Smart Pointers

Detailed Description

collection of smart pointers as ScopedPtr, SharedPtr, ...

Author

Bram de Greve [Bramz]

Pointers

• lass::util::ScopedPtr: a smart pointer for single ownership, deallocates on end of scope.
• lass::util::SharedPtr: a smart pointer for shared ownership, keeping track of reference count.
• lass::util::SmartI: a smart pointer to COM interfaces.

StoragePolicy

Storage polices control how the pointees are stored in the smart pointer and how they should be deallocated. Two default storage policies are provided for objects allocated by new and arrays allocated by new[], but it should be possible to write special storage policies to embed other smart pointers in our lass::util smart pointer classes.

concept of storage policy

All storage policies should implement the following interface. Some functions like at(size_t) should only be implemented for array-like pointees. So they can safely be ommited if pointee does not act like an array.

template <typename T>
class StoragePolicy
{
public:
 
    typedef ... TStorage;   // the type of the storage_ object (usually T*)
    typedef ... TPointer;   // return type of pointer() or operator-> (usually T*)
    typedef ... TReference; // return type of operator* or operator[] (usually T&)
 
    TStorage& storage();
    // return reference to storage object (usualy to a pointer)
 
    const TStorage& storage() const;
    // return const-reference to storage object
 
protected:
 
    StoragePolicy();
    // should initialize with default storage object (in most cases: NULL)
 
    StoragePolicy(T* pointee);
    // should initialize to store given pointee.
 
    TPointer pointer() const;
    // should return a pointer to the pointee
 
    TReference at(size_t iIndex) const;
    // for arrays only: should return reference to iIndex'th object in array
    // (YOU CAN OMMIT THIS FOR NON-ARRAYS)
 
    void dispose();
    // deallocate the pointee (e.g. by a delete or delete [])
 
    bool isNull() const;
    // return true if storage contains equivalent of NULL pointer.
 
    void swap(StoragePolicy<T>& other);
    // swap storage object with other policy.
};

implemenated models of storage policy

• lass::util::ObjectStorage: simple storage policy for objects allocated by new.
• lass::util::ArrayStorage: simple storage policy for arrays allocated by new[].

CounterPolicy

Counter policies control how reference counting should be done. In contrary to the storage policies, this is only used by the SharedPtr.

concept of counter policy

All counter policies should implement the following interface. The template parameter TStorage is of the same type as TStorage in the used storage policy. It will useually be a pointer to the pointee.

class CounterPolicy
{
public:
 
    typedef ... TCount; // type of reference counter variable (should be an integer)
 
protected:
 
    DefaultCounter(); // brings object in valid state without setting any counter.
 
    template <typename TStorage> void init(TStorage& pointee);
    // initialize reference count one one.  This is called on acquring of object by first owner
    // (increment isn't called for first owner).
 
    template <typename TStorage> void dispose(TStorage& pointee);
    // clean up the counter (not the pointee).  This is called when reference count drops to
    // zero (thus on release by last owner).
 
    template <typename TStorage> void increment(TStorage& pointee);
    // increment the reference count by one.  This is called on acquiring of object by any owner
    // except the first (the first one calls init(TStorage&) instead).
 
    template <typename TStorage> bool decrement(TStorage& pointee);
    // decrement the reference count by one and returns true if it drops below one.  This is
    // called on every release of the object by any owner.  It should return true if @e after
    // the decrement the reference count turns out the be less than one (i.e. there are no more
    // owners, this was the last one), to indicate the pointee should be deallocated now.  In
    // all other cases, it should return false @e after the (i.e. if the reference count is
    // still non-zero after the decrement).
 
    template <typename TStorage> TCount count(TStorage& pointee) const;
    // return the reference count, i.e. number of owners of the pointee
 
    void swap(DefaultCounter& other);
    // swap any reference counters with other policy.
};

implemenated models of counter policy

• lass::util::DefaultCounter: allocates extra counter on heap to keep track of reference count.
• lass::util::IntrusiveCounter: uses a member of the object as reference count.

Data Structures
class	lass::util::SmartI< I >
	smart pointer to COM interfaces More...
class	lass::util::ObjectStorage< T, Cascade >
	Default storage policy for single objects, implementation of StoragePolicy concept. More...
class	lass::util::ArrayStorage< T, Cascade >
	Default storage policy for arrays, implementation of StoragePolicy concept. More...
class	lass::util::DefaultCounter
	The default counter for the shared pointers, implementation of CounterPolicy concept. More...
class	lass::util::IntrusiveCounter< T, CounterType, referenceCounter >
	implementation of CounterPolicy concept, using a counter in the managed object itself. More...