Overview of What's New in C# 3.0 C# 3.0 includes some great new features. Most of the new features are stepping stones designed to support Language Integrated Query (LINQ). Nevertheless, all of them are extremely useful when used individually outside of the context of LINQ. Many of them allow programmers to employ functional programming techniques more easily. C# now supports implicitly typed local variables by making use of a new keyword var. It's important to note that these variables are not typeless; rather, their type is inferred at compile time. You can read more about them in Chapter 3. Have you ever wanted to create a simple type to hold some related data but been annoyed at having to create an entire new class? In many cases, the new support for anonymous types helps relieve you of this burden. Using anonymous types, you can define and instantiate a type all in one compound statement. I cover anonymous types in Chapter 4. Auto-implemented properties are another helpful new feature to save us some typing and reduce the potential to introduce bugs. How many times have you simply declared a class to hold a few pieces of data and been annoyed with the amount of typing required to create property accessors for that data? After all, doing so follows good encapsulation practices. Thankfully, autoimplemented properties greatly reduce the amount of typing necessary to define properties on types. You can read more about them in Chapter 4. While we're on the subject of conveniences, C# 3.0 also introduces two new features that help when instantiating and initializing object instances. Using object and collection initializers, you can instantiate and initialize either an object or a collection in one compound statement. I cover object initializers in Chapter 4 and collection initializers in Chapter 9. C# 2.0 introduced partial class definitions to facilitate using code generators. C# 3.0 adds to that by introducing partial methods. Using partial methods, a code generator can declare a method signature, and the consumer of that generated code, the one that creates the rest of the partial class definition, can choose to implement it or not. You can read more about partial methods in Chapter 4. Extension methods are one of the most exciting new features. Taken from the surface view, they are merely static methods that can be called as if they were instance methods. They do not get any special access into the instance they are operating on, so in that respect, they are just like static methods. However, the syntax they foster allows us to program in a more functional manner, usually resulting in clearer and more readable code. I devote the entire Chapter 14 to extension methods and what you can do with them. Probably more compelling than extension methods is support for lambda expressions. Lambda expressions supersede support for anonymous methods. That is, if lambda expressions had existed in C# 2.0, there would have been no need for anonymous methods at all. However, lambda expressions offer much more than anonymous methods as they can be converted into both delegates and expression trees. Lambda expressions are covered in Chapter 15. The granddaddy of all new C# 3.0 features has to be LINQ, which builds upon all of the new features, especially extension methods, lambda expressions, and anonymous types. It also adds some new language keywords to allow us to code intuitive query statements, thus seamlessly bridging the gap between the object-oriented world and the data world. You can use LINQ to access data from multiple sources. Visual Studio provides the capability to use LINQ on native object collections, SQL data stores, and XML. Support for many other data sources is coming soon from both Microsoft and third parties. For example, you'll be able to use LINQ to connect to Windows Management Instrumentation (WMI), the Document Object Model (DOM), and the Web. Additionally, there are implementations in the works to use LINQ against popular web sites such as Google and Flickr. Chapter 16 is devoted to LINQ.