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85 lines
3.4 KiB
C++
85 lines
3.4 KiB
C++
// Copyright (C) 2015-2017 Free Software Foundation, Inc.
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//
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// This file is part of the GNU ISO C++ Library. This library is free
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// software; you can redistribute it and/or modify it under the
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// terms of the GNU General Public License as published by the
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// Free Software Foundation; either version 3, or (at your option)
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// any later version.
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// This library is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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// You should have received a copy of the GNU General Public License along
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// with this library; see the file COPYING3. If not see
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// <http://www.gnu.org/licenses/>.
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// { dg-do compile { target c++14 } }
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#include <experimental/type_traits>
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using std::declval;
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using std::ptrdiff_t;
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using std::experimental::is_detected;
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using std::experimental::is_detected_exact;
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using std::experimental::detected_or_t;
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using std::experimental::is_same_v;
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// Examples taken from N4502
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// archetypal helper alias for a copy assignment operation:
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template <class T>
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using copy_assign_t = decltype(declval<T&>() = declval<T const &>());
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// plausible implementation for the is_assignable type trait:
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template <class T>
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using is_copy_assignable = is_detected<copy_assign_t, T>;
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// plausible implementation for an augmented is_assignable type trait
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// that also checks the return type:
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template <class T>
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using is_canonical_copy_assignable = is_detected_exact<T&, copy_assign_t, T>;
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struct A { };
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struct B { B& operator=(const B&); };
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struct C { void operator=(const C&); };
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struct D { D& operator=(D&); };
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struct E { E& operator=(E&&); };
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static_assert( is_copy_assignable<A>::value, "A is copy assignable" );
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static_assert( is_copy_assignable<B>::value, "B is copy assignable" );
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static_assert( is_copy_assignable<C>::value, "C is copy assignable" );
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static_assert( !is_copy_assignable<D>::value, "D is not copy assignable" );
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static_assert( !is_copy_assignable<E>::value, "E is not copy assignable" );
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static_assert( is_canonical_copy_assignable<A>::value,
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"A has canonical copy assignment" );
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static_assert( is_canonical_copy_assignable<B>::value,
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"B has canonical copy assignment" );
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static_assert( !is_canonical_copy_assignable<C>::value,
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"C does not have canonical copy assignment" );
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static_assert( !is_canonical_copy_assignable<D>::value,
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"D does not have canonical copy assignment" );
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static_assert( !is_canonical_copy_assignable<E>::value,
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"E does not have canonical copy assignment" );
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// archetypal helper alias for a particular type member:
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template <class T>
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using diff_t = typename T::difference_type;
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// alias the type member, if it exists, otherwise alias ptrdiff_t:
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template <class Ptr>
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using difference_type = detected_or_t<ptrdiff_t, diff_t, Ptr>;
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struct has { using difference_type = char; };
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struct has_not { };
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struct inherits : has { };
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struct hides : private has { };
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struct reveals : private has { using has::difference_type; };
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static_assert( is_same_v<difference_type<has>, char>, "has" );
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static_assert( is_same_v<difference_type<has_not>, ptrdiff_t>, "has not" );
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static_assert( is_same_v<difference_type<inherits>, char>, "inherits" );
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static_assert( is_same_v<difference_type<hides>, ptrdiff_t>, "hides" );
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static_assert( is_same_v<difference_type<reveals>, char>, "reveals" );
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