Index initializers

Download c# eBook

Example

Index initializers make it possible to create and initialize objects with indexes at the same time.

This makes initializing Dictionaries very easy:

var dict = new Dictionary<string, int>()
{
    ["foo"] = 34,
    ["bar"] = 42
};

Any object that has an indexed getter or setter can be used with this syntax:

class Program
{
    public class MyClassWithIndexer
    {
        public int this[string index]
        {
            set
            {
                Console.WriteLine($"Index: {index}, value: {value}");
            }
        }
    }

    public static void Main()
    {
        var x = new MyClassWithIndexer()
        {
            ["foo"] = 34,
            ["bar"] = 42
        };

        Console.ReadKey();
    }
}

Output:

Index: foo, value: 34
Index: bar, value: 42

View Demo

If the class has multiple indexers it is possible to assign them all in a single group of statements:

class Program
{
    public class MyClassWithIndexer
    {
        public int this[string index]
        {
            set
            {
                Console.WriteLine($"Index: {index}, value: {value}");
            }
        }
        public string this[int index]
        {
            set
            {
                Console.WriteLine($"Index: {index}, value: {value}");
            }
        }
    }

    public static void Main()
    {
        var x = new MyClassWithIndexer()
        {
            ["foo"] = 34,
            ["bar"] = 42,
            [10] = "Ten",
            [42] = "Meaning of life"
        };
    }
}

Output:

Index: foo, value: 34
Index: bar, value: 42
Index: 10, value: Ten
Index: 42, value: Meaning of life

It should be noted that the indexer set accessor might behave differently compared to an Add method (used in collection initializers).

For example:

var d = new Dictionary<string, int>
{
    ["foo"] = 34,
    ["foo"] = 42,
}; // does not throw, second value overwrites the first one

versus:

var d = new Dictionary<string, int>
{
    { "foo", 34 },
    { "foo", 42 },
}; // run-time ArgumentException: An item with the same key has already been added.

Stats

Contributors: 9
2016-08-15
Licensed under: CC-BY-SA

Not affiliated with Stack Overflow
Rip Tutorial: info@zzzprojects.com

Download eBook