libstdc++-v3/testsuite/std/concepts/concepts.lang/concept.defaultinitializable/lwg3149.cc

   1 // Copyright (C) 2019-2022 Free Software Foundation, Inc.
   2 //
   3 // This file is part of the GNU ISO C++ Library.  This library is free
   4 // software; you can redistribute it and/or modify it under the
   5 // terms of the GNU General Public License as published by the
   6 // Free Software Foundation; either version 3, or (at your option)
   7 // any later version.
   8
   9 // This library is distributed in the hope that it will be useful,
  10 // but WITHOUT ANY WARRANTY; without even the implied warranty of
  11 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  12 // GNU General Public License for more details.
  13
  14 // You should have received a copy of the GNU General Public License along
  15 // with this library; see the file COPYING3.  If not see
  16 // <http://www.gnu.org/licenses/>.
  17
  18 // { dg-options "-std=gnu++2a" }
  19 // { dg-do compile { target c++2a } }
  20
  21 #include <concepts>
  22
  23 // Default-initialization of const T is only valid for class types that are
  24 // const-default-constructible.
  25 static_assert( !std::default_initializable<const int> );
  26 static_assert( !std::default_initializable<const int[1]> );
  27 struct A { int i; };
  28 static_assert( !std::default_initializable<const A> );
  29 static_assert( !std::default_initializable<const A[1]> );
  30 struct B { int i; long l; };
  31 static_assert( !std::default_initializable<const B> );
  32 static_assert( !std::default_initializable<const B[1]> );
  33 struct C : A { };
  34 static_assert( !std::default_initializable<const C> );
  35 static_assert( !std::default_initializable<const C[1]> );
  36 struct D { A a; };
  37 static_assert( !std::default_initializable<const D> );
  38 static_assert( !std::default_initializable<const D[1]> );
  39
  40 struct S0 { explicit S0() = default; };
  41 struct S1 { S0 x; }; // Note: aggregate
  42 // S1{} would be ill-formed, due to copy-list-initialization of S1::x from {}
  43 static_assert( !std::default_initializable<S1> );