c＃是否具有类似于“子”名称空间的名称，或像Java中那样的程序包作用域？

Question

I don't understand why an explicit reference isn't required in this situation:

//SomeStaticClass.cs
namespace WhyDontINeedUsingStatement {

    public static class SomeStaticClass {
        public static string Thingy {
            get { return "Behold! A thingy!"; }
        }
    }

    public class SomeNonStaticClass {
        public void DoSomethingUseful() {
            var foo = 9; 
        }
    }
}

// /SomeNamespace/SomeBoringClass.cs
namespace WhyDontINeedUsingStatement.SomeNamespace {
    public class SomeBoringClass {
        public static void DoSomething() {
            var whatever = SomeStaticClass.Thingy;

            var blah = new SomeNonStaticClass();
            blah.DoSomethingUseful();            
        }
    }
}

Why doesn't this require a using WhyDontINeedUsingStatement at the top? Aren't these separate namespaces, even though they start with the same thing?

I get that C# namespaces aren't quite the same thing as Java packages (and don't affect access control), but not why the second class is able to reference stuff from the first.

Answer 1

According to C# Language Specification Version 5.0, Section 9.2, it seems like using the . in a namespace declaration is syntactic sugar :

The qualified-identifier of a namespace-declaration may be a single identifier or a sequence of identifiers separated by “.” tokens. The latter form permits a program to define a nested namespace without lexically nesting several namespace declarations. For example,

namespace N1.N2
{
    class A {}
    class B {}
}

is semantically equivalent to

namespace N1
{
    namespace N2
    {
        class A {}
        class B {}
    }
}

So from inside of N2 you can see N1 , hence why you can use it.