ECMA-334: 10.5.3 Protected access for instance members

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10.5.3 Protected access for instance members

When a protected instance member is accessed outside the program text of the class in which it is declared, and when a protected internal instance member is accessed outside the program text of the program in which it is declared, the access is required to take place through an instance of the derived class type in which the access occurs. Let B be a base class that declares a protected instance member M, and let D be a class that derives from B. Within the class-body of D, access to M can take one of the following forms:

• An unqualified type-name or primary-expression of the form M.

• A primary-expression of the form E.M, provided the type of E is D or a class derived from D.

• A primary-expression of the form base.M.

In addition to these forms of access, a derived class can access a protected instance constructor of a base class in a constructor-initializer (§17.10.1).

[Example: In the following code

public class A
{
  protected int x;
  static void F(A a, B b)
  {
    a.x = 1; // Ok
    b.x = 1; // Ok
  }
}
public class B: A
{
  static void F(A a, B b)
  {
    a.x = 1; // Error, must access through instance of B
    b.x = 1; // Ok
  }
}

within A, it is possible to access x through instances of both A and B, since in either case the access takes place through an instance of A or a class derived from A. However, within B, it is not possible to access x through an instance of A, since A does not derive from B. end example]

In the context of generics (§25.1.6), the rules for accessing protected and protected internal instance members are augmented by the following:

• Within a generic class G, access to an inherited protected instance member M using a primary-expression of the form E.M is permitted if the type of E is a class type constructed from G or a class type derived from a class type constructed from G.