Jaa

C#: Why I cannot call protected method from derived class

  • Artikkeli

Someone posted a comment in the internal alias on protected member access. The question is that the following code does not compile with the error "cannot access protected member Class1.Foo()"

 public class Class1{    protected void Foo()    {    }}public class Class2 : Class1{    private void Test()    {        Class2 a = new Class2();        Class1 b = new Class2();        a.Foo();        b.Foo(); // Fails to compile    }}

The argument that this code should work is that since Class1 is the base class of Class2 the access should be allowed. Long back (in another life) I had seen the same issue in C++. This is what I replied to the question....

The same issue exists in C++ as well, I think similar rationale will exist for C#. The following C++ code won’t compile as well

 class Class1{protected:    void Foo ()    {    }};class Class2 : public Class1{public:    void Test ()    {        Class2* a = new Class2 ();        Class1* b = new Class2 ();        a->Foo();b->Foo();     }};

This is because b is pointer (or reference) to a base class. For all we know b could point to an object of any class derived from Class1. If this call was allowed then it would break encapsulation as you would get access to a method inside the derived class

Comments

  • Anonymous
    November 09, 2005
    The comment has been removed
  • Anonymous
    November 09, 2005
    The comment has been removed
  • Anonymous
    May 30, 2007
    At least in C++ this protection can be disabled with an appropriate change to Class2's source file. Yes, I have done so.
  • Anonymous
    June 06, 2012
    The comment has been removed