.NET Framework CLR: What is the Common Type System?

[HanneSThEGreaT]

Q: What is the Common Type System?

A: The Common Type System (CTS) defines how types are declared, used and managed in the runtime, and is also an important part of the runtime's support for cross-language integration.

• What functions does the Common Type System perform?
  
  
  • Establishes a framework that helps enable cross-language integration, type safety, and high performance code execution.
    
    
  • Provides an object-oriented model that supports the complete implementation of many programming languages.
    
    
  • Defines rules that languages must follow, which helps ensure that objects written in different languages can interact with each other.
  
  
  
  
• What types does the Common Type System support?
  
  
  • Value types
    
    Value types directly contain their data, and instances of value types are either allocated on the stack or allocated inline in a structure. Value types can be built-in (implemented by the runtime), user-defined, or enumerations. For a list of built-in value types, see the .NET Framework Class Library.
    
    
  • Reference types
    
    Reference types store a reference to the value's memory address, and are allocated on the heap. Reference types can be self-describing types, pointer types, or interface types. The type of a reference type can be determined from values of self-describing types. Self-describing types are further split into arrays and class types. The class types are user-defined classes, boxed value types, and delegates.
  
  
  
  
• Can I have an example of the difference between value types and reference types?
  
  The following example shows the difference between reference types and value types:
  
  
  

  Imports System
  
  Class Class1
      Public Value As Integer = 0
  End Class 'Class1
  
  Class Test
      
      Shared Sub Main()
          Dim val1 As Integer = 0
          Dim val2 As Integer = val1
          val2 = 123
          Dim ref1 As New Class1()
          Dim ref2 As Class1 = ref1
          ref2.Value = 123
          Console.WriteLine("Values: {0}, {1}", val1, val2)
          Console.WriteLine("Refs: {0}, {1}", ref1.Value, ref2.Value)
      End Sub 'Main
  End Class 'Test

  
  
• What would the output be of the above example?
  
  Values: 0, 123
  Refs: 123, 123