Monday, October 04, 2004

Difference between Value Type and Reference Types

When your code defines a variable of a reference type, the variable is either a reference to an object or it is a null reference. In contrast, a variable of a value type is the actual data, and no reference is involved.  Many programming languages provide built-in data types such as integers and floating-point numbers. These are copied when they are passed in to arguments i.e. they are passed "By Value". In .NET terms, these are called Value Types".

The RunTime supports two kinds of Value Types:

1 Built-in value types

The .NET Framework defines built-in value types such as System.Int32 and System.Boolean which correspond and are identical to primitive data types used in programming languages.

2 User-defined value types

The language you are using will provide functionality to define your own Value Types. These user defined Types derive from System.ValueType. If you want to define a Type representing a value that is a complex number (two floating-point numbers), you might choose to define it as a value type. Because you can pass the Value Type efficiently "By Value".

If the Type you are defining could be more efficiently passed "By Reference", you should define it as a class instead. Variables of Reference Types are referred to as objects. These store references to the actual data.

The following are the Reference Types:

  • class
  • interface
  • delegate

This following are the "built-in" Reference Types:

  • object
  • string
 Have a look into this article which deals about common type system in detail....

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