1# ===========================================================================
2#  https://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx.html
3# ===========================================================================
4#
5# SYNOPSIS
6#
7#   AX_CXX_COMPILE_STDCXX(VERSION, [ext|noext], [mandatory|optional])
8#
9# DESCRIPTION
10#
11#   Check for baseline language coverage in the compiler for the specified
12#   version of the C++ standard.  If necessary, add switches to CXX and
13#   CXXCPP to enable support.  VERSION may be '11' (for the C++11 standard)
14#   or '14' (for the C++14 standard).
15#
16#   The second argument, if specified, indicates whether you insist on an
17#   extended mode (e.g. -std=gnu++11) or a strict conformance mode (e.g.
18#   -std=c++11).  If neither is specified, you get whatever works, with
19#   preference for an extended mode.
20#
21#   The third argument, if specified 'mandatory' or if left unspecified,
22#   indicates that baseline support for the specified C++ standard is
23#   required and that the macro should error out if no mode with that
24#   support is found.  If specified 'optional', then configuration proceeds
25#   regardless, after defining HAVE_CXX${VERSION} if and only if a
26#   supporting mode is found.
27#
28# LICENSE
29#
30#   Copyright (c) 2008 Benjamin Kosnik <bkoz@redhat.com>
31#   Copyright (c) 2012 Zack Weinberg <zackw@panix.com>
32#   Copyright (c) 2013 Roy Stogner <roystgnr@ices.utexas.edu>
33#   Copyright (c) 2014, 2015 Google Inc.; contributed by Alexey Sokolov <sokolov@google.com>
34#   Copyright (c) 2015 Paul Norman <penorman@mac.com>
35#   Copyright (c) 2015 Moritz Klammler <moritz@klammler.eu>
36#   Copyright (c) 2016 Krzesimir Nowak <qdlacz@gmail.com>
37#
38#   Copying and distribution of this file, with or without modification, are
39#   permitted in any medium without royalty provided the copyright notice
40#   and this notice are preserved.  This file is offered as-is, without any
41#   warranty.
42
43#serial 7
44
45dnl  This macro is based on the code from the AX_CXX_COMPILE_STDCXX_11 macro
46dnl  (serial version number 13).
47
48AX_REQUIRE_DEFINED([AC_MSG_WARN])
49AC_DEFUN([AX_CXX_COMPILE_STDCXX], [dnl
50  m4_if([$1], [11], [ax_cxx_compile_alternatives="11 0x"],
51        [$1], [14], [ax_cxx_compile_alternatives="14 1y"],
52        [$1], [17], [ax_cxx_compile_alternatives="17 1z"],
53        [m4_fatal([invalid first argument `$1' to AX_CXX_COMPILE_STDCXX])])dnl
54  m4_if([$2], [], [],
55        [$2], [ext], [],
56        [$2], [noext], [],
57        [m4_fatal([invalid second argument `$2' to AX_CXX_COMPILE_STDCXX])])dnl
58  m4_if([$3], [], [ax_cxx_compile_cxx$1_required=true],
59        [$3], [mandatory], [ax_cxx_compile_cxx$1_required=true],
60        [$3], [optional], [ax_cxx_compile_cxx$1_required=false],
61        [m4_fatal([invalid third argument `$3' to AX_CXX_COMPILE_STDCXX])])
62  AC_LANG_PUSH([C++])dnl
63  ac_success=no
64  AC_CACHE_CHECK(whether $CXX supports C++$1 features by default,
65  ax_cv_cxx_compile_cxx$1,
66  [AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
67    [ax_cv_cxx_compile_cxx$1=yes],
68    [ax_cv_cxx_compile_cxx$1=no])])
69  if test x$ax_cv_cxx_compile_cxx$1 = xyes; then
70    ac_success=yes
71  fi
72
73  m4_if([$2], [noext], [], [dnl
74  if test x$ac_success = xno; then
75    for alternative in ${ax_cxx_compile_alternatives}; do
76      switch="-std=gnu++${alternative}"
77      cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
78      AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
79                     $cachevar,
80        [ac_save_CXX="$CXX"
81         CXX="$CXX $switch"
82         AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
83          [eval $cachevar=yes],
84          [eval $cachevar=no])
85         CXX="$ac_save_CXX"])
86      if eval test x\$$cachevar = xyes; then
87        CXX="$CXX $switch"
88        if test -n "$CXXCPP" ; then
89          CXXCPP="$CXXCPP $switch"
90        fi
91        ac_success=yes
92        break
93      fi
94    done
95  fi])
96
97  m4_if([$2], [ext], [], [dnl
98  if test x$ac_success = xno; then
99    dnl HP's aCC needs +std=c++11 according to:
100    dnl http://h21007.www2.hp.com/portal/download/files/unprot/aCxx/PDF_Release_Notes/769149-001.pdf
101    dnl Cray's crayCC needs "-h std=c++11"
102    for alternative in ${ax_cxx_compile_alternatives}; do
103      for switch in -std=c++${alternative} +std=c++${alternative} "-h std=c++${alternative}"; do
104        cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
105        AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
106                       $cachevar,
107          [ac_save_CXX="$CXX"
108           CXX="$CXX $switch"
109           AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
110            [eval $cachevar=yes],
111            [eval $cachevar=no])
112           CXX="$ac_save_CXX"])
113        if eval test x\$$cachevar = xyes; then
114          CXX="$CXX $switch"
115          if test -n "$CXXCPP" ; then
116            CXXCPP="$CXXCPP $switch"
117          fi
118          ac_success=yes
119          break
120        fi
121      done
122      if test x$ac_success = xyes; then
123        break
124      fi
125    done
126  fi])
127  AC_LANG_POP([C++])
128  if test x$ax_cxx_compile_cxx$1_required = xtrue; then
129    if test x$ac_success = xno; then
130      AC_MSG_ERROR([*** A compiler with support for C++$1 language features is required.])
131    fi
132  fi
133  if test x$ac_success = xno; then
134    HAVE_CXX$1=0
135    AC_MSG_NOTICE([No compiler with C++$1 support was found])
136  else
137    HAVE_CXX$1=1
138    AC_DEFINE(HAVE_CXX$1,1,
139              [define if the compiler supports basic C++$1 syntax])
140  fi
141  AC_SUBST(HAVE_CXX$1)
142  m4_if([$1], [17], [AC_MSG_WARN([C++17 is not yet standardized, so the checks may change in incompatible ways anytime])])
143])
144
145
146dnl  Test body for checking C++11 support
147
148m4_define([_AX_CXX_COMPILE_STDCXX_testbody_11],
149  _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
150)
151
152
153dnl  Test body for checking C++14 support
154
155m4_define([_AX_CXX_COMPILE_STDCXX_testbody_14],
156  _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
157  _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
158)
159
160m4_define([_AX_CXX_COMPILE_STDCXX_testbody_17],
161  _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
162  _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
163  _AX_CXX_COMPILE_STDCXX_testbody_new_in_17
164)
165
166dnl  Tests for new features in C++11
167
168m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_11], [[
169
170// If the compiler admits that it is not ready for C++11, why torture it?
171// Hopefully, this will speed up the test.
172
173#ifndef __cplusplus
174
175#error "This is not a C++ compiler"
176
177#elif __cplusplus < 201103L
178
179#error "This is not a C++11 compiler"
180
181#else
182
183namespace cxx11
184{
185
186  namespace test_static_assert
187  {
188
189    template <typename T>
190    struct check
191    {
192      static_assert(sizeof(int) <= sizeof(T), "not big enough");
193    };
194
195  }
196
197  namespace test_final_override
198  {
199
200    struct Base
201    {
202      virtual void f() {}
203    };
204
205    struct Derived : public Base
206    {
207      virtual void f() override {}
208    };
209
210  }
211
212  namespace test_double_right_angle_brackets
213  {
214
215    template < typename T >
216    struct check {};
217
218    typedef check<void> single_type;
219    typedef check<check<void>> double_type;
220    typedef check<check<check<void>>> triple_type;
221    typedef check<check<check<check<void>>>> quadruple_type;
222
223  }
224
225  namespace test_decltype
226  {
227
228    int
229    f()
230    {
231      int a = 1;
232      decltype(a) b = 2;
233      return a + b;
234    }
235
236  }
237
238  namespace test_type_deduction
239  {
240
241    template < typename T1, typename T2 >
242    struct is_same
243    {
244      static const bool value = false;
245    };
246
247    template < typename T >
248    struct is_same<T, T>
249    {
250      static const bool value = true;
251    };
252
253    template < typename T1, typename T2 >
254    auto
255    add(T1 a1, T2 a2) -> decltype(a1 + a2)
256    {
257      return a1 + a2;
258    }
259
260    int
261    test(const int c, volatile int v)
262    {
263      static_assert(is_same<int, decltype(0)>::value == true, "");
264      static_assert(is_same<int, decltype(c)>::value == false, "");
265      static_assert(is_same<int, decltype(v)>::value == false, "");
266      auto ac = c;
267      auto av = v;
268      auto sumi = ac + av + 'x';
269      auto sumf = ac + av + 1.0;
270      static_assert(is_same<int, decltype(ac)>::value == true, "");
271      static_assert(is_same<int, decltype(av)>::value == true, "");
272      static_assert(is_same<int, decltype(sumi)>::value == true, "");
273      static_assert(is_same<int, decltype(sumf)>::value == false, "");
274      static_assert(is_same<int, decltype(add(c, v))>::value == true, "");
275      return (sumf > 0.0) ? sumi : add(c, v);
276    }
277
278  }
279
280  namespace test_noexcept
281  {
282
283    int f() { return 0; }
284    int g() noexcept { return 0; }
285
286    static_assert(noexcept(f()) == false, "");
287    static_assert(noexcept(g()) == true, "");
288
289  }
290
291  namespace test_constexpr
292  {
293
294    template < typename CharT >
295    unsigned long constexpr
296    strlen_c_r(const CharT *const s, const unsigned long acc) noexcept
297    {
298      return *s ? strlen_c_r(s + 1, acc + 1) : acc;
299    }
300
301    template < typename CharT >
302    unsigned long constexpr
303    strlen_c(const CharT *const s) noexcept
304    {
305      return strlen_c_r(s, 0UL);
306    }
307
308    static_assert(strlen_c("") == 0UL, "");
309    static_assert(strlen_c("1") == 1UL, "");
310    static_assert(strlen_c("example") == 7UL, "");
311    static_assert(strlen_c("another\0example") == 7UL, "");
312
313  }
314
315  namespace test_rvalue_references
316  {
317
318    template < int N >
319    struct answer
320    {
321      static constexpr int value = N;
322    };
323
324    answer<1> f(int&)       { return answer<1>(); }
325    answer<2> f(const int&) { return answer<2>(); }
326    answer<3> f(int&&)      { return answer<3>(); }
327
328    void
329    test()
330    {
331      int i = 0;
332      const int c = 0;
333      static_assert(decltype(f(i))::value == 1, "");
334      static_assert(decltype(f(c))::value == 2, "");
335      static_assert(decltype(f(0))::value == 3, "");
336    }
337
338  }
339
340  namespace test_uniform_initialization
341  {
342
343    struct test
344    {
345      static const int zero {};
346      static const int one {1};
347    };
348
349    static_assert(test::zero == 0, "");
350    static_assert(test::one == 1, "");
351
352  }
353
354  namespace test_lambdas
355  {
356
357    void
358    test1()
359    {
360      auto lambda1 = [](){};
361      auto lambda2 = lambda1;
362      lambda1();
363      lambda2();
364    }
365
366    int
367    test2()
368    {
369      auto a = [](int i, int j){ return i + j; }(1, 2);
370      auto b = []() -> int { return '0'; }();
371      auto c = [=](){ return a + b; }();
372      auto d = [&](){ return c; }();
373      auto e = [a, &b](int x) mutable {
374        const auto identity = [](int y){ return y; };
375        for (auto i = 0; i < a; ++i)
376          a += b--;
377        return x + identity(a + b);
378      }(0);
379      return a + b + c + d + e;
380    }
381
382    int
383    test3()
384    {
385      const auto nullary = [](){ return 0; };
386      const auto unary = [](int x){ return x; };
387      using nullary_t = decltype(nullary);
388      using unary_t = decltype(unary);
389      const auto higher1st = [](nullary_t f){ return f(); };
390      const auto higher2nd = [unary](nullary_t f1){
391        return [unary, f1](unary_t f2){ return f2(unary(f1())); };
392      };
393      return higher1st(nullary) + higher2nd(nullary)(unary);
394    }
395
396  }
397
398  namespace test_variadic_templates
399  {
400
401    template <int...>
402    struct sum;
403
404    template <int N0, int... N1toN>
405    struct sum<N0, N1toN...>
406    {
407      static constexpr auto value = N0 + sum<N1toN...>::value;
408    };
409
410    template <>
411    struct sum<>
412    {
413      static constexpr auto value = 0;
414    };
415
416    static_assert(sum<>::value == 0, "");
417    static_assert(sum<1>::value == 1, "");
418    static_assert(sum<23>::value == 23, "");
419    static_assert(sum<1, 2>::value == 3, "");
420    static_assert(sum<5, 5, 11>::value == 21, "");
421    static_assert(sum<2, 3, 5, 7, 11, 13>::value == 41, "");
422
423  }
424
425  // http://stackoverflow.com/questions/13728184/template-aliases-and-sfinae
426  // Clang 3.1 fails with headers of libstd++ 4.8.3 when using std::function
427  // because of this.
428  namespace test_template_alias_sfinae
429  {
430
431    struct foo {};
432
433    template<typename T>
434    using member = typename T::member_type;
435
436    template<typename T>
437    void func(...) {}
438
439    template<typename T>
440    void func(member<T>*) {}
441
442    void test();
443
444    void test() { func<foo>(0); }
445
446  }
447
448}  // namespace cxx11
449
450#endif  // __cplusplus >= 201103L
451
452]])
453
454
455dnl  Tests for new features in C++14
456
457m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_14], [[
458
459// If the compiler admits that it is not ready for C++14, why torture it?
460// Hopefully, this will speed up the test.
461
462#ifndef __cplusplus
463
464#error "This is not a C++ compiler"
465
466#elif __cplusplus < 201402L
467
468#error "This is not a C++14 compiler"
469
470#else
471
472namespace cxx14
473{
474
475  namespace test_polymorphic_lambdas
476  {
477
478    int
479    test()
480    {
481      const auto lambda = [](auto&&... args){
482        const auto istiny = [](auto x){
483          return (sizeof(x) == 1UL) ? 1 : 0;
484        };
485        const int aretiny[] = { istiny(args)... };
486        return aretiny[0];
487      };
488      return lambda(1, 1L, 1.0f, '1');
489    }
490
491  }
492
493  namespace test_binary_literals
494  {
495
496    constexpr auto ivii = 0b0000000000101010;
497    static_assert(ivii == 42, "wrong value");
498
499  }
500
501  namespace test_generalized_constexpr
502  {
503
504    template < typename CharT >
505    constexpr unsigned long
506    strlen_c(const CharT *const s) noexcept
507    {
508      auto length = 0UL;
509      for (auto p = s; *p; ++p)
510        ++length;
511      return length;
512    }
513
514    static_assert(strlen_c("") == 0UL, "");
515    static_assert(strlen_c("x") == 1UL, "");
516    static_assert(strlen_c("test") == 4UL, "");
517    static_assert(strlen_c("another\0test") == 7UL, "");
518
519  }
520
521  namespace test_lambda_init_capture
522  {
523
524    int
525    test()
526    {
527      auto x = 0;
528      const auto lambda1 = [a = x](int b){ return a + b; };
529      const auto lambda2 = [a = lambda1(x)](){ return a; };
530      return lambda2();
531    }
532
533  }
534
535  namespace test_digit_separators
536  {
537
538    constexpr auto ten_million = 100'000'000;
539    static_assert(ten_million == 100000000, "");
540
541  }
542
543  namespace test_return_type_deduction
544  {
545
546    auto f(int& x) { return x; }
547    decltype(auto) g(int& x) { return x; }
548
549    template < typename T1, typename T2 >
550    struct is_same
551    {
552      static constexpr auto value = false;
553    };
554
555    template < typename T >
556    struct is_same<T, T>
557    {
558      static constexpr auto value = true;
559    };
560
561    int
562    test()
563    {
564      auto x = 0;
565      static_assert(is_same<int, decltype(f(x))>::value, "");
566      static_assert(is_same<int&, decltype(g(x))>::value, "");
567      return x;
568    }
569
570  }
571
572}  // namespace cxx14
573
574#endif  // __cplusplus >= 201402L
575
576]])
577
578
579dnl  Tests for new features in C++17
580
581m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_17], [[
582
583// If the compiler admits that it is not ready for C++17, why torture it?
584// Hopefully, this will speed up the test.
585
586#ifndef __cplusplus
587
588#error "This is not a C++ compiler"
589
590#elif __cplusplus <= 201402L
591
592#error "This is not a C++17 compiler"
593
594#else
595
596#if defined(__clang__)
597  #define REALLY_CLANG
598#else
599  #if defined(__GNUC__)
600    #define REALLY_GCC
601  #endif
602#endif
603
604#include <initializer_list>
605#include <utility>
606#include <type_traits>
607
608namespace cxx17
609{
610
611#if !defined(REALLY_CLANG)
612  namespace test_constexpr_lambdas
613  {
614
615    // TODO: test it with clang++ from git
616
617    constexpr int foo = [](){return 42;}();
618
619  }
620#endif // !defined(REALLY_CLANG)
621
622  namespace test::nested_namespace::definitions
623  {
624
625  }
626
627  namespace test_fold_expression
628  {
629
630    template<typename... Args>
631    int multiply(Args... args)
632    {
633      return (args * ... * 1);
634    }
635
636    template<typename... Args>
637    bool all(Args... args)
638    {
639      return (args && ...);
640    }
641
642  }
643
644  namespace test_extended_static_assert
645  {
646
647    static_assert (true);
648
649  }
650
651  namespace test_auto_brace_init_list
652  {
653
654    auto foo = {5};
655    auto bar {5};
656
657    static_assert(std::is_same<std::initializer_list<int>, decltype(foo)>::value);
658    static_assert(std::is_same<int, decltype(bar)>::value);
659  }
660
661  namespace test_typename_in_template_template_parameter
662  {
663
664    template<template<typename> typename X> struct D;
665
666  }
667
668  namespace test_fallthrough_nodiscard_maybe_unused_attributes
669  {
670
671    int f1()
672    {
673      return 42;
674    }
675
676    [[nodiscard]] int f2()
677    {
678      [[maybe_unused]] auto unused = f1();
679
680      switch (f1())
681      {
682      case 17:
683        f1();
684        [[fallthrough]];
685      case 42:
686        f1();
687      }
688      return f1();
689    }
690
691  }
692
693  namespace test_extended_aggregate_initialization
694  {
695
696    struct base1
697    {
698      int b1, b2 = 42;
699    };
700
701    struct base2
702    {
703      base2() {
704        b3 = 42;
705      }
706      int b3;
707    };
708
709    struct derived : base1, base2
710    {
711        int d;
712    };
713
714    derived d1 {{1, 2}, {}, 4};  // full initialization
715    derived d2 {{}, {}, 4};      // value-initialized bases
716
717  }
718
719  namespace test_general_range_based_for_loop
720  {
721
722    struct iter
723    {
724      int i;
725
726      int& operator* ()
727      {
728        return i;
729      }
730
731      const int& operator* () const
732      {
733        return i;
734      }
735
736      iter& operator++()
737      {
738        ++i;
739        return *this;
740      }
741    };
742
743    struct sentinel
744    {
745      int i;
746    };
747
748    bool operator== (const iter& i, const sentinel& s)
749    {
750      return i.i == s.i;
751    }
752
753    bool operator!= (const iter& i, const sentinel& s)
754    {
755      return !(i == s);
756    }
757
758    struct range
759    {
760      iter begin() const
761      {
762        return {0};
763      }
764
765      sentinel end() const
766      {
767        return {5};
768      }
769    };
770
771    void f()
772    {
773      range r {};
774
775      for (auto i : r)
776      {
777        [[maybe_unused]] auto v = i;
778      }
779    }
780
781  }
782
783  namespace test_lambda_capture_asterisk_this_by_value
784  {
785
786    struct t
787    {
788      int i;
789      int foo()
790      {
791        return [*this]()
792        {
793          return i;
794        }();
795      }
796    };
797
798  }
799
800  namespace test_enum_class_construction
801  {
802
803    enum class byte : unsigned char
804    {};
805
806    byte foo {42};
807
808  }
809
810  namespace test_constexpr_if
811  {
812
813    template <bool cond>
814    int f ()
815    {
816      if constexpr(cond)
817      {
818        return 13;
819      }
820      else
821      {
822        return 42;
823      }
824    }
825
826  }
827
828  namespace test_selection_statement_with_initializer
829  {
830
831    int f()
832    {
833      return 13;
834    }
835
836    int f2()
837    {
838      if (auto i = f(); i > 0)
839      {
840        return 3;
841      }
842
843      switch (auto i = f(); i + 4)
844      {
845      case 17:
846        return 2;
847
848      default:
849        return 1;
850      }
851    }
852
853  }
854
855#if !defined(REALLY_CLANG)
856  namespace test_template_argument_deduction_for_class_templates
857  {
858
859    // TODO: test it with clang++ from git
860
861    template <typename T1, typename T2>
862    struct pair
863    {
864      pair (T1 p1, T2 p2)
865        : m1 {p1},
866          m2 {p2}
867      {}
868
869      T1 m1;
870      T2 m2;
871    };
872
873    void f()
874    {
875      [[maybe_unused]] auto p = pair{13, 42u};
876    }
877
878  }
879#endif // !defined(REALLY_CLANG)
880
881  namespace test_non_type_auto_template_parameters
882  {
883
884    template <auto n>
885    struct B
886    {};
887
888    B<5> b1;
889    B<'a'> b2;
890
891  }
892
893#if !defined(REALLY_CLANG)
894  namespace test_structured_bindings
895  {
896
897    // TODO: test it with clang++ from git
898
899    int arr[2] = { 1, 2 };
900    std::pair<int, int> pr = { 1, 2 };
901
902    auto f1() -> int(&)[2]
903    {
904      return arr;
905    }
906
907    auto f2() -> std::pair<int, int>&
908    {
909      return pr;
910    }
911
912    struct S
913    {
914      int x1 : 2;
915      volatile double y1;
916    };
917
918    S f3()
919    {
920      return {};
921    }
922
923    auto [ x1, y1 ] = f1();
924    auto& [ xr1, yr1 ] = f1();
925    auto [ x2, y2 ] = f2();
926    auto& [ xr2, yr2 ] = f2();
927    const auto [ x3, y3 ] = f3();
928
929  }
930#endif // !defined(REALLY_CLANG)
931
932#if !defined(REALLY_CLANG)
933  namespace test_exception_spec_type_system
934  {
935
936    // TODO: test it with clang++ from git
937
938    struct Good {};
939    struct Bad {};
940
941    void g1() noexcept;
942    void g2();
943
944    template<typename T>
945    Bad
946    f(T*, T*);
947
948    template<typename T1, typename T2>
949    Good
950    f(T1*, T2*);
951
952    static_assert (std::is_same_v<Good, decltype(f(g1, g2))>);
953
954  }
955#endif // !defined(REALLY_CLANG)
956
957  namespace test_inline_variables
958  {
959
960    template<class T> void f(T)
961    {}
962
963    template<class T> inline T g(T)
964    {
965      return T{};
966    }
967
968    template<> inline void f<>(int)
969    {}
970
971    template<> int g<>(int)
972    {
973      return 5;
974    }
975
976  }
977
978}  // namespace cxx17
979
980#endif  // __cplusplus <= 201402L
981
982]])
983