Chapter 8: C# 4.0 Features

Chapter Contents

1.	Evolution of C#

2.	Optional and Named Arguments

3.	Optional Arguments

4.	Named Arguments

5.	Using Named and Optional Arguments in LINQ Queries

6.	Dynamic Typing

7.	Using Dynamic Types in LINQ Queries

8.	COM-Interop and LINQ

9.	Adding a COM-Interop Reference

10.	Building the Microsoft Excel Row Iterator

11.

Summary

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C# is an evolving language. This chapter looks at the new features added into C# 4.0 that combine to improve code readability and extend your ability to leverage LINQ to Object queries over dynamic data sources. The examples in this chapter show how to improve the coding model for developers around reading data from various sources, including text files and how to combine data from a COM-Interop source into a LINQ to Objects query.

Evolution of C#

C# is still a relatively new language (circa 2000) and is benefiting from continuing investment by Microsoft's languages team. The C# language is an ECMA and ISO standard (ECMA is an acronym for European Computer Manufacturers Association, and although it changed its name to Ecma International in 1994, it kept the name Ecma for historical reasons1). The standard ECMA-334 and ISO/IEC 23270:2006 is freely available online at the Ecma International website2 and describes the language syntax and notation. However, Microsoft's additions to the language over several versions take some time to progress through the standards process, so Microsoft's release cycle lags.

Each version of C# has a number of new features and generally a major theme. The major themes have been generics and nullable types in C# 2.0, LINQ in C# 3.0, and dynamic types in C# 4.0. The major features added in each release are generally considered to be the following:

[lb] C# 2.0-Generics (framework support was added, and C# benefited from this); iterator pattern (the yield keyword); anonymous methods (the delegate keyword), nullable types, and the null coalescing operator (??).
[lb] C# 3.0-Anonymous types, extension methods, object initializers, collection initializers, implicitly typed local variables (var keyword), lambda expressions (=>), and the LINQ query expression pattern.
[lb] C# 4.0-Optional and Named Arguments, Dynamic typing (dynamic type), improved COM-Interop, and Contra and Co-Variance.

The new features in C# 3.0 that launched LINQ can be found in Chapter 2, "Introducing LINQ to Objects," and this chapter documents each of the major new features in C# 4.0 from the perspective of how they impact the LINQ story.