Question

I have a class called Product in my Business object and in another class i want to return a list of objects of this class.Which approach i should use ?

public static List<Product> GetProductList() { .... }

or create another class in my Business object namspace called ProductList which extends List <Products> as follows:

public class ProductList :List<Products > { .... }

and use it there

public static ProductList GetProductList() { .... }

Is there any difference between these two ? How abt the memory allocation and performance ?

Answer 1

There is a small overhead in having an extra type (ProductList), but nothing huge. But it really depends on what you want to do. In many ways, ProductList is still a bad idea since it burns List<T> into the public API, and List<T> isn’t very extensible (none of the methods are virtual, for example). Collection<T> might have more extensibility options.

I’d argue in favor of abstraction or encapsulation:

public static IList<Product> GetProductList() {...} // abstraction; can return
                                                    // List<Product> if we want

or:

public class ProductList : IList<Product> {...} // encapsulation, but need to
                                                // add a lot of dull code

It is a shame that C# doesn’t make the encapsulation approach simple (I’m thinking “mixins”).

Note that another trick (sometimes suitable, sometimes not) would be to use extension methods to add the illusion of extra methods on IList<Product>… this is a tricky debate, so I’m just mentioning it, not saying “do this”.