Chapter 75: C# 3.0 Features

Section 75.1: Implicitly typed variables (var)

The var keyword allows a programmer to implicitly type a variable at compile time. var declarations have the same type as explicitly declared variables.

var squaredNumber = 10 * 10;

var squaredNumberDouble = 10.0 * 10.0; var builder = new StringBuilder();

var anonymousObject = new

{

One = SquaredNumber,

Two = SquaredNumberDouble, Three = Builder

}

The types of the above variables are int, double, StringBuilder, and an anonymous type respectively.

It is important to note that a var variable is not dynamically typed. SquaredNumber = Builder is not valid since you are trying to set an int to an instance of StringBuilder

Section 75.2: Language Integrated Queries (LINQ)

//Example 1

int[] array = { 1, 5, 2, 10, 7 };

// Select squares of all odd numbers in the array sorted in descending order

IEnumerable<int> query = from x in array where x % 2 == 1 orderby x descending select x * x;

// Result: 49, 25, 1

Example from wikipedia article on C# 3.0, LINQ sub-section

Example 1 uses query syntax which was designed to look similar to SQL queries.

//Example 2

IEnumerable<int> query = array.Where(x => x % 2 == 1)

.OrderByDescending(x => x)

.Select(x => x * x);

// Result: 49, 25, 1 using 'array' as defined in previous example

Example from wikipedia article on C# 3.0, LINQ sub-section

Example 2 uses method syntax to achieve the same outcome as example 1.

It is important to note that, in C#, LINQ query syntax is syntactic sugar for LINQ method syntax. The compiler translates the queries into method calls at compile time. Some queries have to be expressed in method syntax. From MSDN - "For example, you must use a method call to express a query that retrieves the number of elements that match a specified condition."

could define properties like on code below.

var v = new { Amount = 108, Message = "Hello" };

It's also possible to create an array of anonymous types. See code below:

var a = new[] { new {

Fruit = "Apple", Color = "Red"

}, new {

Fruit = "Banana",

Color = "Yellow"

}

};

Or use it with LINQ queries:

var productQuery = from prod in products

select new { prod.Color, prod.Price };