michael@0: /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
michael@0:  * vim: set shiftwidth=4 tabstop=8 autoindent cindent expandtab: */
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
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #ifndef nsAutoRef_h_
michael@0: #define nsAutoRef_h_
michael@0: 
michael@0: #include "mozilla/Attributes.h"
michael@0: 
michael@0: #include "nscore.h" // for nullptr, bool
michael@0: 
michael@0: template <class T> class nsSimpleRef;
michael@0: template <class T> class nsAutoRefBase;
michael@0: template <class T> class nsReturnRef;
michael@0: template <class T> class nsReturningRef;
michael@0: 
michael@0: /**
michael@0:  * template <class T> class nsAutoRef
michael@0:  *
michael@0:  * A class that holds a handle to a resource that must be released.
michael@0:  * No reference is added on construction.
michael@0:  *
michael@0:  * No copy constructor nor copy assignment operators are available, so the
michael@0:  * resource will be held until released on destruction or explicitly
michael@0:  * |reset()| or transferred through provided methods.
michael@0:  *
michael@0:  * The publicly available methods are the public methods on this class and its
michael@0:  * public base classes |nsAutoRefBase<T>| and |nsSimpleRef<T>|.
michael@0:  *
michael@0:  * For ref-counted resources see also |nsCountedRef<T>|.
michael@0:  * For function return values see |nsReturnRef<T>|.
michael@0:  *
michael@0:  * For each class |T|, |nsAutoRefTraits<T>| or |nsSimpleRef<T>| must be
michael@0:  * specialized to use |nsAutoRef<T>| and |nsCountedRef<T>|.
michael@0:  *
michael@0:  * @param T  A class identifying the type of reference held by the
michael@0:  *           |nsAutoRef<T>| and the unique set methods for managing references
michael@0:  *           to the resource (defined by |nsAutoRefTraits<T>| or
michael@0:  *           |nsSimpleRef<T>|).
michael@0:  *
michael@0:  *           Often this is the class representing the resource.  Sometimes a
michael@0:  *           new possibly-incomplete class may need to be declared.
michael@0:  *
michael@0:  *
michael@0:  * Example:  An Automatically closing file descriptor
michael@0:  *
michael@0:  * // References that are simple integral types (as file-descriptors are)
michael@0:  * // usually need a new class to represent the resource and how to handle its
michael@0:  * // references.
michael@0:  * class nsRawFD;
michael@0:  *
michael@0:  * // Specializing nsAutoRefTraits<nsRawFD> describes how to manage file
michael@0:  * // descriptors, so that nsAutoRef<nsRawFD> provides automatic closing of
michael@0:  * // its file descriptor on destruction.
michael@0:  * template <>
michael@0:  * class nsAutoRefTraits<nsRawFD> {
michael@0:  * public:
michael@0:  *     // The file descriptor is held in an int.
michael@0:  *     typedef int RawRef;
michael@0:  *     // -1 means that there is no file associated with the handle.
michael@0:  *     static int Void() { return -1; }
michael@0:  *     // The file associated with a file descriptor is released with close().
michael@0:  *     static void Release(RawRef aFD) { close(aFD); }
michael@0:  * };
michael@0:  *
michael@0:  * // A function returning a file descriptor that must be closed.
michael@0:  * nsReturnRef<nsRawFD> get_file(const char *filename) {
michael@0:  *     // Constructing from a raw file descriptor assumes ownership.
michael@0:  *     nsAutoRef<nsRawFD> fd(open(filename, O_RDONLY));
michael@0:  *     fcntl(fd, F_SETFD, FD_CLOEXEC);
michael@0:  *     return fd.out();
michael@0:  * }
michael@0:  *
michael@0:  * void f() {
michael@0:  *     unsigned char buf[1024];
michael@0:  *
michael@0:  *     // Hold a file descriptor for /etc/hosts in fd1.
michael@0:  *     nsAutoRef<nsRawFD> fd1(get_file("/etc/hosts"));
michael@0:  *
michael@0:  *     nsAutoRef<nsRawFD> fd2;
michael@0:  *     fd2.steal(fd1); // fd2 takes the file descriptor from fd1
michael@0:  *     ssize_t count = read(fd1, buf, 1024); // error fd1 has no file
michael@0:  *     count = read(fd2, buf, 1024); // reads from /etc/hosts
michael@0:  *
michael@0:  *     // If the file descriptor is not stored then it is closed.
michael@0:  *     get_file("/etc/login.defs"); // login.defs is closed
michael@0:  *
michael@0:  *     // Now use fd1 to hold a file descriptor for /etc/passwd.
michael@0:  *     fd1 = get_file("/etc/passwd");
michael@0:  *
michael@0:  *     // The nsAutoRef<nsRawFD> can give up the file descriptor if explicitly
michael@0:  *     // instructed, but the caller must then ensure that the file is closed.
michael@0:  *     int rawfd = fd1.disown();
michael@0:  *
michael@0:  *     // Assume ownership of another file descriptor.
michael@0:  *     fd1.own(open("/proc/1/maps");
michael@0:  *
michael@0:  *     // On destruction, fd1 closes /proc/1/maps and fd2 closes /etc/hosts,
michael@0:  *     // but /etc/passwd is not closed.
michael@0:  * }
michael@0:  *
michael@0:  */
michael@0: 
michael@0: 
michael@0: template <class T>
michael@0: class nsAutoRef : public nsAutoRefBase<T>
michael@0: {
michael@0: protected:
michael@0:     typedef nsAutoRef<T> ThisClass;
michael@0:     typedef nsAutoRefBase<T> BaseClass;
michael@0:     typedef nsSimpleRef<T> SimpleRef;
michael@0:     typedef typename BaseClass::RawRefOnly RawRefOnly;
michael@0:     typedef typename BaseClass::LocalSimpleRef LocalSimpleRef;
michael@0: 
michael@0: public:
michael@0:     nsAutoRef()
michael@0:     {
michael@0:     }
michael@0: 
michael@0:     // Explicit construction is required so as not to risk unintentionally
michael@0:     // releasing the resource associated with a raw ref.
michael@0:     explicit nsAutoRef(RawRefOnly aRefToRelease)
michael@0:         : BaseClass(aRefToRelease)
michael@0:     {
michael@0:     }
michael@0: 
michael@0:     // Construction from a nsReturnRef<T> function return value, which expects
michael@0:     // to give up ownership, transfers ownership.
michael@0:     // (nsReturnRef<T> is converted to const nsReturningRef<T>.)
michael@0:     explicit nsAutoRef(const nsReturningRef<T>& aReturning)
michael@0:         : BaseClass(aReturning)
michael@0:     {
michael@0:     }
michael@0: 
michael@0:     // The only assignment operator provided is for transferring from an
michael@0:     // nsReturnRef smart reference, which expects to pass its ownership to
michael@0:     // another object.
michael@0:     //
michael@0:     // With raw references and other smart references, the type of the lhs and
michael@0:     // its taking and releasing nature is often not obvious from an assignment
michael@0:     // statement.  Assignment from a raw ptr especially is not normally
michael@0:     // expected to release the reference.
michael@0:     //
michael@0:     // Use |steal| for taking ownership from other smart refs.
michael@0:     //
michael@0:     // For raw references, use |own| to indicate intention to have the
michael@0:     // resource released.
michael@0:     //
michael@0:     // Or, to create another owner of the same reference, use an nsCountedRef.
michael@0: 
michael@0:     ThisClass& operator=(const nsReturningRef<T>& aReturning)
michael@0:     {
michael@0:         BaseClass::steal(aReturning.mReturnRef);
michael@0:         return *this;
michael@0:     }
michael@0: 
michael@0:     // Conversion to a raw reference allow the nsAutoRef<T> to often be used
michael@0:     // like a raw reference.
michael@0:     operator typename SimpleRef::RawRef() const
michael@0:     {
michael@0:         return this->get();
michael@0:     }
michael@0: 
michael@0:     // Transfer ownership from another smart reference.
michael@0:     void steal(ThisClass& aOtherRef)
michael@0:     {
michael@0:         BaseClass::steal(aOtherRef);
michael@0:     }
michael@0: 
michael@0:     // Assume ownership of a raw ref.
michael@0:     //
michael@0:     // |own| has similar function to |steal|, and is useful for receiving
michael@0:     // ownership from a return value of a function.  It is named differently
michael@0:     // because |own| requires more care to ensure that the function intends to
michael@0:     // give away ownership, and so that |steal| can be safely used, knowing
michael@0:     // that it won't steal ownership from any methods returning raw ptrs to
michael@0:     // data owned by a foreign object.
michael@0:     void own(RawRefOnly aRefToRelease)
michael@0:     {
michael@0:         BaseClass::own(aRefToRelease);
michael@0:     }
michael@0: 
michael@0:     // Exchange ownership with |aOther|
michael@0:     void swap(ThisClass& aOther)
michael@0:     {
michael@0:         LocalSimpleRef temp;
michael@0:         temp.SimpleRef::operator=(*this);
michael@0:         SimpleRef::operator=(aOther);
michael@0:         aOther.SimpleRef::operator=(temp);
michael@0:     }
michael@0: 
michael@0:     // Release the reference now.
michael@0:     void reset()
michael@0:     {
michael@0:         this->SafeRelease();
michael@0:         LocalSimpleRef empty;
michael@0:         SimpleRef::operator=(empty);
michael@0:     }
michael@0: 
michael@0:     // Pass out the reference for a function return values.
michael@0:     nsReturnRef<T> out()
michael@0:     {
michael@0:         return nsReturnRef<T>(this->disown());
michael@0:     }
michael@0: 
michael@0:     // operator->() and disown() are provided by nsAutoRefBase<T>.
michael@0:     // The default nsSimpleRef<T> provides get().
michael@0: 
michael@0: private:
michael@0:     // No copy constructor
michael@0:     explicit nsAutoRef(ThisClass& aRefToSteal);
michael@0: };
michael@0: 
michael@0: /**
michael@0:  * template <class T> class nsCountedRef
michael@0:  *
michael@0:  * A class that creates (adds) a new reference to a resource on construction
michael@0:  * or assignment and releases on destruction.
michael@0:  *
michael@0:  * This class is similar to nsAutoRef<T> and inherits its methods, but also
michael@0:  * provides copy construction and assignment operators that enable more than
michael@0:  * one concurrent reference to the same resource.
michael@0:  *
michael@0:  * Specialize |nsAutoRefTraits<T>| or |nsSimpleRef<T>| to use this.  This
michael@0:  * class assumes that the resource itself counts references and so can only be
michael@0:  * used when |T| represents a reference-counting resource.
michael@0:  */
michael@0: 
michael@0: template <class T>
michael@0: class nsCountedRef : public nsAutoRef<T>
michael@0: {
michael@0: protected:
michael@0:     typedef nsCountedRef<T> ThisClass;
michael@0:     typedef nsAutoRef<T> BaseClass;
michael@0:     typedef nsSimpleRef<T> SimpleRef;
michael@0:     typedef typename BaseClass::RawRef RawRef;
michael@0: 
michael@0: public:
michael@0:     nsCountedRef()
michael@0:     {
michael@0:     }
michael@0: 
michael@0:     // Construction and assignment from a another nsCountedRef
michael@0:     // or a raw ref copies and increments the ref count.
michael@0:     nsCountedRef(const ThisClass& aRefToCopy)
michael@0:     {
michael@0:         SimpleRef::operator=(aRefToCopy);
michael@0:         SafeAddRef();
michael@0:     }
michael@0:     ThisClass& operator=(const ThisClass& aRefToCopy)
michael@0:     {
michael@0:         if (this == &aRefToCopy)
michael@0:             return *this;
michael@0: 
michael@0:         this->SafeRelease();
michael@0:         SimpleRef::operator=(aRefToCopy);
michael@0:         SafeAddRef();
michael@0:         return *this;
michael@0:     }
michael@0: 
michael@0:     // Implicit conversion from another smart ref argument (to a raw ref) is
michael@0:     // accepted here because construction and assignment safely creates a new
michael@0:     // reference without interfering with the reference to copy.
michael@0:     explicit nsCountedRef(RawRef aRefToCopy)
michael@0:         : BaseClass(aRefToCopy)
michael@0:     {
michael@0:         SafeAddRef();
michael@0:     }
michael@0:     ThisClass& operator=(RawRef aRefToCopy)
michael@0:     {
michael@0:         this->own(aRefToCopy);
michael@0:         SafeAddRef();
michael@0:         return *this;
michael@0:     }
michael@0: 
michael@0:     // Construction and assignment from an nsReturnRef function return value,
michael@0:     // which expects to give up ownership, transfers ownership.
michael@0:     explicit nsCountedRef(const nsReturningRef<T>& aReturning)
michael@0:         : BaseClass(aReturning)
michael@0:     {
michael@0:     }
michael@0:     ThisClass& operator=(const nsReturningRef<T>& aReturning)
michael@0:     {
michael@0:         BaseClass::operator=(aReturning);
michael@0:         return *this;
michael@0:     }
michael@0: 
michael@0: protected:
michael@0:     // Increase the reference count if there is a resource.
michael@0:     void SafeAddRef()
michael@0:     {
michael@0:         if (this->HaveResource())
michael@0:             this->AddRef(this->get());
michael@0:     }
michael@0: };
michael@0: 
michael@0: /**
michael@0:  * template <class T> class nsReturnRef
michael@0:  *
michael@0:  * A type for function return values that hold a reference to a resource that
michael@0:  * must be released.  See also |nsAutoRef<T>::out()|.
michael@0:  */
michael@0: 
michael@0: template <class T>
michael@0: class nsReturnRef : public nsAutoRefBase<T>
michael@0: {
michael@0: protected:
michael@0:     typedef nsAutoRefBase<T> BaseClass;
michael@0:     typedef typename BaseClass::RawRefOnly RawRefOnly;
michael@0: 
michael@0: public:
michael@0:     // For constructing a return value with no resource
michael@0:     nsReturnRef()
michael@0:     {
michael@0:     }
michael@0: 
michael@0:     // For returning a smart reference from a raw reference that must be
michael@0:     // released.  Explicit construction is required so as not to risk
michael@0:     // unintentionally releasing the resource associated with a raw ref.
michael@0:     explicit nsReturnRef(RawRefOnly aRefToRelease)
michael@0:         : BaseClass(aRefToRelease)
michael@0:     {
michael@0:     }
michael@0: 
michael@0:     // Copy construction transfers ownership
michael@0:     nsReturnRef(nsReturnRef<T>& aRefToSteal)
michael@0:         : BaseClass(aRefToSteal)
michael@0:     {
michael@0:     }
michael@0: 
michael@0:     nsReturnRef(const nsReturningRef<T>& aReturning)
michael@0:         : BaseClass(aReturning)
michael@0:     {
michael@0:     }
michael@0: 
michael@0:     // Conversion to a temporary (const) object referring to this object so
michael@0:     // that the reference may be passed from a function return value
michael@0:     // (temporary) to another smart reference.  There is no need to use this
michael@0:     // explicitly.  Simply assign a nsReturnRef<T> function return value to a
michael@0:     // smart reference.
michael@0:     operator nsReturningRef<T>()
michael@0:     {
michael@0:         return nsReturningRef<T>(*this);
michael@0:     }
michael@0: 
michael@0:     // No conversion to RawRef operator is provided on nsReturnRef, to ensure
michael@0:     // that the return value is not carelessly assigned to a raw ptr (and the
michael@0:     // resource then released).  If passing to a function that takes a raw
michael@0:     // ptr, use get or disown as appropriate.
michael@0: };
michael@0: 
michael@0: /**
michael@0:  * template <class T> class nsReturningRef
michael@0:  *
michael@0:  * A class to allow ownership to be transferred from nsReturnRef function
michael@0:  * return values.
michael@0:  *
michael@0:  * It should not be necessary for clients to reference this
michael@0:  * class directly.  Simply pass an nsReturnRef<T> to a parameter taking an
michael@0:  * |nsReturningRef<T>|.
michael@0:  *
michael@0:  * The conversion operator on nsReturnRef constructs a temporary wrapper of
michael@0:  * class nsReturningRef<T> around a non-const reference to the nsReturnRef.
michael@0:  * The wrapper can then be passed as an rvalue parameter.
michael@0:  */
michael@0: 
michael@0: template <class T>
michael@0: class nsReturningRef
michael@0: {
michael@0: private:
michael@0:     friend class nsReturnRef<T>;
michael@0: 
michael@0:     explicit nsReturningRef(nsReturnRef<T>& aReturnRef)
michael@0:         : mReturnRef(aReturnRef)
michael@0:     {
michael@0:     }
michael@0: public:
michael@0:     nsReturnRef<T>& mReturnRef;
michael@0: };
michael@0: 
michael@0: /**
michael@0:  * template <class T> class nsAutoRefTraits
michael@0:  *
michael@0:  * A class describing traits of references managed by the default
michael@0:  * |nsSimpleRef<T>| implementation and thus |nsAutoRef<T>| and |nsCountedRef|.
michael@0:  * The default |nsSimpleRef<T> is suitable for resources with handles that
michael@0:  * have a void value.  (If there is no such void value for a handle,
michael@0:  * specialize |nsSimpleRef<T>|.)
michael@0:  *
michael@0:  * Specializations must be provided for each class |T| according to the
michael@0:  * following pattern:
michael@0:  *
michael@0:  * // The template parameter |T| should be a class such that the set of fields
michael@0:  * // in class nsAutoRefTraits<T> is unique for class |T|.  Usually the
michael@0:  * // resource object class is sufficient.  For handles that are simple
michael@0:  * // integral typedefs, a new unique possibly-incomplete class may need to be
michael@0:  * // declared.
michael@0:  *
michael@0:  * template <>
michael@0:  * class nsAutoRefTraits<T>
michael@0:  * {
michael@0:  *     // Specializations must provide a typedef for RawRef, describing the
michael@0:  *     // type of the handle to the resource.
michael@0:  *     typedef <handle-type> RawRef;
michael@0:  *
michael@0:  *     // Specializations should define Void(), a function returning a value
michael@0:  *     // suitable for a handle that does not have an associated resource.
michael@0:  *     //
michael@0:  *     // The return type must be a suitable as the parameter to a RawRef
michael@0:  *     // constructor and operator==.
michael@0:  *     //
michael@0:  *     // If this method is not accessible then some limited nsAutoRef
michael@0:  *     // functionality will still be available, but the default constructor,
michael@0:  *     // |reset|, and most transfer of ownership methods will not be available.
michael@0:  *     static <return-type> Void();
michael@0:  *
michael@0:  *     // Specializations must define Release() to properly finalize the
michael@0:  *     // handle to a non-void custom-deleted or reference-counted resource.
michael@0:  *     static void Release(RawRef aRawRef);
michael@0:  *
michael@0:  *     // For reference-counted resources, if |nsCountedRef<T>| is to be used,
michael@0:  *     // specializations must define AddRef to increment the reference count
michael@0:  *     // held by a non-void handle.
michael@0:  *     // (AddRef() is not necessary for |nsAutoRef<T>|.)
michael@0:  *     static void AddRef(RawRef aRawRef);
michael@0:  * };
michael@0:  *
michael@0:  * See nsPointerRefTraits for example specializations for simple pointer
michael@0:  * references.  See nsAutoRef for an example specialization for a non-pointer
michael@0:  * reference.
michael@0:  */
michael@0: 
michael@0: template <class T> class nsAutoRefTraits;
michael@0: 
michael@0: /**
michael@0:  * template <class T> class nsPointerRefTraits
michael@0:  *
michael@0:  * A convenience class useful as a base class for specializations of
michael@0:  * |nsAutoRefTraits<T>| where the handle to the resource is a pointer to |T|.
michael@0:  * By inheriting from this class, definitions of only Release(RawRef) and
michael@0:  * possibly AddRef(RawRef) need to be added.
michael@0:  *
michael@0:  * Examples of use:
michael@0:  *
michael@0:  * template <>
michael@0:  * class nsAutoRefTraits<PRFileDesc> : public nsPointerRefTraits<PRFileDesc>
michael@0:  * {
michael@0:  * public:
michael@0:  *     static void Release(PRFileDesc *ptr) { PR_Close(ptr); }
michael@0:  * };
michael@0:  *
michael@0:  * template <>
michael@0:  * class nsAutoRefTraits<FcPattern> : public nsPointerRefTraits<FcPattern>
michael@0:  * {
michael@0:  * public:
michael@0:  *     static void Release(FcPattern *ptr) { FcPatternDestroy(ptr); }
michael@0:  *     static void AddRef(FcPattern *ptr) { FcPatternReference(ptr); }
michael@0:  * };
michael@0:  */
michael@0: 
michael@0: template <class T>
michael@0: class nsPointerRefTraits
michael@0: {
michael@0: public:
michael@0:     // The handle is a pointer to T.
michael@0:     typedef T* RawRef;
michael@0:     // A nullptr does not have a resource.
michael@0:     static RawRef Void() { return nullptr; }
michael@0: };
michael@0: 
michael@0: /**
michael@0:  * template <class T> class nsSimpleRef
michael@0:  *
michael@0:  * Constructs a non-smart reference, and provides methods to test whether
michael@0:  * there is an associated resource and (if so) get its raw handle.
michael@0:  *
michael@0:  * A default implementation is suitable for resources with handles that have a
michael@0:  * void value.  This is not intended for direct use but used by |nsAutoRef<T>|
michael@0:  * and thus |nsCountedRef<T>|.
michael@0:  *
michael@0:  * Specialize this class if there is no particular void value for the resource
michael@0:  * handle.  A specialized implementation must also provide Release(RawRef),
michael@0:  * and, if |nsCountedRef<T>| is required, AddRef(RawRef), as described in
michael@0:  * nsAutoRefTraits<T>.
michael@0:  */
michael@0: 
michael@0: template <class T>
michael@0: class nsSimpleRef : protected nsAutoRefTraits<T>
michael@0: {
michael@0: protected:
michael@0:     // The default implementation uses nsAutoRefTrait<T>.
michael@0:     // Specializations need not define this typedef.
michael@0:     typedef nsAutoRefTraits<T> Traits;
michael@0:     // The type of the handle to the resource.
michael@0:     // A specialization must provide a typedef for RawRef.
michael@0:     typedef typename Traits::RawRef RawRef;
michael@0: 
michael@0:     // Construct with no resource.
michael@0:     //
michael@0:     // If this constructor is not accessible then some limited nsAutoRef
michael@0:     // functionality will still be available, but the default constructor,
michael@0:     // |reset|, and most transfer of ownership methods will not be available.
michael@0:     nsSimpleRef()
michael@0:         : mRawRef(Traits::Void())
michael@0:     {
michael@0:     }
michael@0:     // Construct with a handle to a resource.
michael@0:     // A specialization must provide this. 
michael@0:     nsSimpleRef(RawRef aRawRef)
michael@0:         : mRawRef(aRawRef)
michael@0:     {
michael@0:     }
michael@0: 
michael@0:     // Test whether there is an associated resource.  A specialization must
michael@0:     // provide this.  The function is permitted to always return true if the
michael@0:     // default constructor is not accessible, or if Release (and AddRef) can
michael@0:     // deal with void handles.
michael@0:     bool HaveResource() const
michael@0:     {
michael@0:         return mRawRef != Traits::Void();
michael@0:     }
michael@0: 
michael@0: public:
michael@0:     // A specialization must provide get() or loose some functionality.  This
michael@0:     // is inherited by derived classes and the specialization may choose
michael@0:     // whether it is public or protected.
michael@0:     RawRef get() const
michael@0:     {
michael@0:         return mRawRef;
michael@0:     }
michael@0: 
michael@0: private:
michael@0:     RawRef mRawRef;
michael@0: };
michael@0: 
michael@0: 
michael@0: /**
michael@0:  * template <class T> class nsAutoRefBase
michael@0:  *
michael@0:  * Internal base class for |nsAutoRef<T>| and |nsReturnRef<T>|.
michael@0:  * Adds release on destruction to a |nsSimpleRef<T>|.
michael@0:  */
michael@0: 
michael@0: template <class T>
michael@0: class nsAutoRefBase : public nsSimpleRef<T>
michael@0: {
michael@0: protected:
michael@0:     typedef nsAutoRefBase<T> ThisClass;
michael@0:     typedef nsSimpleRef<T> SimpleRef;
michael@0:     typedef typename SimpleRef::RawRef RawRef;
michael@0: 
michael@0:     nsAutoRefBase()
michael@0:     {
michael@0:     }
michael@0: 
michael@0:     // A type for parameters that should be passed a raw ref but should not
michael@0:     // accept implicit conversions (from another smart ref).  (The only
michael@0:     // conversion to this type is from a raw ref so only raw refs will be
michael@0:     // accepted.)
michael@0:     class RawRefOnly
michael@0:     {
michael@0:     public:
michael@0:         RawRefOnly(RawRef aRawRef)
michael@0:             : mRawRef(aRawRef)
michael@0:         {
michael@0:         }
michael@0:         operator RawRef() const
michael@0:         {
michael@0:             return mRawRef;
michael@0:         }
michael@0:     private:
michael@0:         RawRef mRawRef;
michael@0:     };
michael@0: 
michael@0:     // Construction from a raw ref assumes ownership
michael@0:     explicit nsAutoRefBase(RawRefOnly aRefToRelease)
michael@0:         : SimpleRef(aRefToRelease)
michael@0:     {
michael@0:     }
michael@0: 
michael@0:     // Constructors that steal ownership
michael@0:     explicit nsAutoRefBase(ThisClass& aRefToSteal)
michael@0:         : SimpleRef(aRefToSteal.disown())
michael@0:     {
michael@0:     }
michael@0:     explicit nsAutoRefBase(const nsReturningRef<T>& aReturning)
michael@0:         : SimpleRef(aReturning.mReturnRef.disown())
michael@0:     {
michael@0:     }
michael@0: 
michael@0:     ~nsAutoRefBase()
michael@0:     {
michael@0:         SafeRelease();
michael@0:     }
michael@0: 
michael@0:     // An internal class providing access to protected nsSimpleRef<T>
michael@0:     // constructors for construction of temporary simple references (that are
michael@0:     // not ThisClass).
michael@0:     class LocalSimpleRef : public SimpleRef
michael@0:     {
michael@0:     public:
michael@0:         LocalSimpleRef()
michael@0:         {
michael@0:         }
michael@0:         explicit LocalSimpleRef(RawRef aRawRef)
michael@0:             : SimpleRef(aRawRef)
michael@0:         {
michael@0:         }
michael@0:     };
michael@0: 
michael@0: private:
michael@0:     ThisClass& operator=(const ThisClass& aSmartRef) MOZ_DELETE;
michael@0:     
michael@0: public:
michael@0:     RawRef operator->() const
michael@0:     {
michael@0:         return this->get();
michael@0:     }
michael@0: 
michael@0:     // Transfer ownership to a raw reference.
michael@0:     //
michael@0:     // THE CALLER MUST ENSURE THAT THE REFERENCE IS EXPLICITLY RELEASED.
michael@0:     //
michael@0:     // Is this really what you want to use?  Using this removes any guarantee
michael@0:     // of release.  Use nsAutoRef<T>::out() for return values, or an
michael@0:     // nsAutoRef<T> modifiable lvalue for an out parameter.  Use disown() when
michael@0:     // the reference must be stored in a POD type object, such as may be
michael@0:     // preferred for a namespace-scope object with static storage duration,
michael@0:     // for example.
michael@0:     RawRef disown()
michael@0:     {
michael@0:         RawRef temp = this->get();
michael@0:         LocalSimpleRef empty;
michael@0:         SimpleRef::operator=(empty);
michael@0:         return temp;
michael@0:     }
michael@0: 
michael@0: protected:
michael@0:     // steal and own are protected because they make no sense on nsReturnRef,
michael@0:     // but steal is implemented on this class for access to aOtherRef.disown()
michael@0:     // when aOtherRef is an nsReturnRef;
michael@0: 
michael@0:     // Transfer ownership from another smart reference.
michael@0:     void steal(ThisClass& aOtherRef)
michael@0:     {
michael@0:         own(aOtherRef.disown());
michael@0:     }
michael@0:     // Assume ownership of a raw ref.
michael@0:     void own(RawRefOnly aRefToRelease)
michael@0:     {
michael@0:         SafeRelease();
michael@0:         LocalSimpleRef ref(aRefToRelease);
michael@0:         SimpleRef::operator=(ref);
michael@0:     }
michael@0: 
michael@0:     // Release a resource if there is one.
michael@0:     void SafeRelease()
michael@0:     {
michael@0:         if (this->HaveResource())
michael@0:             this->Release(this->get());
michael@0:     }
michael@0: };
michael@0: 
michael@0: #endif // !defined(nsAutoRef_h_)