When should you use C# indexers?

Question

I'd like to use indexers more, but I'm not sure when to use them. All I've found online are examples that use classes like MyClass and IndexerClass.

What about in a school system where there are Students and Teachers, and each Teacher has a list of Students that they're in charge of - any need for indexers in that scenario? For simplicity's sake: each Student can only belong to one Teacher.

Answer 1

Indexer is a highly specialized property which allows instances of a class (or struct) to be indexed just like an array (properties can be static but indexers cannot).

Why to use indexers:

• instead of a new data structure, the class itself is a data structure.
• simplified syntax - syntactic sugar

When to use:

• if your class needs list(/array) of its instances (example 1)
• if your class represents list(/array) of values directly related to your class (example 2)

Example 1:

public class Person{
    public string Name{get; set;}
    
    private Person[] _backingStore;
    public Person this[int index]
    {
        get{
            return _backingStore[index];
        }
        set{
            _backingStore[index] = value;
        }
    }
}

Person p = new Person();
p[0] = new Person(){Name = "Hassan"};
p[1] = new Person(){Name = "John Skeet"};    

Example 2:

class TempratureRecord{
    private float[] temps = new float[10] { 56.2F, 56.7F, 56.5F, 56.9F, 58.8F, 61.3F, 56.5F, 56.9F, 58.8F, 61.3F};

    public int Length{
        get { return temps.Length; }
    }

    public float this[int index]
    {
        get{
            return temps[index];
        }
        set{
            temps[index] = value;
        }
    }
}

Answer 2

Heres a video i have created http://www.youtube.com/watch?v=HdtEQqu0yOY and below is a detailed explanation about the same.

Indexers helps to access contained collection with in a class using a simplified interface. It’s a syntactic sugar.

For instance lets say you have a customer class with addresses collection inside it. Now let’s say we would like to like fetch the addresses collection by “Pincode” and “PhoneNumber”. So the logical step would be that you would go and create two overloaded functions one which fetches by using “PhoneNumber” and the other by “PinCode”. You can see in the below code we have two functions defined.

Customer Customers = new Customer();
Customers.getAddress(1001);
Customers.getAddress("9090");

If you use indexer you can simplify the above code with something as shown in the below code.

Customer Customers = new Customer();
Address o = Customers[10001];
o = Customers["4320948"];

Cheers.