Collection Initializer in .Net Framework 3.0 onwards. Collection initializer gives a simple syntax to create instance of a collection.

  1. Collection initializer is new feature of C# 3.0.
  2. Collection initializer gives a simple syntax to create instance of a collection.
  3. Any object that is implementing System.Collections.Generic.ICollection<T>can be initialized with collection initializer.
Let us say, we have a class

Student.cs

1public class Student
2{
3    public string FirstName { get; set; }
4    public string LastName { get; set; }
5}

Now if we want to make collection of this class and add items of type student in that collection and retrieve through the collection, we need to write below code

Program.cs

01using System;
02using System.Collections.Generic;
03using System.Linq;
04using System.Text;
05namespace ConsoleApplication16
06{
07    class Program
08    {
09        static void Main(string[] args)
10        {
11            List<Student> lstStudent = newList<Student>();
12            Student std = newStudent();
13            std.FirstName = "Dhananjay";
14            std.LastName = "Kumar ";
15            lstStudent.Add(std);
16            std = newStudent();
17            std.FirstName = "Mritunjay ";
18            std.LastName = "Kumar";
19            lstStudent.Add(std);
20            foreach (Student resstd in lstStudent)
21            {
22                Console.WriteLine(resstd.FirstName);
23            }
24            Console.Read();
25        }
26 
27    }
28}


Output
image1.gif

In above code,

  1. An instance of List of Student is getting created.
  2. An instance of the Student is getting created.
  3. Using the Add method on the list, instance of being added to list of students.
  4. Using For each statement iterating through the list to get the values.
Now, if instance of Student class can be assigned to List of student at the time of creation of instance of list then we call it automatic collection initializer.

image2.gif
If we see the above syntax

  1. It is highly readable.
  2. It is single statement.
  3. Instance of Student class is getting added on the fly.
And we can retrieve the values as below, 

image3.gif

In retrieving implicit type local variable is being used to fetch the different instance of the student in list of student 

01List<Student> lstStudent = newList<Student>()
02{
03     newStudent{FirstName ="Dhananjay" ,LastName="Kumar"},
04     newStudent {FirstName ="Mritunjay", LastName ="Kumar"}
05};
06foreach (var r in lstStudent)
07{
08     Console.WriteLine(r.FirstName);
09}
10Console.Read();

Output
image4.gif

How it internally works?

A collection initializer invokes the ICollection<T>.Add(T) method for each specified element in order. In the above example , it will call 

ICollection<Student>.Add(instance of Student )