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"You know you've achieved perfection in design, not when you have nothing more to add, but when you have nothing more to take away." Antoine de Saint-Exupery
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Null Object

A proposito di Nullable types vorrei segnalare due cose:

1. un commento interessante di Anders Hejlsberg via un post di Krzysztof Cwalina, PM CLR:

"When you design APIs using Nullable<T>, you have to be very sensitive to the fact that a Nullable<T> is a lot less convenient to use than a T. Nullable<T> with value types makes sense and solves a real world problem--therefore, users will be amenable to the inconveniences of using it. However, Nullable<T> with reference types makes little sense and solves no real world problem. In fact, it adds nothing but confusion because, in terms capabilities, there is no difference between a string and a Nullable<string>. With respect to having a Value Type constraint on Nullable<T>, we haven't done it because it would severely limit Nullable<T>'s use in generic scenarios. For example, imagine a Find method that returns a T or a null value when an item isn't found. In the generic world, a possible solution is to return Nullable<T>, but only if Nullable<T> works for all types";

2. un Nullable type che ho trovato nel framework CSLA.NET di Rockford Lhotka come la classe CSLA.SmartDate.

In realtà i tipi Nullable sono suggeriti da un design pattern proposto da Bobby Woolf nel 1996 come Null Object, caso particolare di un altro pattern, Special Case

Print | posted on venerdì 26 marzo 2004 01:15 | Filed Under [ Pattern Dappertutto ]

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