Basic C# class question regarding the “this” keyword

Question

I'm going through someone else's code and I saw this statement:

public CustomClassName this [ string varName]

Please excuse the newbness of this question, but the square brackets threw me off. Is this a method or constructor?

How does the "this" variable work in this case?

Answer 1

It's called an indexer. MSDN page.

Answer 2

它是一个索引器，因此您可以访问类似于数组的类。

Answer 3

It is defining an index operator on your type. Take for example, the List<T> class. The library designers wanted you to be able to write code like this:

List<int> list = new List<int> { 1, 2, 3, 4, 5 };
int x = list[2]; // x == 3

The syntax that accomplishes that is what you have posted above. So, for your own types, you can...

class NameCollection : /* whatever */
{
    private List<string> _names = new List<string> { "Ed", "Sally", "John" };

    public string this[int index]
    {
        get { return _names[index]; }
    }
}

Answer 4

this is simply an overload of the square-bracket operator in C#.

see here:

How do I overload the square-bracket operator in C#?

Answer 5

Neither, it's an Indexer . It allows you to do CustomClassName[ obj ] and retrieve a value from the object.