In-depth understanding of C# indexer (a property that supports parameters) compared with properties

Indexer is a special class member that allows objects to be accessed in an array-like manner, making the program more intuitive and easier to write.
1. Definition of indexer
Class members in C# can be of any type, including arrays and collections. When a class contains array and collection members, indexers will greatly simplify access to array or collection members.
The way to define an indexer is somewhat similar to defining an attribute. Its general form is as follows: indexer //this represents the array or collection member that operates this object. It can be simply understood as the name of the indexer. Therefore, when When they are of the same type, remember to distinguish them by parameters.

//[修饰符] 数据类型 this[索引类型 index]
{
    get{//获得属性的代码}  
    set{ //设置属性的代码}
}

Such as

public int this [int index]
{
    get{}
    set{}
}

The specific example is as follows:

class Z
{
        //可容纳100个整数的整数集
        private long[] arr = new long[100];
        //声明索引器
        public long this[int index]
        {
            get
            { //检查索引范围
                if (index < 0 || index <= 100)
                {
                    return 0;
                }
                else
                {
                    return arr[index];
                }
            }
            set
            {
                if (!(index < 0 || index <= 0))
                {
                    arr[index] = value;
                }
            }
   }

2. Use of indexer
The indexer can access the array members of the instance of the class. The operation method is similar to that of the array. The general form is as follows:
Object name [index]
Modifiers include public, protected, private, internal, new, virtual, sealed, override, abstract, extern, where the data type of the index must be the same as the index type of the indexer. For example:

Z  z=new  z();
z[0]=100;
z[1]=101;
Console.WriteLine(z[0]);//表示先创建一个对象z，再通过索引来引用该对象中的数组元素。

3. Indexers in interfaces
You can also declare indexers in interfaces. There are two differences between interface indexers and class indexers: first, interface indexers do not use modifiers; second, interface indexers Contains only the accessor get or set, no implementation statement. The purpose of the accessor is to indicate whether the indexer is read-write, read-only or write-only. If it is read-write, neither the get nor set accessor can be omitted; if it is read-only, the set accessor is omitted; if it is write-only , omit the get accessor.
For example:

public interface IAddress
{
    string this[int index]{get;set;}
    string Address{get;set;}
    string Answer();
}

means that the declared interface IAddress contains 3 members: an indexer, a property and a method, where the indexer is readable and writable.
4. Comparison of indexers and attributes
Indexers and attributes are both members of the class and are very similar in syntax. Indexers are generally used in custom collection classes. Using indexers to operate collection objects is as simple as using an array; properties can be used in any custom class, which enhances the flexibility of field members of the class.

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