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Note

Understand that extension methods do not literally change the compiled code base! This technique only

adds members to a type within the context of the current application.

When you define extension methods, the first restriction is that they must be defined within a

static class (see Chapter 5), and therefore each extension method must also be declared with the

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static keyword. The second point is that all extension methods are marked as such by using the

this keyword as a modifier on the first (and only the first) parameter of the method in question. The

third point is that every extension method can be called either from the correct instance in memory

or 

statically via the defining static class! Sound strange? Let’s look at a full example to clarify matters.