C# 3.0 Features Basics For LINQ - PART 1

  • [アーティクル]

The 'var' Keyword

  1. Type inferred at compile time
  2. Can only be defined within method scope
  3. Mostly used when you need a variable for anonymous types which can only be resolved at compile time e.g. LINQ queries

Auto Implemented properties

This feature eases the creation of properties for a field inside the C# class e.g.

    1:  //C# 3.0 Code 

    2:  class Contact

    3:  {

    4:      public string Phone { get; set; }

    5:      public string Name { get; set; }

    6:  }

 In the above code, we create two properties.The compiler automatically creates a private variable here accessed only via getters and setters. 
In C# 2.0 we would write a considerably big code for achieving this : 

    1:  //C# 2.0 Code 

    2:  Class Contact { 

    3:   private string _name;

    4:   public String Name {

    5:      get {

    6:          If(_name != null )  {

    7:              return _name;

    8:          }

    9:      set {

   10:          _name = value;

   11:      }

   12:  }

  

Making Sense Of Object Initializers

In C# 3.0 you can use object initializers to assign values to accessible fields/properties at the time of object creation e.g.

    1:  // C# 3.0;Object initializer for our Contact class 

    2:  Contact myContact = new Contact { Phone = '1212', Name = 'Bindesh' };

This is useful when we want to use the anonymous types , since the only way to initialize them are using object initializers . It also helps in selecting a portion of the data that is needed from all the available data in an class e.g.

 

    1:  class Contact {

    2:      public string FirstName { get; set; }

    3:      public string LastName { get;set;}

    4:      public string  Email {get;set;}

    5:      public string Phone {get;set;}

    6:  }

    7:  var contact = from c in Contacts

    8:             select new { c.FirstName, c.LastName, c.Email } ;
Collection Initializers

As is the case with object initializers, you can also have the Collections initialized in a short way, like

    1:  //C# 3.0;Collections Initializer

    2:  List <Contact> contacts = new List <Contact> { 

    3:                                              {'Bindesh', 'Vijayan'},

    4:                                              {'Madhuban', 'Singh'},

    5:                                              {'Sukesh', 'A K'}

    6:                                           };

The same would have taken a considerable work in C# 2.0, e.g.

    1:  List<Contact> contacts = new List<Contact>();

    2:  //call Add each time for adding values

    3:  contacts.Add( new Contact('Bindesh', 'Vijayan'));

The collection initializer can work for all the types that meets the following criteria :

  • Implements IEnumerable interface
  • Has a public Add() method

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