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ii.10.3.4-impact-of-overrides-on-derived-classes.md

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II.10.3.4 Impact of overrides on derived classes

When a method is overridden in a parent type, the override shall apply to the derived class according to the following:

  • If the derived class provides an implementation of a virtual method, then that method is not affected by any overrides of that method in the parent type

  • Otherwise, if the method is overridden in the parent type, the override is inherited, subject to any overrides in the derived class. [Note: This means that if the parent type overrides method A with method B, and the derived class does not provide an implementation or override of method A, but provides an overriding implementation of method B, then it is the derived class' implementation of B that will override method A in the derived class. It may be useful to think of this as virtual slot overriding. end Note.]

[Example: Consider the following (excerpted for clarity; all methods are declared public hidebysig virtual instance):

.class interface I
{
  .method newslot abstract void foo() {...}
}
.class A implements I
{
  .method newslot void foo() {...}
}
.class B extends A
{ 
 .method newslot void foo1() {.override I::foo ... }
}
.class C extends B
{
  .method void foo1() {...}
  .method void foo2() {.override A::foo ... }
}
.class D extends C
{
  .method newslot void foo() {...}
  .method void foo1(){...}
  .method void foo2(){...}
}

For this example, a sampling of the behavior of calls on objects of various types is presented in the following table:

Type of object Method invocation (callvirt) Method called Notes
B I::foo() B::foo1 Explicit override
C I::foo() C::foo1 Override of I::foo to virtual function foo1 is inherited from B
C A::foo() C::foo2 Explicit override
C B::foo1() C::foo1 Virtual override
D I::foo() D::foo1 Override of I::foo to virtual function foo1 is inherited
D A::foo() D::foo2 Explicit override of A::foo with virtual C::foo2 (D::foo doesn't override this because it is newslot)
D B::foo1() D::foo1 Virtual override
D C::foo1() D::foo1 Virtual override

end example]