班级与公共班级

Question

What is the difference between:

namespace Library{
    class File{
        //code inside it
   }
}

and:

namespace Library{
   public class File{
       //code inside it
   }
}

So what will be the difference between public class and class ?

Answer 1

Without specifying public the class is implicitly internal . This means that the class is only visible inside the same assembly. When you specify public , the class is visible outside the assembly.

It is also allowed to specify the internal modifier explicitly:

internal class Foo {}

Answer 2

The former is equivalent to:

namespace Library{
    internal class File{
        //code inside it
   }
}

All visibilities default to the least visible possible - private for members of class es and struct s (methods, properties, fields, nested classes and nested enum s) and internal for direct members of namespace s, because they can't be private.

internal means other code in the same assembly can see it, but nothing else (barring friend assemblies and the use of reflection).

This makes sense for two reasons:

1. You should be consciously making things use the least visibility possible anyway, to strengthen your encapsulation.
2. If they defaulted to public you could accidentally make something public that should be private or internal. If you accidentally make something not visible enough, you get an obvious compile error and fix it. If you accidentally make something too visible you introduce a flaw to your code that won't be flagged as an error, and which will be a breaking change to fix later.

It's often considered better style to be explicit with your access modifiers, to be clearer in the code, just what is going on.

Answer 3

默认情况下，所有class es（以及所有类型）都是internal ，因此为了能够从外部访问它们（没有像InternalsVisibleToAttribute这样的东西），你必须明确public它们。