1 // Copyright 2014 The Chromium Authors. All rights reserved. 2 // Use of this source code is governed by a BSD-style license that can be 3 // found in the LICENSE file. 4 5 #ifndef Nullable_h 6 #define Nullable_h 7 8 #include "platform/heap/Handle.h" 9 #include "wtf/Assertions.h" 10 11 namespace blink { 12 13 template <typename T> 14 class Nullable { 15 DISALLOW_ALLOCATION(); 16 public: Nullable()17 Nullable() 18 : m_value() 19 , m_isNull(true) { } 20 Nullable(const T & value)21 Nullable(const T& value) 22 : m_value(value) 23 , m_isNull(false) { } 24 Nullable(const Nullable & other)25 Nullable(const Nullable& other) 26 : m_value(other.m_value) 27 , m_isNull(other.m_isNull) { } 28 29 Nullable& operator=(const Nullable& other) 30 { 31 m_value = other.m_value; 32 m_isNull = other.m_isNull; 33 return *this; 34 } 35 set(const T & value)36 void set(const T& value) 37 { 38 m_value = value; 39 m_isNull = false; 40 } get()41 const T& get() const { ASSERT(!m_isNull); return m_value; } get()42 T& get() { ASSERT(!m_isNull); return m_value; } isNull()43 bool isNull() const { return m_isNull; } 44 45 // See comment in RefPtr.h about what UnspecifiedBoolType is. 46 typedef const T* UnspecifiedBoolType; UnspecifiedBoolType()47 operator UnspecifiedBoolType() const { return m_isNull ? 0 : &m_value; } 48 49 bool operator==(const Nullable& other) const 50 { 51 return (m_isNull && other.m_isNull) || (!m_isNull && !other.m_isNull && m_value == other.m_value); 52 } 53 trace(Visitor * visitor)54 void trace(Visitor* visitor) 55 { 56 TraceIfNeeded<T>::trace(visitor, &m_value); 57 } 58 59 private: 60 T m_value; 61 bool m_isNull; 62 }; 63 64 } // namespace blink 65 66 #endif // Nullable_h 67