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What are generics? Generics permit classes, structs, interfaces, delegates, and methods to be parameterized by the types of data they store and manipulate. Why generics? To well know the useful of generics lets examine the following code:--
We use the object type to store any type of data. The above simple Stack class stores its data in an object array, and its two methods, Push and Pop, use object to accept and return data. While the use of type object makes the Stack class very flexible, it is not without drawbacks. For example, it is possible to push a value of any type, such a Customer instance, onto a stack. However, when a value is retrieved, the result of the Pop method must explicitly be cast back to the appropriate type, which is tedious to write and carries a performance penalty for run-time type checking:
If a value of a value type, such as an int, is passed to the Push method, it is automatically boxed. When the int is later retrieved, it must be unboxed with an explicit type cast:
Such boxing and unboxing operations add performance overhead since they involve dynamic memory allocations and run-time type checks.
While the code above is an improper use of the Stack class, the code is technically speaking correct and a compile-time error is not reported. The problem does not become apparent until the code is executed, at which point an InvalidCastException is thrown.
When the generic class Stack<T> is used, the actual type to substitute for T is specified. In the following example, int is given as the type argument for T:
The Stack<int> type is called a constructed type. In the Stack<int> type, every occurrence of T is replaced with the type argument int. When an instance of Stack<int> is created, the native storage of the items array is an int[] rather than object[], providing substantial storage efficiency compared to the non-generic Stack. Likewise, the Push and Pop methods of a Stack<int> operate on int values, making it a compile-time error to push values of other types onto the stack, and eliminating the need to explicitly cast values back to their original type when they抮e retrieved.
It was a breif introduction to generics that will be included in the next version of C# (V 2.0) . which is available now on its beta version with Visual C# 2005 Express Edition Beta 1. |
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