C: readonly and Const

One 、const keyword

1.const Modifiable types

C# In the middle of const No, C++ So flexible , The types of variables that can be modified are very limited .

There are mainly these kinds ： Basic data type 、 String type 、 A fellow const The variable of

Illustrate with examples ：

    const float f=9;
    const string s = "999";
    const int i1 = 8;
    const int i2 = i1+1;

2. Note that

1）const You can modify not only member variables but also local variables .

2）const The principle of is to replace variable values directly at compile time .

3）const Decorated variables can no longer be used static Variable to modify , And it can only be initialized in the declaration of the field

This part mainly refers to ：const keyword - C# Reference resources | Microsoft Docs

C# Basic knowledge series 8 （const and readonly keyword ） - Xiaole - Blog Garden

Two 、readonly keyword

readonly Keywords compared to const Keywords are more flexible .

1. Instructions

1）readonly There are no restrictions on variable types . but readonly Modified keywords can only be used in Declaration period Or in the same class Constructors Assign values to fields . You can assign and reassign read-only fields multiple times in field declarations and constructors , At other times, it cannot be assigned .

Illustrate with examples ：

public class ReadOnlyTest : MonoBehaviour
{
    readonly int i = 0;// It can be assigned at the time of declaration 
    readonly float f1;// It is also possible not to assign values at the time of declaration 
    ReadOnlyTest()
    {
        i = 9;// Multiple assignments can be made in the constructor 
        i = 8;
        f1 = 2.2f;
    }
}

2）readonly Decorate value types and reference types .

public class RefType
{
    public int i = 0;
}
public struct ValueType
{
    public int i = 0;
    public ValueType(int a)
    {
         i=a;
    }
}
public class ReadOnlyTest : MonoBehaviour
{
    readonly RefType refType = new RefType();
    readonly ValueType valueType = new ValueType();
    readonly ValueType1 valueType1 = new ValueType1();// Report errors 
    void Test()
    {
        refType.i = 9;// Don't complain 
        valueType.i = 2;// Report errors 

    }
}

It can be seen that readonly The type of value decorated , The member variable of value type will also be readonly Of , But when decorating reference types , Its essence is a constant pointer , Member variables of reference types are not subject to readonly Modifier constrained .

2. Be careful

1）readonly Decorated variables are assigned at runtime .

2）readonly Cannot decorate general local variables , Currently tested , You know ref Follow readonly Connected together, you can decorate .

3）readonly The modified variable can be static Of

This part refers to ：readonly keyword - C# Reference resources | Microsoft Docs

C# Basic knowledge series 8 （const and readonly keyword ） - Xiaole - Blog Garden

3、 ... and 、 other

use readonly modification struct There are also other precautions , May refer to ：C# Read only structures in （readonly struct） Detailed explanation

however readonly It can't be modified class Of .