michael@0: /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*-*/
michael@0: /* vim: set ts=2 sw=2 et tw=79: */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this file,
michael@0:  * You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifndef mozilla_dom_Nullable_h
michael@0: #define mozilla_dom_Nullable_h
michael@0: 
michael@0: #include "mozilla/Assertions.h"
michael@0: #include "nsTArrayForwardDeclare.h"
michael@0: #include "mozilla/Move.h"
michael@0: 
michael@0: namespace mozilla {
michael@0: namespace dom {
michael@0: 
michael@0: // Support for nullable types
michael@0: template <typename T>
michael@0: struct Nullable
michael@0: {
michael@0: private:
michael@0:   // mIsNull MUST COME FIRST because otherwise the casting in our array
michael@0:   // conversion operators would shift where it is found in the struct.
michael@0:   bool mIsNull;
michael@0:   T mValue;
michael@0: 
michael@0: public:
michael@0:   Nullable()
michael@0:     : mIsNull(true)
michael@0:   {}
michael@0: 
michael@0:   explicit Nullable(T aValue)
michael@0:     : mIsNull(false)
michael@0:     , mValue(aValue)
michael@0:   {}
michael@0: 
michael@0:   explicit Nullable(Nullable<T>&& aOther)
michael@0:     : mIsNull(aOther.mIsNull)
michael@0:     , mValue(mozilla::Move(aOther.mValue))
michael@0:   {}
michael@0: 
michael@0:   Nullable(const Nullable<T>& aOther)
michael@0:     : mIsNull(aOther.mIsNull)
michael@0:     , mValue(aOther.mValue)
michael@0:   {}
michael@0: 
michael@0:   void operator=(const Nullable<T>& aOther)
michael@0:   {
michael@0:     mIsNull = aOther.mIsNull;
michael@0:     mValue = aOther.mValue;
michael@0:   }
michael@0: 
michael@0:   void SetValue(T aValue) {
michael@0:     mValue = aValue;
michael@0:     mIsNull = false;
michael@0:   }
michael@0: 
michael@0:   // For cases when |T| is some type with nontrivial copy behavior, we may want
michael@0:   // to get a reference to our internal copy of T and work with it directly
michael@0:   // instead of relying on the copying version of SetValue().
michael@0:   T& SetValue() {
michael@0:     mIsNull = false;
michael@0:     return mValue;
michael@0:   }
michael@0: 
michael@0:   void SetNull() {
michael@0:     mIsNull = true;
michael@0:   }
michael@0: 
michael@0:   const T& Value() const {
michael@0:     MOZ_ASSERT(!mIsNull);
michael@0:     return mValue;
michael@0:   }
michael@0: 
michael@0:   T& Value() {
michael@0:     MOZ_ASSERT(!mIsNull);
michael@0:     return mValue;
michael@0:   }
michael@0: 
michael@0:   bool IsNull() const {
michael@0:     return mIsNull;
michael@0:   }
michael@0: 
michael@0:   bool Equals(const Nullable<T>& aOtherNullable) const
michael@0:   {
michael@0:     return (mIsNull && aOtherNullable.mIsNull) ||
michael@0:            (!mIsNull && !aOtherNullable.mIsNull &&
michael@0:             mValue == aOtherNullable.mValue);
michael@0:   }
michael@0: 
michael@0:   bool operator==(const Nullable<T>& aOtherNullable) const
michael@0:   {
michael@0:     return Equals(aOtherNullable);
michael@0:   }
michael@0: 
michael@0:   bool operator!=(const Nullable<T>& aOtherNullable) const
michael@0:   {
michael@0:     return !Equals(aOtherNullable);
michael@0:   }
michael@0: 
michael@0:   // Make it possible to use a const Nullable of an array type with other
michael@0:   // array types.
michael@0:   template<typename U>
michael@0:   operator const Nullable< nsTArray<U> >&() const {
michael@0:     // Make sure that T is ok to reinterpret to nsTArray<U>
michael@0:     const nsTArray<U>& arr = mValue;
michael@0:     (void)arr;
michael@0:     return *reinterpret_cast<const Nullable< nsTArray<U> >*>(this);
michael@0:   }
michael@0:   template<typename U>
michael@0:   operator const Nullable< FallibleTArray<U> >&() const {
michael@0:     // Make sure that T is ok to reinterpret to FallibleTArray<U>
michael@0:     const FallibleTArray<U>& arr = mValue;
michael@0:     (void)arr;
michael@0:     return *reinterpret_cast<const Nullable< FallibleTArray<U> >*>(this);
michael@0:   }
michael@0: };
michael@0: 
michael@0: } // namespace dom
michael@0: } // namespace mozilla
michael@0: 
michael@0: #endif /* mozilla_dom_Nullable_h */