1 /*
   2  * Copyright (c) 2014, Oracle and/or its affiliates. All rights reserved.
   3  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
   4  *
   5  * This code is free software; you can redistribute it and/or modify it
   6  * under the terms of the GNU General Public License version 2 only, as
   7  * published by the Free Software Foundation.
   8  *
   9  * This code is distributed in the hope that it will be useful, but WITHOUT
  10  * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
  11  * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
  12  * version 2 for more details (a copy is included in the LICENSE file that
  13  * accompanied this code).
  14  *
  15  * You should have received a copy of the GNU General Public License version
  16  * 2 along with this work; if not, write to the Free Software Foundation,
  17  * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
  18  *
  19  * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
  20  * or visit www.oracle.com if you need additional information or have any
  21  * questions.
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  23  */
  24 
  25 #ifndef SHARE_VM_UTILITIES_TRAITS_IS_CLASS_DEFINED_HPP
  26 #define SHARE_VM_UTILITIES_TRAITS_IS_CLASS_DEFINED_HPP
  27 
  28 #include "utilities/traits/enableIf.hpp"
  29 #include "utilities/traits/removeCv.hpp"
  30 #include "utilities/traits/isClassOrUnion.hpp"
  31 
  32 // Metafunction whose nested value member is true if T is defined
  33 // (complete), and false if T is incomplete.
  34 // If T is incomplete at the point where this
  35 // metafunction is invoked, it must never be defined elsewhere in the
  36 // program.
  37 // Returns false if T is not a class type.
  38 // Note: Currently can return true for a union, but this is subject to
  39 // change and should not be relied upon.
  40 template<typename T>
  41 class IsClassDefined {
  42   typedef char yes[1];
  43   typedef char no[2];
  44 
  45   template<typename U>
  46   static typename EnableIf<sizeof(U) != 0, yes>::type& check(U*);
  47   static no& check(...);
  48 
  49   typedef typename RemoveCv<T>::type TNoCv;
  50 
  51 public:
  52   static const bool value = IsClassOrUnion<TNoCv>::value &&
  53       sizeof(check((T*)0)) == sizeof(yes);
  54 };
  55 
  56 #endif // SHARE_VM_UTILITIES_TRAITS_IS_CLASS_DEFINED_HPP
  57