Why can I initialize a List like an array in C#?

Question

Today I was surprised to find that in C# I can do:

List a = new List { 1, 2, 3 };

Why can I do this? What constructor

Answer 1

The array like syntax is being turned in a series of Add() calls.

To see this in a much more interesting example, consider the following code in which I do two interesting things that sound first illegal in C#, 1) setting a readonly property, 2) setting a list with a array like initializer.

public class MyClass
{   
    public MyClass()
    {   
        _list = new List();
    }
    private IList _list;
    public IList MyList 
    { 
        get
        { 
            return _list;
        }
    }
}
//In some other method
var sample = new MyClass
{
    MyList = {"a", "b"}
};

This code will work perfectly, although 1) MyList is readonly and 2) I set a list with array initializer.

The reason why this works, is because in code that is part of an object intializer the compiler always turns any {} like syntax to a series of Add() calls which are perfectly legal even on a readonly field.