What is the meaning of `public string this[string columnName]` When implementing IDataErrorInfo interface?

Question

What is the meaning of public string this[string columnName] When implementing IDataErrorInfo interface?

    public string this[string columnName]
    {
        get
        {
            switch (columnName)
            {
                case "Name":
                    return ValidateName();
                case "PhoneNumber":
                    return ValidatePhoneNumber();
                default:
                    return string.Empty;
            }
        }
    }

I don't get it why there are square parentheses and what it does.

---

Answer: Thanks to Hans and Scott now I know that is simply the syntax of an indexer. More information here.

Delius

What specifically do you not understand the this[string columnName] syntax or are you asking why they do it at all? – Nose

Look in your favorite C# language book for "indexer". – Symphonic

You have to understand IDataErrorInfo, and then you will understand the meaning of This[columnName], and I think this is why you got a downvote. – Weinman

@ScottChamberlain: the syntax. I don't get it why there are square parentheses and what id does. – Delius

@HansPassant: thanks, I will check it out. – Delius

this was closed???? – Baroness

Answer 1

That is a C# indexer, it lets you use your class like

IDataErrorInfo myClass = new MyClass();
string phoneNumberErrorInfo = myClass["PhoneNumber"];`

Nose

To the person who downvoted me, what about my answer was incorrect or not useful? I can't fix my question if you don't tell me what I have done wrong. – Nose