What are Object Initializers and Collection Initializers in C#?

Object Initializers

Object initializers facilitates assignment of values to any accessible fields or properties of an object at creation time, without having to explicitly invoke a constructor.

Object initializers with named types

In this example, we use auto-implemented properties to define a class.

public class Point
{
    public int iXPoint { get; set; }
    public int iYPoint { get; set; }
} 

During instantiation of the objects of the Point class, we can use:

Point oPoint = new Point();
oPoint.iXPoint = 0;
oPoint.iYPoint = 1;

Given below is a shorter technique to implement the above declaration and assignments:

// {iXPoint = 0, iYPoint = 1} is field or property assignments
Point oPoint = new Point { iXPoint = 0, iYPoint = 1 };  

In LINQ, we can use named object initializer as given below:

The following example shows the technique to use named object initializer with LINQ. The example below assumes that an object contains many fields and methods related to a product, but we are only interested in creating a sequence of objects that contain the product name and the unit price.

 var productInfos =
      from p in products
      select new { ProductName = p.ProductName, UnitPrice = p.UnitPrice };  

Collection Initializers

Collection Initializers are similar in concept to Object Initializers and allows you to create and initialize a collection in a single step. During implementation of a collection initializer, you do not have to specify multiple calls to the Add method of the class in your source code; the compiler adds the calls by itself.

List<int> numbers = new List<int> { 1, 100, 100 };

In fact, it is the short form of the following:

List<int> numbers = new List<int>();
numbers.Add(1);
numbers.Add(10);
numbers.Add(100); 

Note: To be able to use a Collection Initializer on an object, the object must satisfy these two requirements:

• It must implement the IEnumerable interface.
• It must have a public Add() method.