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// This is mul/mbl/mbl_data_wrapper.h
#ifndef mbl_data_wrapper_h
#define mbl_data_wrapper_h
#ifdef VCL_NEEDS_PRAGMA_INTERFACE
#pragma interface
#endif
//:
// \file
// \author Tim Cootes
// \brief A wrapper to provide access to sets of objects
//: Base class for objects which can return a set of objects, one at a time
// This is an iterator-like object. However, unlike STL, generality is
// obtained by deriving from the class rather than providing a similar
// interface.
//
// In particular one can query the object to find out how many examples
// to expect.
//
// A typical use is to allow clients to build
// models from sets of data without having to hold all the data in memory
// at once.
//
// Example:
// \code
// vnl_vector<double> my_sum(mbl_data_wrapper<vnl_vector<double> >& data)
// {
// data.reset();
// vnl_vector<double> sum = data.current();
// while (data.next())
// sum += data.current();
// }
// \endcode
//
// Note: It should be fairly simple to provide an iterator type object
// which steps through the examples in a standard STL way by using this class.
#include <vcl_string.h>
template<class T>
class mbl_data_wrapper
{
public:
//: Default constructor
mbl_data_wrapper();
//: Default destructor
virtual ~mbl_data_wrapper();
//: Number of objects available
virtual unsigned long size() const = 0;
//: Reset so that current() returns first object
virtual void reset() = 0;
//: Return current object
virtual const T& current() = 0;
//: Move to next object, returning true if is valid
virtual bool next() = 0;
//: Return current index
// First example has index 0
virtual unsigned long index() const =0;
//: Move to element n
// First example has index 0
virtual void set_index(unsigned long n);
//: Create copy on heap and return base pointer
// This will create an independent iterator on the underlying data.
// The original data is not copied.
// Be careful of destruction of underlying data.
virtual mbl_data_wrapper< T >* clone() const = 0;
//: Name of the class
virtual vcl_string is_a() const =0;
//: True if this is (or is derived from) class named s
virtual bool is_class(vcl_string const& s) const =0;
};
#endif // mbl_data_wrapper_h
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