Type System Unification in C# .NET

Last Updated : 06 May, 2019

The Type System Unification in C# means all the data types in C# are inherited from the Object class, whether directly or indirectly. Or you can say all types are considered as objects. In C#, primitive types are known as the Value Types which are basically structs. Internally, structs and classes inherit the Object Class. That’s why all types are indirectly considered as Objects, and this terminology is known as Type System Unification.

Example: All the predefined types (like short, int long etc.) are structs. Below are predefined types along with their struct equivalents:

Predefined Type	Equivalent Struct
short	System.Int16
int	System.Int32
long	System.Int64
ushort	System.UInt16
uint	System.UInt32
ulong	System.Int64
byte	System.Byte
sbyte	System.SByte
bool	System.Boolean
char	System.Char
Float	System.Single
Double	System.Double
Decimal	System.Decimal

Example: In the below program, the value data types such as int, char, bool are used as objects because of type system unification with the method ToString() that returns a string representing that particular object.

// C# implementation of Type  
// System Unification 
using System; 
  
class GFG { 
  
    // Main Method 
    public static void Main(string[] args) 
    { 
        // Value data types 
        int i = 1; 
        char c = 'A'; 
        bool b = true; 
  
        Console.WriteLine(i.ToString()); 
        Console.WriteLine(c.ToString()); 
        Console.WriteLine(b.ToString()); 
    } 
} 

Output:

1
A
True

Boxing and Unboxing

Type System Unification enables boxing and unboxing as any value data type can be treated as an object. So, when a value data type such as int, char, bool, etc. is converted into an object type, it is known as boxing. Conversely, when the object type is converted back into the data type, it is known as unboxing.

Boxing: A value data type such as int, char, bool, etc. is converted into an object type implicitly in boxing. First, an object type is allocated and then the value in the value data type is copied into the object type.

Example:

// C# implementation of Boxing 
using System; 
  
class GFG { 
  
    // Main Method 
    static public void Main() 
    { 
        // int value data type 
        int val = 8; 
  
        // boxing 
        object obj = val; 
  
        System.Console.WriteLine("val = {0}", val); 
        System.Console.WriteLine("obj = {0}", obj); 
    } 
} 

Output:

val = 8
obj = 8

Unboxing: An object type is converted into a value data type such as int, char, bool, etc. explicitly in unboxing. First, it is checked if the object type is the boxed value of the value data type. If yes, then the value in the object type is copied out of it.

Example:

// C# implementation of Unboxing 
using System; 
  
class GFG { 
  
    // Main Method 
    static public void Main() 
    { 
        // int value data type 
        int val1 = 8; 
  
        // boxing 
        object obj = val1; 
  
        // unboxing 
        int val2 = (int)obj; 
  
        Console.WriteLine("val1 = " + val1); 
        Console.WriteLine("obj = " + obj); 
        Console.WriteLine("val2 = " + val2); 
    } 
} 

Output:

val1 = 8
obj = 8
val2 = 8

Benefits of Type System Unification: The Type System Unification is quite useful as it provides the dual benefit of a data type behaving as a value data type or an object type. A value data type can be used when required and it can be converted into an object type using boxing if required because of the inherent characteristic of Type System Unification.