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Importing Types That Define Extension Methods

When you partition a set of static classes containing extension methods in a unique namespace,

other namespaces in that assembly will make use of the standard C# using keyword to import not

only the static classes themselves, but also each of the supported extension methods. This is impor-

tant to remember, because if you do not explicitly import the correct namespace, the extension

methods are not available for that C# code file.

In effect, although it can appear on the surface that extension methods are global in nature,

they are in fact limited to the namespaces that define them or the namespaces that import them.

Thus, if we wrap the definitions of our static classes (MyExtensions, TesterUtilClass, and

CarExtensions) into a namespace named MyExtensionMethods as follows:

namespace MyExtensionMethods

{

static class MyExtensions

{

...

}

static class TesterUtilClass

{

...

}

static class CarExtensions

{

...

}

}

other namespaces in the project would need to explicitly import the MyExtensionMethods name-

space to gain the extension methods defined by these types. Therefore, the following is a compiler

error: