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✏️ Editing: php_cxx_compile_stdcxx.m4 Read Only

dnl
dnl Based on https://www.gnu.org/software/autoconf-archive/ax_cxx_compile_stdcxx.html
dnl Author: Anatol Belski <ab@php.net>
dnl
dnl PHP_CXX_COMPILE_STDCXX(version, mandatory|optional, var_name_to_put_switch_in)
dnl
dnl ARGUMENTS
dnl
dnl first arg  - version as 11, 14 or 17
dnl second arg - if mandatory, the configure will fail when no features found.
dnl                   Optional will make configure silently continue
dnl third arg  - a variable name where the corresponding switch would be put. If
dnl              the variable is already defined, its contents will be overwritten.
dnl
dnl EXAMPLE
dnl
dnl  PHP_CXX_COMPILE_STDCXX(14, mandatory, MY_STDCXX_SWiTCH)
dnl  echo $MY_STDCXX_SWITCH
dnl

dnl
dnl PHP specific implementation start.
dnl

AC_DEFUN([PHP_CXX_COMPILE_STDCXX], [dnl
  m4_if([$1], [11], [ax_cxx_compile_alternatives="11 0x"],
        [$1], [14], [ax_cxx_compile_alternatives="14 1y"],
        [$1], [17], [ax_cxx_compile_alternatives="17 1z"],
        [m4_fatal([invalid first argument `$1' to PHP_CXX_COMPILE_STDCXX])])dnl
  m4_if([$2], [], [ax_cxx_compile_cxx$1_required=true],
        [$2], [mandatory], [ax_cxx_compile_cxx$1_required=true],
        [$2], [optional], [ax_cxx_compile_cxx$1_required=false],
        [m4_fatal([invalid third argument `$2' to PHP_CXX_COMPILE_STDCXX])])dnl
  AC_LANG_PUSH([C++])dnl
  ac_success=no

dnl HP's aCC needs +std=c++11 according to:
  dnl http://h21007.www2.hp.com/portal/download/files/unprot/aCxx/PDF_Release_Notes/769149-001.pdf
  dnl Cray's crayCC needs "-h std=c++11"
  for alternative in ${ax_cxx_compile_alternatives}; do
    for switch in -std=c++${alternative} +std=c++${alternative} "-h std=c++${alternative}"; do
      cachevar=AS_TR_SH([ax_cv_cxx_compile_cxx$1_$switch])
      AC_CACHE_CHECK(whether $CXX supports C++$1 features with $switch,
                     $cachevar,
          [ac_save_CXX="$CXX"
           CXX="$CXX $switch"
           AC_COMPILE_IFELSE([AC_LANG_SOURCE([_AX_CXX_COMPILE_STDCXX_testbody_$1])],
            [eval $cachevar=yes],
            [eval $cachevar=no])
           CXX="$ac_save_CXX"])
      if eval test x\$$cachevar = xyes; then
        eval AS_TR_SH([$3])="$switch"
        ac_success=yes
        break
      fi
    done
    if test x$ac_success = xyes; then
      break
    fi
  done

AC_LANG_POP([C++])
  if test x$ax_cxx_compile_cxx$1_required = xtrue; then
    if test x$ac_success = xno; then
      AC_MSG_ERROR([*** A compiler with support for C++$1 language features is required.])
    fi
  fi
  if test x$ac_success = xno; then
    AC_MSG_NOTICE([No compiler with C++$1 support was found])
  fi
  AC_SUBST(HAVE_CXX$1)
])

dnl
dnl PHP specific implementation end.
dnl The relevant part of the unchanged original implementation is below.
dnl

#
# LICENSE
#
#   Copyright (c) 2008 Benjamin Kosnik <bkoz@redhat.com>
#   Copyright (c) 2012 Zack Weinberg <zackw@panix.com>
#   Copyright (c) 2013 Roy Stogner <roystgnr@ices.utexas.edu>
#   Copyright (c) 2014, 2015 Google Inc.; contributed by Alexey Sokolov <sokolov@google.com>
#   Copyright (c) 2015 Paul Norman <penorman@mac.com>
#   Copyright (c) 2015 Moritz Klammler <moritz@klammler.eu>
#   Copyright (c) 2016, 2018 Krzesimir Nowak <qdlacz@gmail.com>
#   Copyright (c) 2019 Enji Cooper <yaneurabeya@gmail.com>
#
#   Copying and distribution of this file, with or without modification, are
#   permitted in any medium without royalty provided the copyright notice
#   and this notice are preserved.  This file is offered as-is, without any
#   warranty.

dnl  Test body for checking C++11 support

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_11],
  _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
)

dnl  Test body for checking C++14 support

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_14],
  _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
  _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
)

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_17],
  _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
  _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
  _AX_CXX_COMPILE_STDCXX_testbody_new_in_17
)

dnl  Tests for new features in C++11

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_11], [[

// If the compiler admits that it is not ready for C++11, why torture it?
// Hopefully, this will speed up the test.

#ifndef __cplusplus

#error "This is not a C++ compiler"

#elif __cplusplus < 201103L

#error "This is not a C++11 compiler"

#else

namespace cxx11
{

namespace test_static_assert
  {

template <typename T>
    struct check
    {
      static_assert(sizeof(int) <= sizeof(T), "not big enough");
    };

}

namespace test_final_override
  {

struct Base
    {
      virtual ~Base() {}
      virtual void f() {}
    };

struct Derived : public Base
    {
      virtual ~Derived() override {}
      virtual void f() override {}
    };

}

namespace test_double_right_angle_brackets
  {

template < typename T >
    struct check {};

typedef check<void> single_type;
    typedef check<check<void>> double_type;
    typedef check<check<check<void>>> triple_type;
    typedef check<check<check<check<void>>>> quadruple_type;

}

namespace test_decltype
  {

int
    f()
    {
      int a = 1;
      decltype(a) b = 2;
      return a + b;
    }

}

namespace test_type_deduction
  {

template < typename T1, typename T2 >
    struct is_same
    {
      static const bool value = false;
    };

template < typename T >
    struct is_same<T, T>
    {
      static const bool value = true;
    };

template < typename T1, typename T2 >
    auto
    add(T1 a1, T2 a2) -> decltype(a1 + a2)
    {
      return a1 + a2;
    }

int
    test(const int c, volatile int v)
    {
      static_assert(is_same<int, decltype(0)>::value == true, "");
      static_assert(is_same<int, decltype(c)>::value == false, "");
      static_assert(is_same<int, decltype(v)>::value == false, "");
      auto ac = c;
      auto av = v;
      auto sumi = ac + av + 'x';
      auto sumf = ac + av + 1.0;
      static_assert(is_same<int, decltype(ac)>::value == true, "");
      static_assert(is_same<int, decltype(av)>::value == true, "");
      static_assert(is_same<int, decltype(sumi)>::value == true, "");
      static_assert(is_same<int, decltype(sumf)>::value == false, "");
      static_assert(is_same<int, decltype(add(c, v))>::value == true, "");
      return (sumf > 0.0) ? sumi : add(c, v);
    }

}

namespace test_noexcept
  {

int f() { return 0; }
    int g() noexcept { return 0; }

static_assert(noexcept(f()) == false, "");
    static_assert(noexcept(g()) == true, "");

}

namespace test_constexpr
  {

template < typename CharT >
    unsigned long constexpr
    strlen_c_r(const CharT *const s, const unsigned long acc) noexcept
    {
      return *s ? strlen_c_r(s + 1, acc + 1) : acc;
    }

template < typename CharT >
    unsigned long constexpr
    strlen_c(const CharT *const s) noexcept
    {
      return strlen_c_r(s, 0UL);
    }

static_assert(strlen_c("") == 0UL, "");
    static_assert(strlen_c("1") == 1UL, "");
    static_assert(strlen_c("example") == 7UL, "");
    static_assert(strlen_c("another\0example") == 7UL, "");

}

namespace test_rvalue_references
  {

template < int N >
    struct answer
    {
      static constexpr int value = N;
    };

answer<1> f(int&)       { return answer<1>(); }
    answer<2> f(const int&) { return answer<2>(); }
    answer<3> f(int&&)      { return answer<3>(); }

void
    test()
    {
      int i = 0;
      const int c = 0;
      static_assert(decltype(f(i))::value == 1, "");
      static_assert(decltype(f(c))::value == 2, "");
      static_assert(decltype(f(0))::value == 3, "");
    }

}

namespace test_uniform_initialization
  {

struct test
    {
      static const int zero {};
      static const int one {1};
    };

static_assert(test::zero == 0, "");
    static_assert(test::one == 1, "");

}

namespace test_lambdas
  {

void
    test1()
    {
      auto lambda1 = [](){};
      auto lambda2 = lambda1;
      lambda1();
      lambda2();
    }

int
    test2()
    {
      auto a = [](int i, int j){ return i + j; }(1, 2);
      auto b = []() -> int { return '0'; }();
      auto c = [=](){ return a + b; }();
      auto d = [&](){ return c; }();
      auto e = [a, &b](int x) mutable {
        const auto identity = [](int y){ return y; };
        for (auto i = 0; i < a; ++i)
          a += b--;
        return x + identity(a + b);
      }(0);
      return a + b + c + d + e;
    }

int
    test3()
    {
      const auto nullary = [](){ return 0; };
      const auto unary = [](int x){ return x; };
      using nullary_t = decltype(nullary);
      using unary_t = decltype(unary);
      const auto higher1st = [](nullary_t f){ return f(); };
      const auto higher2nd = [unary](nullary_t f1){
        return [unary, f1](unary_t f2){ return f2(unary(f1())); };
      };
      return higher1st(nullary) + higher2nd(nullary)(unary);
    }

}

namespace test_variadic_templates
  {

template <int...>
    struct sum;

template <int N0, int... N1toN>
    struct sum<N0, N1toN...>
    {
      static constexpr auto value = N0 + sum<N1toN...>::value;
    };

template <>
    struct sum<>
    {
      static constexpr auto value = 0;
    };

static_assert(sum<>::value == 0, "");
    static_assert(sum<1>::value == 1, "");
    static_assert(sum<23>::value == 23, "");
    static_assert(sum<1, 2>::value == 3, "");
    static_assert(sum<5, 5, 11>::value == 21, "");
    static_assert(sum<2, 3, 5, 7, 11, 13>::value == 41, "");

}

// http://stackoverflow.com/questions/13728184/template-aliases-and-sfinae
  // Clang 3.1 fails with headers of libstd++ 4.8.3 when using std::function
  // because of this.
  namespace test_template_alias_sfinae
  {

struct foo {};

template<typename T>
    using member = typename T::member_type;

template<typename T>
    void func(...) {}

template<typename T>
    void func(member<T>*) {}

void test();

void test() { func<foo>(0); }

}

}  // namespace cxx11

#endif  // __cplusplus >= 201103L

]])

dnl  Tests for new features in C++14

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_14], [[

// If the compiler admits that it is not ready for C++14, why torture it?
// Hopefully, this will speed up the test.

#ifndef __cplusplus

#error "This is not a C++ compiler"

#elif __cplusplus < 201402L

#error "This is not a C++14 compiler"

#else

namespace cxx14
{

namespace test_polymorphic_lambdas
  {

int
    test()
    {
      const auto lambda = [](auto&&... args){
        const auto istiny = [](auto x){
          return (sizeof(x) == 1UL) ? 1 : 0;
        };
        const int aretiny[] = { istiny(args)... };
        return aretiny[0];
      };
      return lambda(1, 1L, 1.0f, '1');
    }

}

namespace test_binary_literals
  {

constexpr auto ivii = 0b0000000000101010;
    static_assert(ivii == 42, "wrong value");

}

namespace test_generalized_constexpr
  {

template < typename CharT >
    constexpr unsigned long
    strlen_c(const CharT *const s) noexcept
    {
      auto length = 0UL;
      for (auto p = s; *p; ++p)
        ++length;
      return length;
    }

static_assert(strlen_c("") == 0UL, "");
    static_assert(strlen_c("x") == 1UL, "");
    static_assert(strlen_c("test") == 4UL, "");
    static_assert(strlen_c("another\0test") == 7UL, "");

}

namespace test_lambda_init_capture
  {

int
    test()
    {
      auto x = 0;
      const auto lambda1 = [a = x](int b){ return a + b; };
      const auto lambda2 = [a = lambda1(x)](){ return a; };
      return lambda2();
    }

}

namespace test_digit_separators
  {

constexpr auto ten_million = 100'000'000;
    static_assert(ten_million == 100000000, "");

}

namespace test_return_type_deduction
  {

auto f(int& x) { return x; }
    decltype(auto) g(int& x) { return x; }

template < typename T1, typename T2 >
    struct is_same
    {
      static constexpr auto value = false;
    };

template < typename T >
    struct is_same<T, T>
    {
      static constexpr auto value = true;
    };

int
    test()
    {
      auto x = 0;
      static_assert(is_same<int, decltype(f(x))>::value, "");
      static_assert(is_same<int&, decltype(g(x))>::value, "");
      return x;
    }

}

}  // namespace cxx14

#endif  // __cplusplus >= 201402L

]])

dnl  Tests for new features in C++17

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_17], [[

// If the compiler admits that it is not ready for C++17, why torture it?
// Hopefully, this will speed up the test.

#ifndef __cplusplus

#error "This is not a C++ compiler"

#elif __cplusplus < 201703L

#error "This is not a C++17 compiler"

#else

#include <initializer_list>
#include <utility>
#include <type_traits>

namespace cxx17
{

namespace test_constexpr_lambdas
  {

constexpr int foo = [](){return 42;}();

}

namespace test::nested_namespace::definitions
  {

}

namespace test_fold_expression
  {

template<typename... Args>
    int multiply(Args... args)
    {
      return (args * ... * 1);
    }

template<typename... Args>
    bool all(Args... args)
    {
      return (args && ...);
    }

}

namespace test_extended_static_assert
  {

static_assert (true);

}

namespace test_auto_brace_init_list
  {

auto foo = {5};
    auto bar {5};

static_assert(std::is_same<std::initializer_list<int>, decltype(foo)>::value);
    static_assert(std::is_same<int, decltype(bar)>::value);
  }

namespace test_typename_in_template_template_parameter
  {

template<template<typename> typename X> struct D;

}

namespace test_fallthrough_nodiscard_maybe_unused_attributes
  {

int f1()
    {
      return 42;
    }

[[nodiscard]] int f2()
    {
      [[maybe_unused]] auto unused = f1();

switch (f1())
      {
      case 17:
        f1();
        [[fallthrough]];
      case 42:
        f1();
      }
      return f1();
    }

}

namespace test_extended_aggregate_initialization
  {

struct base1
    {
      int b1, b2 = 42;
    };

struct base2
    {
      base2() {
        b3 = 42;
      }
      int b3;
    };

struct derived : base1, base2
    {
        int d;
    };

derived d1 {{1, 2}, {}, 4};  // full initialization
    derived d2 {{}, {}, 4};      // value-initialized bases

}

namespace test_general_range_based_for_loop
  {

struct iter
    {
      int i;

int& operator* ()
      {
        return i;
      }

const int& operator* () const
      {
        return i;
      }

iter& operator++()
      {
        ++i;
        return *this;
      }
    };

struct sentinel
    {
      int i;
    };

bool operator== (const iter& i, const sentinel& s)
    {
      return i.i == s.i;
    }

bool operator!= (const iter& i, const sentinel& s)
    {
      return !(i == s);
    }

struct range
    {
      iter begin() const
      {
        return {0};
      }

sentinel end() const
      {
        return {5};
      }
    };

void f()
    {
      range r {};

for (auto i : r)
      {
        [[maybe_unused]] auto v = i;
      }
    }

}

namespace test_lambda_capture_asterisk_this_by_value
  {

struct t
    {
      int i;
      int foo()
      {
        return [*this]()
        {
          return i;
        }();
      }
    };

}

namespace test_enum_class_construction
  {

enum class byte : unsigned char
    {};

byte foo {42};

}

namespace test_constexpr_if
  {

template <bool cond>
    int f ()
    {
      if constexpr(cond)
      {
        return 13;
      }
      else
      {
        return 42;
      }
    }

}

namespace test_selection_statement_with_initializer
  {

int f()
    {
      return 13;
    }

int f2()
    {
      if (auto i = f(); i > 0)
      {
        return 3;
      }

switch (auto i = f(); i + 4)
      {
      case 17:
        return 2;

default:
        return 1;
      }
    }

}

namespace test_template_argument_deduction_for_class_templates
  {

template <typename T1, typename T2>
    struct pair
    {
      pair (T1 p1, T2 p2)
        : m1 {p1},
          m2 {p2}
      {}

T1 m1;
      T2 m2;
    };

void f()
    {
      [[maybe_unused]] auto p = pair{13, 42u};
    }

}

namespace test_non_type_auto_template_parameters
  {

template <auto n>
    struct B
    {};

B<5> b1;
    B<'a'> b2;

}

namespace test_structured_bindings
  {

int arr[2] = { 1, 2 };
    std::pair<int, int> pr = { 1, 2 };

auto f1() -> int(&)[2]
    {
      return arr;
    }

auto f2() -> std::pair<int, int>&
    {
      return pr;
    }

struct S
    {
      int x1 : 2;
      volatile double y1;
    };

S f3()
    {
      return {};
    }

auto [ x1, y1 ] = f1();
    auto& [ xr1, yr1 ] = f1();
    auto [ x2, y2 ] = f2();
    auto& [ xr2, yr2 ] = f2();
    const auto [ x3, y3 ] = f3();

}

namespace test_exception_spec_type_system
  {

struct Good {};
    struct Bad {};

void g1() noexcept;
    void g2();

template<typename T>
    Bad
    f(T*, T*);

template<typename T1, typename T2>
    Good
    f(T1*, T2*);

static_assert (std::is_same_v<Good, decltype(f(g1, g2))>);

}

namespace test_inline_variables
  {

template<class T> void f(T)
    {}

template<class T> inline T g(T)
    {
      return T{};
    }

template<> inline void f<>(int)
    {}

template<> int g<>(int)
    {
      return 5;
    }

}

}  // namespace cxx17

#endif  // __cplusplus < 201703L

]])

✏️ Editing: php_cxx_compile_stdcxx.m4 Read Only

dnl
dnl PHP specific implementation start.
dnl

dnl
dnl PHP specific implementation end.
dnl The relevant part of the unchanged original implementation is below.
dnl

dnl  Test body for checking C++11 support

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_11],
  _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
)

dnl  Test body for checking C++14 support

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_14],
  _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
  _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
)

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_17],
  _AX_CXX_COMPILE_STDCXX_testbody_new_in_11
  _AX_CXX_COMPILE_STDCXX_testbody_new_in_14
  _AX_CXX_COMPILE_STDCXX_testbody_new_in_17
)

dnl  Tests for new features in C++11

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_11], [[

// If the compiler admits that it is not ready for C++11, why torture it?
// Hopefully, this will speed up the test.

#ifndef __cplusplus

#error "This is not a C++ compiler"

#elif __cplusplus < 201103L

#error "This is not a C++11 compiler"

#else

namespace cxx11
{

namespace test_static_assert
  {

template <typename T>
    struct check
    {
      static_assert(sizeof(int) <= sizeof(T), "not big enough");
    };

}

namespace test_final_override
  {

struct Base
    {
      virtual ~Base() {}
      virtual void f() {}
    };

struct Derived : public Base
    {
      virtual ~Derived() override {}
      virtual void f() override {}
    };

}

namespace test_double_right_angle_brackets
  {

template < typename T >
    struct check {};

typedef check<void> single_type;
    typedef check<check<void>> double_type;
    typedef check<check<check<void>>> triple_type;
    typedef check<check<check<check<void>>>> quadruple_type;

}

namespace test_decltype
  {

int
    f()
    {
      int a = 1;
      decltype(a) b = 2;
      return a + b;
    }

}

namespace test_type_deduction
  {

template < typename T1, typename T2 >
    struct is_same
    {
      static const bool value = false;
    };

template < typename T >
    struct is_same<T, T>
    {
      static const bool value = true;
    };

template < typename T1, typename T2 >
    auto
    add(T1 a1, T2 a2) -> decltype(a1 + a2)
    {
      return a1 + a2;
    }

}

namespace test_noexcept
  {

int f() { return 0; }
    int g() noexcept { return 0; }

static_assert(noexcept(f()) == false, "");
    static_assert(noexcept(g()) == true, "");

}

namespace test_constexpr
  {

template < typename CharT >
    unsigned long constexpr
    strlen_c_r(const CharT *const s, const unsigned long acc) noexcept
    {
      return *s ? strlen_c_r(s + 1, acc + 1) : acc;
    }

template < typename CharT >
    unsigned long constexpr
    strlen_c(const CharT *const s) noexcept
    {
      return strlen_c_r(s, 0UL);
    }

static_assert(strlen_c("") == 0UL, "");
    static_assert(strlen_c("1") == 1UL, "");
    static_assert(strlen_c("example") == 7UL, "");
    static_assert(strlen_c("another\0example") == 7UL, "");

}

namespace test_rvalue_references
  {

template < int N >
    struct answer
    {
      static constexpr int value = N;
    };

answer<1> f(int&)       { return answer<1>(); }
    answer<2> f(const int&) { return answer<2>(); }
    answer<3> f(int&&)      { return answer<3>(); }

}

namespace test_uniform_initialization
  {

struct test
    {
      static const int zero {};
      static const int one {1};
    };

static_assert(test::zero == 0, "");
    static_assert(test::one == 1, "");

}

namespace test_lambdas
  {

void
    test1()
    {
      auto lambda1 = [](){};
      auto lambda2 = lambda1;
      lambda1();
      lambda2();
    }

}

namespace test_variadic_templates
  {

template <int...>
    struct sum;

template <int N0, int... N1toN>
    struct sum<N0, N1toN...>
    {
      static constexpr auto value = N0 + sum<N1toN...>::value;
    };

template <>
    struct sum<>
    {
      static constexpr auto value = 0;
    };

}

struct foo {};

template<typename T>
    using member = typename T::member_type;

template<typename T>
    void func(...) {}

template<typename T>
    void func(member<T>*) {}

void test();

void test() { func<foo>(0); }

}

}  // namespace cxx11

#endif  // __cplusplus >= 201103L

]])

dnl  Tests for new features in C++14

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_14], [[

// If the compiler admits that it is not ready for C++14, why torture it?
// Hopefully, this will speed up the test.

#ifndef __cplusplus

#error "This is not a C++ compiler"

#elif __cplusplus < 201402L

#error "This is not a C++14 compiler"

#else

namespace cxx14
{

namespace test_polymorphic_lambdas
  {

}

namespace test_binary_literals
  {

constexpr auto ivii = 0b0000000000101010;
    static_assert(ivii == 42, "wrong value");

}

namespace test_generalized_constexpr
  {

static_assert(strlen_c("") == 0UL, "");
    static_assert(strlen_c("x") == 1UL, "");
    static_assert(strlen_c("test") == 4UL, "");
    static_assert(strlen_c("another\0test") == 7UL, "");

}

namespace test_lambda_init_capture
  {

int
    test()
    {
      auto x = 0;
      const auto lambda1 = [a = x](int b){ return a + b; };
      const auto lambda2 = [a = lambda1(x)](){ return a; };
      return lambda2();
    }

}

namespace test_digit_separators
  {

constexpr auto ten_million = 100'000'000;
    static_assert(ten_million == 100000000, "");

}

namespace test_return_type_deduction
  {

auto f(int& x) { return x; }
    decltype(auto) g(int& x) { return x; }

template < typename T1, typename T2 >
    struct is_same
    {
      static constexpr auto value = false;
    };

template < typename T >
    struct is_same<T, T>
    {
      static constexpr auto value = true;
    };

int
    test()
    {
      auto x = 0;
      static_assert(is_same<int, decltype(f(x))>::value, "");
      static_assert(is_same<int&, decltype(g(x))>::value, "");
      return x;
    }

}

}  // namespace cxx14

#endif  // __cplusplus >= 201402L

]])

dnl  Tests for new features in C++17

m4_define([_AX_CXX_COMPILE_STDCXX_testbody_new_in_17], [[

// If the compiler admits that it is not ready for C++17, why torture it?
// Hopefully, this will speed up the test.

#ifndef __cplusplus

#error "This is not a C++ compiler"

#elif __cplusplus < 201703L

#error "This is not a C++17 compiler"

#else

#include <initializer_list>
#include <utility>
#include <type_traits>

namespace cxx17
{

namespace test_constexpr_lambdas
  {

constexpr int foo = [](){return 42;}();

}

namespace test::nested_namespace::definitions
  {

}

namespace test_fold_expression
  {

template<typename... Args>
    int multiply(Args... args)
    {
      return (args * ... * 1);
    }

template<typename... Args>
    bool all(Args... args)
    {
      return (args && ...);
    }

}

namespace test_extended_static_assert
  {

static_assert (true);

}

namespace test_auto_brace_init_list
  {

auto foo = {5};
    auto bar {5};

static_assert(std::is_same<std::initializer_list<int>, decltype(foo)>::value);
    static_assert(std::is_same<int, decltype(bar)>::value);
  }

namespace test_typename_in_template_template_parameter
  {

template<template<typename> typename X> struct D;

}

namespace test_fallthrough_nodiscard_maybe_unused_attributes
  {

int f1()
    {
      return 42;
    }

[[nodiscard]] int f2()
    {
      [[maybe_unused]] auto unused = f1();

switch (f1())
      {
      case 17:
        f1();
        [[fallthrough]];
      case 42:
        f1();
      }
      return f1();
    }

}

namespace test_extended_aggregate_initialization
  {

struct base1
    {
      int b1, b2 = 42;
    };

struct base2
    {
      base2() {
        b3 = 42;
      }
      int b3;
    };

struct derived : base1, base2
    {
        int d;
    };

derived d1 {{1, 2}, {}, 4};  // full initialization
    derived d2 {{}, {}, 4};      // value-initialized bases

}

namespace test_general_range_based_for_loop
  {

struct iter
    {
      int i;

int& operator* ()
      {
        return i;
      }

const int& operator* () const
      {
        return i;
      }

iter& operator++()
      {
        ++i;
        return *this;
      }
    };

struct sentinel
    {
      int i;
    };

bool operator== (const iter& i, const sentinel& s)
    {
      return i.i == s.i;
    }

bool operator!= (const iter& i, const sentinel& s)
    {
      return !(i == s);
    }

struct range
    {
      iter begin() const
      {
        return {0};
      }

sentinel end() const
      {
        return {5};
      }
    };

void f()
    {
      range r {};

for (auto i : r)
      {
        [[maybe_unused]] auto v = i;
      }
    }

}

namespace test_lambda_capture_asterisk_this_by_value
  {

struct t
    {
      int i;
      int foo()
      {
        return [*this]()
        {
          return i;
        }();
      }
    };

}

namespace test_enum_class_construction
  {

enum class byte : unsigned char
    {};

byte foo {42};

}

namespace test_constexpr_if
  {

template <bool cond>
    int f ()
    {
      if constexpr(cond)
      {
        return 13;
      }
      else
      {
        return 42;
      }
    }

}

namespace test_selection_statement_with_initializer
  {

int f()
    {
      return 13;
    }

int f2()
    {
      if (auto i = f(); i > 0)
      {
        return 3;
      }

switch (auto i = f(); i + 4)
      {
      case 17:
        return 2;

default:
        return 1;
      }
    }

}

namespace test_template_argument_deduction_for_class_templates
  {

template <typename T1, typename T2>
    struct pair
    {
      pair (T1 p1, T2 p2)
        : m1 {p1},
          m2 {p2}
      {}

T1 m1;
      T2 m2;
    };

void f()
    {
      [[maybe_unused]] auto p = pair{13, 42u};
    }

}

namespace test_non_type_auto_template_parameters
  {

template <auto n>
    struct B
    {};

B<5> b1;
    B<'a'> b2;

}

namespace test_structured_bindings
  {

int arr[2] = { 1, 2 };
    std::pair<int, int> pr = { 1, 2 };

auto f1() -> int(&)[2]
    {
      return arr;
    }

auto f2() -> std::pair<int, int>&
    {
      return pr;
    }

struct S
    {
      int x1 : 2;
      volatile double y1;
    };

S f3()
    {
      return {};
    }

auto [ x1, y1 ] = f1();
    auto& [ xr1, yr1 ] = f1();
    auto [ x2, y2 ] = f2();
    auto& [ xr2, yr2 ] = f2();
    const auto [ x3, y3 ] = f3();

}

namespace test_exception_spec_type_system
  {

struct Good {};
    struct Bad {};

void g1() noexcept;
    void g2();

template<typename T>
    Bad
    f(T*, T*);

template<typename T1, typename T2>
    Good
    f(T1*, T2*);

static_assert (std::is_same_v<Good, decltype(f(g1, g2))>);

}

namespace test_inline_variables
  {

template<class T> void f(T)
    {}

template<class T> inline T g(T)
    {
      return T{};
    }

template<> inline void f<>(int)
    {}

template<> int g<>(int)
    {
      return 5;
    }

}

}  // namespace cxx17

#endif  // __cplusplus < 201703L

]])

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