ECMA-334: 10.7.1.2 Hiding through inheritance

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C# Language Specification

10. Basic concepts 10.7 Scopes 10.7.1 Name hiding 10.7.1.1 Hiding through nesting 10.7.1.2 Hiding through inheritance

© 2006 ECMA International

10.7.1.2 Hiding through inheritance

Name hiding through inheritance occurs when classes or structs redeclare names that were inherited from base classes. This type of name hiding takes one of the following forms:

• A constant, field, property, or event introduced in a class or struct hides all base class members with the same name and no type parameters.

• A type introduced in a class or struct hides all base class members with the same name and same number of type parameters.

• A method introduced in a class or struct hides all non-method base class members with the same name and either, the same number of type parameters or no type parameters, and all base class methods with the same signature.

• An indexer introduced in a class or struct hides all base class indexers with the same signature (parameter count and types).

Contrary to hiding a name from an outer scope, hiding an accessible name from an inherited scope causes a warning to be reported. [Example: In the following code

class Base
{
  public void F() {}
}
class Derived: Base
{
  public void F() {}  // Warning, hiding an inherited name
}

the declaration of F in Derived causes a warning to be reported. Hiding an inherited name is specifically not an error, since that would preclude separate evolution of base classes. For example, the above situation might have come about because a later version of Base introduced an F method that wasn’t present in an earlier version of the class. Had the above situation been an error, then any change made to a base class in a separately versioned class library could potentially cause derived classes to become invalid. end example]

The warning caused by hiding an inherited name can be eliminated through use of the new modifier: [Example:

class Base { public void F() {} } class Derived: Base { new public void F() {} }

The new modifier indicates that the F in Derived is "new", and that it is indeed intended to hide the inherited member. end example]

A declaration of a new member hides an inherited member only within the scope of the new member. [Example:

class Base
{
  public static void F() {}
}
class Derived: Base
{
  new private static void F() {} // Hides Base.F in Derived only
}
class MoreDerived: Derived
{
  static void G() { F(); }       // Invokes Base.F
}

In the example above, the declaration of F in Derived hides the F that was inherited from Base, but since the new F in Derived has private access, its scope does not extend to MoreDerived. Thus, the call F() in MoreDerived.G is valid and will invoke Base.F. end example]