ceph/src/boost/libs/optional/test/optional_test_constructible_from_other.cpp

   1 // Copyright (c) 2018 Andrey Semashev
   2 //
   3 // Use, modification, and distribution is subject to the Boost Software
   4 // License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
   5 // http://www.boost.org/LICENSE_1_0.txt)
   6
   7 // The test verifies that Boost.Optional copy constructors do not attempt to invoke
   8 // the element type initializing constructors from templated arguments
   9
  10 #include <boost/optional/optional.hpp>
  11 #include <boost/core/enable_if.hpp>
  12
  13 struct no_type
  14 {
  15     char data;
  16 };
  17
  18 struct yes_type
  19 {
  20     char data[2];
  21 };
  22
  23 template< unsigned int Size >
  24 struct size_tag {};
  25
  26 template< typename T, typename U >
  27 struct is_constructible
  28 {
  29     template< typename T1, typename U1 >
  30     static yes_type check_helper(size_tag< sizeof(static_cast< T1 >(U1())) >*);
  31     template< typename T1, typename U1 >
  32     static no_type check_helper(...);
  33
  34     static const bool value = sizeof(check_helper< T, U >(0)) == sizeof(yes_type);
  35 };
  36
  37 template< typename T >
  38 class wrapper
  39 {
  40 public:
  41     wrapper() {}
  42     wrapper(wrapper const&) {}
  43     template< typename U >
  44     wrapper(U const&, typename boost::enable_if_c< is_constructible< T, U >::value, int >::type = 0) {}
  45 };
  46
  47 inline boost::optional< wrapper< int > > foo()
  48 {
  49     return boost::optional< wrapper< int > >();
  50 }
  51
  52 int main()
  53 {
  54     // Invokes boost::optional copy constructor. Should not invoke wrapper constructor from U.
  55     boost::optional< wrapper< int > > res = foo();
  56     return 0;
  57 }