An Example of Generics Using C# in ASP.Net

When you run this code you get a return value from the method.

As you saw in the previous example there is an array list of integer values and get the result as expected but now add one more value to the ArrayList that the data type is float and perform the same Addition operation. Let's see the updated code in the following snippet.

In the code above, all three values are easily added to the array list because the ArrayList class Add() method values are an object type but when retrieving the values using each statement each value will be assigned an int data type variable but this array list has a combination of both integer and float type value and float values won't cast to an int implicitly. That is why the code will give the exception “Specified cast is not valid.” That means that an ArrayList is not type safe. What this means is that an ArrayList can be assigned a value of any type.

Generics allow you to realize type safety at compile time. They allow you to create a data structure without committing to a specific data type. When the data structure is used, however, the compiler ensures that the types used with it are consistent for type safety. Generics provide type safety, but without any loss of performance or code bloat. The System.Collections.Generics namespace contains the generics collections. Now let's see an example with a generic collection List.

In the code above we define a list int type, in other words we can only add an integer value to the list and can't add a float value to it so when we retrieve values from the list using a foreach statement we only get an int value. When you run this code you will get a return value from the method. Now you can say that a generic collection is type safe.

Performance

Before discussing performance we need to understand object data types in C#, so what are object data types? From the MSDN “The object type is an alias for Object in the .NET Framework. In the unified type system of C#, all types, predefined and user-defined, reference types and value types, inherit directly or indirectly from Object. You can assign values of any type to variables of the type object. When a variable of a value type is converted to an object, it is said to be boxed. When a variable of type object is converted to a value type, it is said to be unboxed.” I hope it make sense.

Before generics, the way to define a generalized algorithm was to define its entire member to the Object data type. If you wanted to use the algorithm with value type instances, the CLR needed to box the value type instance prior to calling the members of the algorithm. This boxing causes memory allocations on the managed heap, that causes more frequent garbage collections, which, in turn, hurt an application's performance.

Since a generic algorithm can now be created to work with a specific value type, the instances of the value type can be passed by value, and the CLR no longer must do any boxing. In addition, since casts are not necessary, the CLR doesn't need to check the type safety of the attempted cast, and this results in faster code too.

Now let's see the syntax of the Add() method for non-generic and generic collection classes. We are discussing two collection classes, one for non-generic (ArrayList) and another is generic (List).

the syntax of the Add() method of ArrayList:

The preceding line of method signature represents that each value to be added to an ArrayList will be an object type, in other words if you are using a value type to be added to an ArrayList then it will be cast yo an object type before being added to ArrayList.

The syntax of the Add() method of List<T>:

The preceding line of method signature represents that there is no need to do a cast to add an item to a generic type list. If the List type is T then the item will be T type.

Now you understand who has better performance. A generic collection class has better performance than a non-generic collection class. Let's see an example in the following code snippet.