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CFilterOutputStageCreator

Name

CFilterOutputStageCreator -- Create filter output stages for CFilterOutputStageFactory

Synopsis


#include <CFilterOutputStageCreator.h>

class CFilterOutputStageCreator
{
public:
  virtual CFilterOutputStage*  operator()(std::string type) = 0;
  virtual std::string document() const = 0;
  virtual CFilterOutputStageCreator* clone() = 0;
};

DESCRIPTION

This is an abstract base class that creates objects on behalf of the CFilterOutputStageFactory extensible factory. Concrete classes of this type create specific output stage objects. This is one of the keys to providing an extensible Filter subsystsem. To add a new filter output stage type only requires that you write a filter output stage, a creator for that output stage and register that creator with the Filter output stage factcory singleton.

This class defines the interface that is required of a concrete filter output stage creator.

METHODS

virtual = 0 CFilterOutputStage* operator()(std::string type);

Concrete classes must implement this to respond to their filter type by returning a pointer to a newly created instance of a filter output stage. If the type is not recognized, the creator should return a nullptr.

Naturally care must be taken by authors of filter output stage creators not to recognize strings that are already recognized by other formatters.

virtual const = 0 std::string document();

Returns a string that documents the type of output stage created by this creator. This is used by the filter command to provide a list of available filter formats.

To line up properly, the string returned should be of the form: 


                1         2         3
      col:  0123456789012345678901234567890
            type      - description

virtual = 0 CFilterOutputStageCreator* clone();

There are situations when the filter output stage factor must create a copy of an existing creator given a pointer to it with type CFilterOutputStageCreator*. The clone method provides support for it. The method should return a pointer to a new instance of a duplicate of the object it is called on.

If a creator implements copy construction, the simplest way to do this is: 


CFilterOutputStageCreator*
CMyOutputStageCreator::clone()
{
   return new CMyOutputStageCreator(*this);
}

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