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

    21  * questions.

    22  *

    23  */

    24 

    25 #ifndef SHARE_VM_METAPROGRAMMING_ENABLEIF_HPP

    26 #define SHARE_VM_METAPROGRAMMING_ENABLEIF_HPP

    27 

    28 #include "memory/allocation.hpp"

    29 

    30 // This metaprogramming tool allows explicitly enabling and disabling overloads

    31 // of member functions depending on whether the condition B holds true.

    32 // For example typename EnableIf<IsPointer<T>::value>::type func(T ptr) would

    33 // only become an overload the compiler chooses from if the type T is a pointer.

    34 // If it is not, then the template definition is not expanded and there will be

    35 // no compiler error if there is another overload of func that is selected when

    36 // T is not a pointer. Like for example

    37 // typename EnableIf<!IsPointer<T>::value>::type func(T not_ptr)

    38 

    39 template <bool B, typename T = void>

    40 struct EnableIf: AllStatic {};

    41 

    42 template <typename T>

    43 struct EnableIf<true, T>: AllStatic {

    44   typedef T type;

    45 };

    46 

    47 #endif // SHARE_VM_METAPROGRAMMING_ENABLEIF_HPP