1 /*
   2  * Copyright (c) 2017, 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
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  23  */
  24 
  25 #ifndef SHARE_VM_METAPROGRAMMING_ISDERIVED_HPP
  26 #define SHARE_VM_METAPROGRAMMING_ISDERIVED_HPP
  27 
  28 #include "memory/allocation.hpp"
  29 #include "metaprogramming/integralConstant.hpp"
  30 #include "metaprogramming/isSame.hpp"
  31 
  32 // The IsDerived metafunction checks if a DerivedType is derived from a BaseType
  33 // or not. This will return false when used on a forward declared class.
  34 // Note that due to the ODR rule of C++, this metafunction must be used with care
  35 // in contexts where the DerivedType is guaranteed to be fully known.
  36 
  37 template <typename DerivedType, typename BaseType>
  38 struct IsDerivedHelper: public StackObj {
  39   operator BaseType* () const;
  40   operator DerivedType* ();
  41 };
  42 
  43 template <typename DerivedType, typename BaseType>
  44 struct IsDerivedImpl: public AllStatic {
  45   typedef char yes[1];
  46   typedef char no[2];
  47 
  48   template <typename T>
  49   static yes& test(DerivedType*, T);
  50   static no& test(BaseType*, int);
  51 
  52   static const bool value = IsSame<DerivedType, BaseType>::value ||
  53     sizeof(test(IsDerivedHelper<DerivedType, BaseType>(), 0)) == sizeof(yes);
  54 };
  55 
  56 template <typename DerivedType, typename BaseType>
  57 struct IsDerived: public IntegralConstant<bool, IsDerivedImpl<DerivedType, BaseType>::value> {};
  58 
  59 #endif // SHARE_VM_METAPROGRAMMING_ISDERIVED_HPP