[LINQ via C# series]

Take this Person type as an example:

public class Person
{
    public string Name
    {
        get;
        set;
    }

    public int Age
    {
        get;
        set;
    }
}

Object initializer

In C# 2.0 we create an Person instance and initialize it like this:

Person person = new Person();
person.Name = "Mark";
person.Age = 18;

While in C# 3.0, we can use the object initializer syntactical shortcut:

Person person = new Person()
                    {
                        Name = "Mark",
                        Age = 18
                    };

This code will be compiled into:

Person <>g__initLocal0 = new Person();
<>g__initLocal0.Name = "Mark";
<>g__initLocal0.Age = 18;
Person person = <>g__initLocal0;

Collection initializer

In C# 2.0 we initialize an collection like this:

Collection<Person> persons = new Collection<Person>();
persons.Add(mark);
persons.Add(steven);

Now in C# 3.0 we can write code like this:

Collection<Person> persons = new Collection<Person>()
                                    {
                                        mark, 
                                        steven
                                    };

The compiler will look up the Add() method automatically:

Collection<Person> <>g__initLocal0 = new Collection<Person>();
<>g__initLocal0.Add(mark);
<>g__initLocal0.Add(steven);
Collection<Person> persons = <>g__initLocal0;

To use the collection initializer on a collection, these are needed to do:

• Implement System.IEnumerable for the collection type 
• Define a Add() instance method for the collection type. The method takes at least one parameter, and its return value is ignored

Here is a shortest sample. Collection initializer can be applied to the following collection:

public class PersonCollection : IEnumerable
{
    public void Add(Person person)
    {
    }

    public IEnumerator GetEnumerator()
    {
        throw new NotImplementedException();
    }
}

If the Add() method takes more than one parameters, this syntax should be used:

Dictionary<string, int> persons = new Dictionary<string, int>()
    {
        { "Mark", 18 }, // Compiled to Add("Mark", 18).
        { "Steven", 18 } // Compiled to Add("Steven", 18).
    };