Programming C# 4.0, 6th Edition

Chapter 18. Dynamic

Older versions of C# had trouble interacting with certain kinds of programs, especially those in the Microsoft Office family. You could get the job done, but before C# 4.0, it needed a lot of effort, and the results were ugly. The problem came down to a clash of philosophies: Office embraces a dynamic style, while C# used to lean heavily toward the static style. C# 4.0 now provides better support for the dynamic style, making it much easier to program Microsoft Office and similar systems from C#.

Static Versus Dynamic

What exactly is the difference between static and dynamic? The terminology is slightly confusing because C# has a keyword called static which is unrelated, so you’ll need to put your knowledge of that static to one side for now. When it comes to the dynamic/static distinction, something is dynamic if it is decided at runtime, whereas a static feature is determined at compile type. If that sounds rather abstract, it’s because the distinction can apply to lots of different things, including the choice of which method to call, the type of a variable or an expression, or the meaning of an operator.

Let’s look at some concrete examples. The compiler is able to work out quite a lot of things about code during compilation, even code as simple as Example 18-1.

Example 18-1. Simple code with various static features

var myString = Console.ReadLine();
var modifiedString = myString.Replace("color", "colour");

We’ve used the var keyword here, so we’ve not told the ...