Question

What happens at runtime when number of namespaces are used in the program? Are the classes from the namespaces loaded entirely or the class used in program get loaded? What if there are unused namespaces present in the program?

Answer 1

Namespaces are really more of a compile time construct then a runtime construct. Putting classes into a namespace primarily only affects the name of the class. The “fully qualified name” of any class is actually its namespace hierarchy(separated by periods .) followed by the actual class name. You con’t “load” a namespace at runtime, the entire concept doesn’t exist.

When you compile a program, if you compile it to a library (.dll) you can add a reference to that .dll, in which case all of the classes in that dll are “accessibe” in your program. As for whether they’ll be loaded, it’s certainly possible for them to be loaded, but chances are due to lazy initialization unused classes won’t have a significant impact on performance.

When you add a using statement to the top of a file for a namespace, it doesn’t “load” that namespace. It will be used by the compiler to resolve all “unqualified” class names to “fully qualified” class names (at compile time). If you used just fully qualified class names in the first place you wouldn’t need any usings (but that really clutters up your code, so you should add them anyway).