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Explicit Overrides (C++ Component Extensions)

This topic discusses how to explicitly override a member of a base class or interface. A named (explicit) override should only be used to override a method with a derived method that has a different name.

All Runtimes

Syntax

overriding-function-declarator = type::function [,type::function] { overriding-function-definition }
overriding-function-declarator = function { overriding-function-definition }

Parameters

  • overriding-function-declarator
    The return type, name, and argument list of the overriding function. Note that the overriding function does not have to have the same name as the function being overridden.

  • type
    The base type that contains a function to override.

  • function
    A comma-delimited list of one or more function names to override.

  • overriding-function-definition
    The function body statements that define the overriding function.

Remarks

Use explicit overrides to create an alias for a method signature, or to provide different implementations for methods witht the same signature.

For information about modifying the behavior of inherited types and inherited type members, see Override Specifiers (C++ Component Extensions).

Windows Runtime

Requirements

Compiler option: /ZW

Common Language Runtime

Remarks

For information about explicit overrides in native code or code compiled with /clr:oldSyntax, see Explicit Overrides (C++).

Requirements

Compiler option: /clr

Examples

Example

The following code example shows a simple, implicit override and implementation of a member in a base interface, not using explicit overrides.

// explicit_override_1.cpp
// compile with: /clr
interface struct I1 {
   virtual void f();
};

ref class X : public I1 {
public:
   virtual void f() {
      System::Console::WriteLine("X::f override of I1::f");
   }
};

int main() {
   I1 ^ MyI = gcnew X;
   MyI -> f();
}

Output

X::f override of I1::f

Example

The following code example shows how to implement all interface members with a common signature, using explicit override syntax.

// explicit_override_2.cpp
// compile with: /clr
interface struct I1 {
   virtual void f();
};

interface struct I2 {
   virtual void f();
};

ref struct X : public I1, I2 {
   virtual void f() = I1::f, I2::f {
      System::Console::WriteLine("X::f override of I1::f and I2::f");
   }
};

int main() {
   I1 ^ MyI = gcnew X;
   I2 ^ MyI2 = gcnew X;
   MyI -> f();
   MyI2 -> f();
}

Output

X::f override of I1::f and I2::fX::f override of I1::f and I2::f

Example

The following code example shows how a function override can have a different name from the function it is implementing.

// explicit_override_3.cpp
// compile with: /clr
interface struct I1 {
   virtual void f();
};

ref class X : public I1 {
public:
   virtual void g() = I1::f {
      System::Console::WriteLine("X::g");
   }
};

int main() {
   I1 ^ a = gcnew X;
   a->f();
}

Output

X::g

Example

The following code example shows an explicit interface implementation that implements a type safe collection.

// explicit_override_4.cpp
// compile with: /clr /LD
using namespace System;
ref class R : ICloneable {
   int X;

   virtual Object^ C() sealed = ICloneable::Clone {
      return this->Clone();
   }

public:
   R() : X(0) {}
   R(int x) : X(x) {}

   virtual R^ Clone() {
      R^ r = gcnew R;
      r->X = this->X;
      return r;
   }
};

See Also

Concepts

Component Extensions for Runtime Platforms