What’s New in C# 3.0?

With the release of Visual Studio 2008, Microsoft has updated the C# language to its latest version, 3.0. C# 3.0, contains several key language enhancements that support the recently-announced Language Integrated Query (LINQ) feature. This article, the first of a two-part series, will walk you through each of these new, time-saving language enhancements and provide a couple of code examples illustrating how to use them.

Implicit Typing
In the previous version of C#, all variables must be explicitly typed/declared. For example, suppose you want to declare a string variable. You’d do this:

string str = "Hello World";

In C# 3.0, this is not mandatory. You can use the new var keyword to implicitly declare a variable. Consider the following statements:

var str = "Hello world!";
var pt = this.Size;

Here, str is implicitly declared as a string variable, while pt is implicitly declared as a Size variable. The type of variable declared is based on the value with which it is initialized. This method of variable declaration is known as Implicit Typing. Note that implicitly-type variables must be initialized when they are declared. The following statement will not compile:

var str;  //---missing initializer---

Also notice that IntelliSense will automatically know the type of the variable declared, as you can see in the figure below:

You can also use implicit typing on arrays. For example, the following statement declares points to be an array containing two Point objects:

var points = new[] { new Point(1, 2), new Point(3, 4) };

When you use implicit typing on arrays, make sure all the members in the array are of the same type. The following won’t compile since its members are of different types—string and Boolean:

var arr = new[] { "hello", true, "world" };

Implicit typing is useful in cases where you do not know the exact type of data you’re manipulating and you need the compiler to determine for you. Do not confuse the Object type with implicit typing. Variables declared as Object types need to be casted during runtime and IntelliSense does not know this type during development time. On the other hand, implicitly-typed variables are statically typed during design time—hence, IntelliSense is able to provide detailed information about the type. In terms of performance, an implicitly typed variable is no different from a normal typed variable.

Automatic Properties

In object-oriented programming, it’s good practice not to expose your member variables as publicly accessible. Instead, wrap them using properties so that you can impose business rules on them. For example, Listing 1 shows the definition of the Contact class containing two properties—Name and YearofBirth

There are some conditions to check for when setting the YearofBirth property, while there are none for setting the Name property. In fact, most of the time, you probably wo’t have any rules for setting the properties. When this happens, defining the get and set statements is superfluous. In C# 3.0, properties that do’t need any rules can simply be defined using a feature known as automatic properties. The following is a rewrite of the Contact class using this feature:

public class Contact
{
    uint _YearofBirth;

    public string Name {get; set;}

    public uint YearofBirth
    {
        get { return _YearofBirth; }
        set
        {
            if (value >= 1900 && value <= 2008)
                _YearofBirth = value;
            else
                _YearofBirth = 0;
        }
    }
}