.parts();
214   for (auto part_it = std::begin(parts); part_it != std::end(parts);
215        ++part_it) {
216     const auto& part = *part_it;
217     const auto& value = part.val;
218 
219     using format_part_t = format_part<char_type>;
220     switch (part.part_kind) {
221     case format_part_t::kind::text: {
222       const auto text = value.str;
223       auto output = ctx.out();
224       auto&& it = reserve(output, text.size());
225       it = std::copy_n(text.begin(), text.size(), it);
226       ctx.advance_to(output);
227       break;
228     }
229 
230     case format_part_t::kind::arg_index:
231       advance_to(parse_ctx, part.arg_id_end);
232       detail::format_arg<OutputIt>(parse_ctx, ctx, value.arg_index);
233       break;
234 
235     case format_part_t::kind::arg_name:
236       advance_to(parse_ctx, part.arg_id_end);
237       detail::format_arg<OutputIt>(parse_ctx, ctx, value.str);
238       break;
239 
240     case format_part_t::kind::replacement: {
241       const auto& arg_id_value = value.repl.arg_id.val;
242       const auto arg = value.repl.arg_id.kind == arg_id_kind::index
243                            ? ctx.arg(arg_id_value.index)
244                            : ctx.arg(arg_id_value.name);
245 
246       auto specs = value.repl.specs;
247 
248       handle_dynamic_spec<width_checker>(specs.width, specs.width_ref, ctx);
249       handle_dynamic_spec<precision_checker>(specs.precision,
250                                              specs.precision_ref, ctx);
251 
252       error_handler h;
253       numeric_specs_checker<error_handler> checker(h, arg.type());
254       if (specs.align == align::numeric) checker.require_numeric_argument();
255       if (specs.sign != sign::none) checker.check_sign();
256       if (specs.alt) checker.require_numeric_argument();
257       if (specs.precision >= 0) checker.check_precision();
258 
259       advance_to(parse_ctx, part.arg_id_end);
260       ctx.advance_to(
261           visit_format_arg(arg_formatter<OutputIt, typename Context::char_type>(
262                                ctx, nullptr, &specs),
263                            arg));
264       break;
265     }
266     }
267   }
268   return ctx.out();
269 }
270 }  // namespace cf
271 
272 struct basic_compiled_format {};
273 
274 template <typename S, typename = void>
275 struct compiled_format_base : basic_compiled_format {
276   using char_type = char_t<S>;
277   using parts_container = std::vector<detail::format_part<char_type>>;
278 
279   parts_container compiled_parts;
280 
compiled_format_basecompiled_format_base281   explicit compiled_format_base(basic_string_view<char_type> format_str) {
282     compile_format_string<false>(format_str,
283                                  [this](const format_part<char_type>& part) {
284                                    compiled_parts.push_back(part);
285                                  });
286   }
287 
partscompiled_format_base288   const parts_container& parts() const { return compiled_parts; }
289 };
290 
291 template <typename Char, unsigned N> struct format_part_array {
292   format_part<Char> data[N] = {};
293   FMT_CONSTEXPR format_part_array() = default;
294 };
295 
296 template <typename Char, unsigned N>
compile_to_parts(basic_string_view<Char> format_str)297 FMT_CONSTEXPR format_part_array<Char, N> compile_to_parts(
298     basic_string_view<Char> format_str) {
299   format_part_array<Char, N> parts;
300   unsigned counter = 0;
301   // This is not a lambda for compatibility with older compilers.
302   struct {
303     format_part<Char>* parts;
304     unsigned* counter;
305     FMT_CONSTEXPR void operator()(const format_part<Char>& part) {
306       parts[(*counter)++] = part;
307     }
308   } collector{parts.data, &counter};
309   compile_format_string<true>(format_str, collector);
310   if (counter < N) {
311     parts.data[counter] =
312         format_part<Char>::make_text(basic_string_view<Char>());
313   }
314   return parts;
315 }
316 
constexpr_max(const T & a,const T & b)317 template <typename T> constexpr const T& constexpr_max(const T& a, const T& b) {
318   return (a < b) ? b : a;
319 }
320 
321 template <typename S>
322 struct compiled_format_base<S, enable_if_t<is_compile_string<S>::value>>
323     : basic_compiled_format {
324   using char_type = char_t<S>;
325 
326   FMT_CONSTEXPR explicit compiled_format_base(basic_string_view<char_type>) {}
327 
328 // Workaround for old compilers. Format string compilation will not be
329 // performed there anyway.
330 #if FMT_USE_CONSTEXPR
331   static FMT_CONSTEXPR_DECL const unsigned num_format_parts =
332       constexpr_max(count_parts(to_string_view(S())), 1u);
333 #else
334   static const unsigned num_format_parts = 1;
335 #endif
336 
337   using parts_container = format_part<char_type>[num_format_parts];
338 
339   const parts_container& parts() const {
340     static FMT_CONSTEXPR_DECL const auto compiled_parts =
341         compile_to_parts<char_type, num_format_parts>(
342             detail::to_string_view(S()));
343     return compiled_parts.data;
344   }
345 };
346 
347 template <typename S, typename... Args>
348 class compiled_format : private compiled_format_base<S> {
349  public:
350   using typename compiled_format_base<S>::char_type;
351 
352  private:
353   basic_string_view<char_type> format_str_;
354 
355   template <typename Context, typename OutputIt, typename CompiledFormat>
356   friend auto cf::vformat_to(OutputIt out, CompiledFormat& cf,
357                              basic_format_args<Context> args) ->
358       typename Context::iterator;
359 
360  public:
361   compiled_format() = delete;
362   explicit constexpr compiled_format(basic_string_view<char_type> format_str)
363       : compiled_format_base<S>(format_str), format_str_(format_str) {}
364 };
365 
366 #ifdef __cpp_if_constexpr
367 template <typename... Args> struct type_list {};
368 
369 // Returns a reference to the argument at index N from [first, rest...].
370 template <int N, typename T, typename... Args>
371 constexpr const auto& get([[maybe_unused]] const T& first,
372                           [[maybe_unused]] const Args&... rest) {
373   static_assert(N < 1 + sizeof...(Args), "index is out of bounds");
374   if constexpr (N == 0)
375     return first;
376   else
377     return get<N - 1>(rest...);
378 }
379 
380 template <int N, typename> struct get_type_impl;
381 
382 template <int N, typename... Args> struct get_type_impl<N, type_list<Args...>> {
383   using type = remove_cvref_t<decltype(get<N>(std::declval<Args>()...))>;
384 };
385 
386 template <int N, typename T>
387 using get_type = typename get_type_impl<N, T>::type;
388 
389 template <typename T> struct is_compiled_format : std::false_type {};
390 
391 template <typename Char> struct text {
392   basic_string_view<Char> data;
393   using char_type = Char;
394 
395   template <typename OutputIt, typename... Args>
396   OutputIt format(OutputIt out, const Args&...) const {
397     return write<Char>(out, data);
398   }
399 };
400 
401 template <typename Char>
402 struct is_compiled_format<text<Char>> : std::true_type {};
403 
404 template <typename Char>
405 constexpr text<Char> make_text(basic_string_view<Char> s, size_t pos,
406                                size_t size) {
407   return {{&s[pos], size}};
408 }
409 
410 template <typename Char> struct code_unit {
411   Char value;
412   using char_type = Char;
413 
414   template <typename OutputIt, typename... Args>
415   OutputIt format(OutputIt out, const Args&...) const {
416     return write<Char>(out, value);
417   }
418 };
419 
420 template <typename Char>
421 struct is_compiled_format<code_unit<Char>> : std::true_type {};
422 
423 // A replacement field that refers to argument N.
424 template <typename Char, typename T, int N> struct field {
425   using char_type = Char;
426 
427   template <typename OutputIt, typename... Args>
428   OutputIt format(OutputIt out, const Args&... args) const {
429     // This ensures that the argument type is convertile to `const T&`.
430     const T& arg = get<N>(args...);
431     return write<Char>(out, arg);
432   }
433 };
434 
435 template <typename Char, typename T, int N>
436 struct is_compiled_format<field<Char, T, N>> : std::true_type {};
437 
438 // A replacement field that refers to argument N and has format specifiers.
439 template <typename Char, typename T, int N> struct spec_field {
440   using char_type = Char;
441   mutable formatter<T, Char> fmt;
442 
443   template <typename OutputIt, typename... Args>
444   OutputIt format(OutputIt out, const Args&... args) const {
445     // This ensures that the argument type is convertile to `const T&`.
446     const T& arg = get<N>(args...);
447     const auto& vargs =
448         make_format_args<basic_format_context<OutputIt, Char>>(args...);
449     basic_format_context<OutputIt, Char> ctx(out, vargs);
450     return fmt.format(arg, ctx);
451   }
452 };
453 
454 template <typename Char, typename T, int N>
455 struct is_compiled_format<spec_field<Char, T, N>> : std::true_type {};
456 
457 template <typename L, typename R> struct concat {
458   L lhs;
459   R rhs;
460   using char_type = typename L::char_type;
461 
462   template <typename OutputIt, typename... Args>
463   OutputIt format(OutputIt out, const Args&... args) const {
464     out = lhs.format(out, args...);
465     return rhs.format(out, args...);
466   }
467 };
468 
469 template <typename L, typename R>
470 struct is_compiled_format<concat<L, R>> : std::true_type {};
471 
472 template <typename L, typename R>
473 constexpr concat<L, R> make_concat(L lhs, R rhs) {
474   return {lhs, rhs};
475 }
476 
477 struct unknown_format {};
478 
479 template <typename Char>
480 constexpr size_t parse_text(basic_string_view<Char> str, size_t pos) {
481   for (size_t size = str.size(); pos != size; ++pos) {
482     if (str[pos] == '{' || str[pos] == '}') break;
483   }
484   return pos;
485 }
486 
487 template <typename Args, size_t POS, int ID, typename S>
488 constexpr auto compile_format_string(S format_str);
489 
490 template <typename Args, size_t POS, int ID, typename T, typename S>
491 constexpr auto parse_tail(T head, S format_str) {
492   if constexpr (POS !=
493                 basic_string_view<typename S::char_type>(format_str).size()) {
494     constexpr auto tail = compile_format_string<Args, POS, ID>(format_str);
495     if constexpr (std::is_same<remove_cvref_t<decltype(tail)>,
496                                unknown_format>())
497       return tail;
498     else
499       return make_concat(head, tail);
500   } else {
501     return head;
502   }
503 }
504 
505 template <typename T, typename Char> struct parse_specs_result {
506   formatter<T, Char> fmt;
507   size_t end;
508   int next_arg_id;
509 };
510 
511 template <typename T, typename Char>
512 constexpr parse_specs_result<T, Char> parse_specs(basic_string_view<Char> str,
513                                                   size_t pos, int arg_id) {
514   str.remove_prefix(pos);
515   auto ctx = basic_format_parse_context<Char>(str, {}, arg_id + 1);
516   auto f = formatter<T, Char>();
517   auto end = f.parse(ctx);
518   return {f, pos + (end - str.data()) + 1, ctx.next_arg_id()};
519 }
520 
521 // Compiles a non-empty format string and returns the compiled representation
522 // or unknown_format() on unrecognized input.
523 template <typename Args, size_t POS, int ID, typename S>
524 constexpr auto compile_format_string(S format_str) {
525   using char_type = typename S::char_type;
526   constexpr basic_string_view<char_type> str = format_str;
527   if constexpr (str[POS] == '{') {
528     if (POS + 1 == str.size())
529       throw format_error("unmatched '{' in format string");
530     if constexpr (str[POS + 1] == '{') {
531       return parse_tail<Args, POS + 2, ID>(make_text(str, POS, 1), format_str);
532     } else if constexpr (str[POS + 1] == '}') {
533       using type = get_type<ID, Args>;
534       return parse_tail<Args, POS + 2, ID + 1>(field<char_type, type, ID>(),
535                                                format_str);
536     } else if constexpr (str[POS + 1] == ':') {
537       using type = get_type<ID, Args>;
538       constexpr auto result = parse_specs<type>(str, POS + 2, ID);
539       return parse_tail<Args, result.end, result.next_arg_id>(
540           spec_field<char_type, type, ID>{result.fmt}, format_str);
541     } else {
542       return unknown_format();
543     }
544   } else if constexpr (str[POS] == '}') {
545     if (POS + 1 == str.size())
546       throw format_error("unmatched '}' in format string");
547     return parse_tail<Args, POS + 2, ID>(make_text(str, POS, 1), format_str);
548   } else {
549     constexpr auto end = parse_text(str, POS + 1);
550     if constexpr (end - POS > 1) {
551       return parse_tail<Args, end, ID>(make_text(str, POS, end - POS),
552                                        format_str);
553     } else {
554       return parse_tail<Args, end, ID>(code_unit<char_type>{str[POS]},
555                                        format_str);
556     }
557   }
558 }
559 
560 template <typename... Args, typename S,
561           FMT_ENABLE_IF(is_compile_string<S>::value ||
562                         detail::is_compiled_string<S>::value)>
563 constexpr auto compile(S format_str) {
564   constexpr basic_string_view<typename S::char_type> str = format_str;
565   if constexpr (str.size() == 0) {
566     return detail::make_text(str, 0, 0);
567   } else {
568     constexpr auto result =
569         detail::compile_format_string<detail::type_list<Args...>, 0, 0>(
570             format_str);
571     if constexpr (std::is_same<remove_cvref_t<decltype(result)>,
572                                detail::unknown_format>()) {
573       return detail::compiled_format<S, Args...>(to_string_view(format_str));
574     } else {
575       return result;
576     }
577   }
578 }
579 #else
580 template <typename... Args, typename S,
581           FMT_ENABLE_IF(is_compile_string<S>::value)>
582 constexpr auto compile(S format_str) -> detail::compiled_format<S, Args...> {
583   return detail::compiled_format<S, Args...>(to_string_view(format_str));
584 }
585 #endif  // __cpp_if_constexpr
586 
587 // Compiles the format string which must be a string literal.
588 template <typename... Args, typename Char, size_t N>
589 auto compile(const Char (&format_str)[N])
590     -> detail::compiled_format<const Char*, Args...> {
591   return detail::compiled_format<const Char*, Args...>(
592       basic_string_view<Char>(format_str, N - 1));
593 }
594 }  // namespace detail
595 
596 // DEPRECATED! use FMT_COMPILE instead.
597 template <typename... Args>
598 FMT_DEPRECATED auto compile(const Args&... args)
599     -> decltype(detail::compile(args...)) {
600   return detail::compile(args...);
601 }
602 
603 #if FMT_USE_CONSTEXPR
604 #  ifdef __cpp_if_constexpr
605 
606 template <typename CompiledFormat, typename... Args,
607           typename Char = typename CompiledFormat::char_type,
608           FMT_ENABLE_IF(detail::is_compiled_format<CompiledFormat>::value)>
609 FMT_INLINE std::basic_string<Char> format(const CompiledFormat& cf,
610                                           const Args&... args) {
611   basic_memory_buffer<Char> buffer;
612   cf.format(detail::buffer_appender<Char>(buffer), args...);
613   return to_string(buffer);
614 }
615 
616 template <typename OutputIt, typename CompiledFormat, typename... Args,
617           FMT_ENABLE_IF(detail::is_compiled_format<CompiledFormat>::value)>
618 OutputIt format_to(OutputIt out, const CompiledFormat& cf,
619                    const Args&... args) {
620   return cf.format(out, args...);
621 }
622 #  endif  // __cpp_if_constexpr
623 #endif    // FMT_USE_CONSTEXPR
624 
625 template <typename CompiledFormat, typename... Args,
626           typename Char = typename CompiledFormat::char_type,
627           FMT_ENABLE_IF(std::is_base_of<detail::basic_compiled_format,
628                                         CompiledFormat>::value)>
629 std::basic_string<Char> format(const CompiledFormat& cf, const Args&... args) {
630   basic_memory_buffer<Char> buffer;
631   using context = buffer_context<Char>;
632   detail::cf::vformat_to<context>(detail::buffer_appender<Char>(buffer), cf,
633                                   make_format_args<context>(args...));
634   return to_string(buffer);
635 }
636 
637 template <typename S, typename... Args,
638           FMT_ENABLE_IF(detail::is_compiled_string<S>::value)>
639 FMT_INLINE std::basic_string<typename S::char_type> format(const S&,
640                                                            Args&&... args) {
641 #ifdef __cpp_if_constexpr
642   if constexpr (std::is_same<typename S::char_type, char>::value) {
643     constexpr basic_string_view<typename S::char_type> str = S();
644     if (str.size() == 2 && str[0] == '{' && str[1] == '}')
645       return fmt::to_string(detail::first(args...));
646   }
647 #endif
648   constexpr auto compiled = detail::compile<Args...>(S());
649   return format(compiled, std::forward<Args>(args)...);
650 }
651 
652 template <typename OutputIt, typename CompiledFormat, typename... Args,
653           FMT_ENABLE_IF(std::is_base_of<detail::basic_compiled_format,
654                                         CompiledFormat>::value)>
655 OutputIt format_to(OutputIt out, const CompiledFormat& cf,
656                    const Args&... args) {
657   using char_type = typename CompiledFormat::char_type;
658   using context = format_context_t<OutputIt, char_type>;
659   return detail::cf::vformat_to<context>(out, cf,
660                                          make_format_args<context>(args...));
661 }
662 
663 template <typename OutputIt, typename S, typename... Args,
664           FMT_ENABLE_IF(detail::is_compiled_string<S>::value)>
665 OutputIt format_to(OutputIt out, const S&, const Args&... args) {
666   constexpr auto compiled = detail::compile<Args...>(S());
667   return format_to(out, compiled, args...);
668 }
669 
670 template <typename OutputIt, typename CompiledFormat, typename... Args>
671 auto format_to_n(OutputIt out, size_t n, const CompiledFormat& cf,
672                  const Args&... args) ->
673     typename std::enable_if<
674         detail::is_output_iterator<OutputIt,
675                                    typename CompiledFormat::char_type>::value &&
676             std::is_base_of<detail::basic_compiled_format,
677                             CompiledFormat>::value,
678         format_to_n_result<OutputIt>>::type {
679   auto it =
680       format_to(detail::truncating_iterator<OutputIt>(out, n), cf, args...);
681   return {it.base(), it.count()};
682 }
683 
684 template <typename OutputIt, typename S, typename... Args,
685           FMT_ENABLE_IF(detail::is_compiled_string<S>::value)>
686 format_to_n_result<OutputIt> format_to_n(OutputIt out, size_t n, const S&,
687                                          const Args&... args) {
688   constexpr auto compiled = detail::compile<Args...>(S());
689   auto it = format_to(detail::truncating_iterator<OutputIt>(out, n), compiled,
690                       args...);
691   return {it.base(), it.count()};
692 }
693 
694 template <typename CompiledFormat, typename... Args>
695 size_t formatted_size(const CompiledFormat& cf, const Args&... args) {
696   return format_to(detail::counting_iterator(), cf, args...).count();
697 }
698 
699 FMT_END_NAMESPACE
700 
701 #endif  // FMT_COMPILE_H_
702