itpp::Factory Class Reference

Base class for class factories. More...

#include <itpp/base/factory.h>

Inheritance diagram for itpp::Factory:

Public Member Functions
	Factory ()
	Default constructor.
virtual	~Factory ()
	Destructor.

Detailed Description

Base class for class factories.

A class factory (or virtual constructor) is a class that can create instances of another class. Factory is a base class for such factories. When declaring an Array, Vec or Mat, a factory can be passed as an (optional) constructor argument:

// Declare a Vec<type> with size=10 and factory=DEFAULT_FACTORY
Vec<type> a(10);

// Declare a Vec<type> with size=10 and factory=f
Factory f;
Vec<type> b(10, f);

By default, the factory (DEFAULT_FACTORY and f in the above examples) is not used at all! However, by overloading a help function called create_elements we can force Array/Vec/Mat to use the factory for element creation (instead of using the default constructor for the element type).

Note

It is the numeric elements that will be created by the factory, i.e. for an Array<Mat<T> >, the factory will be used for creating the Mat elements rather than the Array elements.

Here is an example that (partly) defines a user-defined numeric type My_Type, a corresponding factory My_Factory and a corresponding help function create_elements<My_Type> that will be used by Array, Vec and Mat for element creation.

class My_Type {
public:
// Default constructor
My_Type() : data(0) {}
// Constructor
My_Type(int d) : data(d) {}
.
.
.
protected:
int data;
};

class My_Factory : public Factory {
public:
// Constructor
explicit My_Factory(int d) : init_data(d) {}
// Destructor
virtual ~My_Factory() {}
// Create an n-length array of My_Type
virtual void create(My_Type* &ptr, int n) const {ptr = new My_Type[n](init_data);}
protected:
int init_data;
};

// Create an n-length array of My_Type using My_Factory f
template<>
void create_elements<My_Type>(My_Type* &ptr, int n, const Factory &f)
{
if (const My_Factory *my_factory_ptr = dynamic_cast<const My_Factory*>(&f)) {
// Yes, f seems to be a My_Factory. Now call the My_Factory::create method
my_factory_ptr->create(ptr, n);
}
else {
// No, f does not seem to be a My_Factory. As a fallback solution,
// assume that f is DEFAULT_FACTORY and use the default constructor
ptr = new My_Type[n];
}
}

Now,

// Declare a My_Factory for init_data = 123
My_Factory my123_factory(123);

// Declare a Vec<My_Type> with size 10 that uses My_Type() for element creation
Vec<My_Type> v1(10);

// Declare a Vec<My_Type> with size 10 that uses My_Type(123) for element creation
Vec<My_Type> v1(10, my123_factory);

For a more interesting example, see Fix_Factory.

Definition at line 129 of file factory.h.

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The documentation for this class was generated from the following file:

• itpp/base/factory.h