LManagedPtr Class Reference

Detailed Description

A class template that provides automatic management of pointers held in the data members of objects.

By default, the cleanup action is to delete the managed pointer using a (non-array) delete operation. An alternative cleanup strategy can be specified using the optional CleanupStrategy class template parameter of the LManagedPtr class template. The most common alternative cleanup strategies are predefined (e.g. TPointerFree).

The constructors of this class never leave, so data members defined with this type may be initialized safely during any phase of construction of the owning class.

As a convenience, the methods of the managed pointer may be accessed via "->" notation directly on the management object, while "." notation is used to access the interface of the management object itself. Using "*" to dereference the management object yields a T&, and is often useful when passing the managed object as an argument.

Automatic cleanup may be disabled at any time by calling Unmanage(), while cleanup may be forced at any time by calling ReleaseResource().

   class CComposite : public CBase
	   {
	 public:
	   CONSTRUCTORS_MAY_LEAVE

	   CComposite()
		   : iComponent(CComponent::NewL())
		   {
		   //...
		   }

	   ~CComposite()
		   {
		   // the pointer to the CComponent object is automatically
		   // deleted
		   }

	 private:
	   LManagedPtr<CComponent> iComponent;
	   };

Behind the scenes, this class template simply relies on reliable execution of its destructor. If used for a local variable rather than a data member, cleanup will occur but out-of-order compared to objects protected using the LCleanupXxx variants or the CleanupStack directly. Therefore it is not recommended for use in that context.

These management classes may be used as the basis for implementing leave-safe single-phase construction, since fully initialized data members protected in this way will get destroyed (so reliably triggering cleanup) if their containing classes leave during execution of their constructors. Note, however, that single-phase construction must be explicitly enabled in the containing class using the CONSTRUCTORS_MAY_LEAVE macro.

This class template together with the cleanup strategy class templates provide a template-based implementation of the Strategy design pattern (See also: Policy-based design).

See also: TPointerDelete which implements the default deleting cleanup strategy TPointerFree which implements the alternative User::Free() cleanup strategy LCleanedupPtr which has the same interface, but uses the cleanup stack and is suitable for protecting locals CONSTRUCTORS_MAY_LEAVE