Detailed introduction to several uses of new in C#

This article mainly introduces several usages of new in C#, which has good reference value. Let’s take a look at it with the editor

In C#, the new keyword Can be used as an operator, modifier, or constraint.

new operator

is used to create objects and call constructors .

new modifier

is used to hide inherited members from base class members.

new Constraints

are used to constrain the types of parameters that may be used as type parameters in a generic declaration.

new modifier (C# reference)

When used as a modifier, the new keyword can explicitly hide members inherited from the base class. Hiding an inherited member means that the derived version of the member replaces the base class version. Hiding members without the new modifier is allowed, but a warning is generated. Explicitly hiding a member using new suppresses this warning and logs the fact that the derived version is used instead.

To hide an inherited member, declare the member in the derived class with the same name and modify the member with the new modifier

new operator (C# Reference)

#1. Used to create objects and call constructors. For example:

Class1 o = new Class1();

2. Also used to call the default constructor for value types

Example :int myInt = new int();

MyInt is initialized to 0, which is the default value of the int type. The effect of this statement is equivalent to: int myInt = 0;

3. The new operator cannot be overloaded.

4. If the new operator fails to allocate memory, it will throw an OutOfMemoryException exception

new Constraints (C# Reference)

new The constraint specifies that any type parameter in a generic class declaration must have a public parameterless constructor. When a generic class creates a new instance of the type, this constraint is applied to the type parameters, as shown in the following example:

class ItemFactory<T> where T : new() 
{ 
public T GetNewItem() 
{ 
return new T(); 
} 
}

Hiding names through inheritance takes one of the following forms:

　1 .Introducing a constant, designation, attribute, or type into a class or structure hides all base class members with the same name.

　2. The method introduced in the class or structure hides the properties, fields and types with the same name in the base class. Also hides all base class methods with the same signature.

　3. The indexer introduced in a class or structure will hide all base class indexers with the same name.

　4. It is wrong to use new and override at the same time on the same member.

Note: Using the new modifier in a declaration that does not hide inherited members will generate a warning.

　Example

　In this example, the nested class MyClass hides classes with the same name in the base class. This example not only illustrates how to use fully qualified names to access hidden class members, but also illustrates how to use the new modifier to suppress warning messages.

　　 using System; 
　　 public class MyBaseC 
　　 { 
　　 public class MyClass 
　　 { 
　　 public int x = 200; 
　　 public int y; 
　　 } 
　　 } 
　　 public class MyDerivedC : MyBaseC 
　　 { 
　　 new public class MyClass // nested type hiding the base type members 
　　 { 
　　 public int x = 100; 
　　 public int y; 
　　 public int z; 
　　 } 
　　 public static void Main() 
　　{ 
　　 // Creating object from the overlapping class: 
　　 MyClass S1 = new MyClass(); 
　　 // Creating object from the hidden class: 
　 MyBaseC.MyClass S2 = new MyBaseC.MyClass(); 
　　 Console.WriteLine(S1.x); 
　　 Console.WriteLine(S2.x); 
　　 } 
　　 } 

　　输出
　　100
　　200

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