wtf/PossiblyNull.h

   1 /*
   2  * Copyright (C) 2009 Apple Inc. All Rights Reserved.
   3  *
   4  * Redistribution and use in source and binary forms, with or without
   5  * modification, are permitted provided that the following conditions
   6  * are met:
   7  * 1. Redistributions of source code must retain the above copyright
   8  *    notice, this list of conditions and the following disclaimer.
   9  * 2. Redistributions in binary form must reproduce the above copyright
  10  *    notice, this list of conditions and the following disclaimer in the
  11  *    documentation and/or other materials provided with the distribution.
  12  *
  13  * THIS SOFTWARE IS PROVIDED BY APPLE INC. ``AS IS'' AND ANY
  14  * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  15  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  16  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL APPLE INC. OR
  17  * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
  18  * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
  19  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
  20  * PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY
  21  * OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  23  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #ifndef PossiblyNull_h
  27 #define PossiblyNull_h
  28
  29 #include "Assertions.h"
  30
  31 namespace WTF {
  32
  33 template <typename T> struct PossiblyNull {
  34     PossiblyNull(T data)
  35         : m_data(data)
  36     {
  37     }
  38     PossiblyNull(const PossiblyNull<T>& source)
  39         : m_data(source.m_data)
  40     {
  41         source.m_data = 0;
  42     }
  43     ~PossiblyNull() { ASSERT(!m_data); }
  44     bool getValue(T& out) WARN_UNUSED_RETURN;
  45 private:
  46     mutable T m_data;
  47 };
  48
  49 template <typename T> bool PossiblyNull<T>::getValue(T& out)
  50 {
  51     out = m_data;
  52     bool result = !!m_data;
  53     m_data = 0;
  54     return result;
  55 }
  56
  57 }
  58
  59 #endif