C＃中的命名空间

Question

namespace College
{
    namespace Lib
        {
            class Book
        {
            public void Issue()
            {
                // Implementation code
            }
        }
            class Journal
        {
            public void Issue()
            {
                // Implementation code
            }
        }
    }
}

Now to use Issue() method of class Book in a different namespace, the following two approaches work.

1. College.Lib.Book b = new College.Lib.Book(); b.Issue();

2. using College.Lib; Book b = new Book(); b.Issue();

And the following two approaches don't work.

i. using College; Lib.Book b = new Lib.Book(); b.Issue();

ii. using College.Lib.Book; Book b = new Book(); b.Issue();

Why don't the last two codes work?

Answer 1

In the first case, the original designers of C# decided that a using directive should bring the types in a namespace into scope, so to speak, but not bring the namespaces in a given namespace into scope. It was felt that "using" means "I have a bunch of types I want to use" and not "I have a bunch of sub-namespaces I want to use".

In the second case: the feature of "using" a type was added to C# 6. It brings the static members of the type "into scope". Perhaps you are using an older version of C#?