sealed (C++ Component Extensions)
The latest version of this topic can be found at sealed (C++ Component Extensions). sealed is a context-sensitive keyword for ref classes that indicates that a virtual member cannot be overridden, or that a type cannot be used as a base type.
Note
The ISO C++11 Standard language has the final keyword, which is supported in Visual Studio. Use final on standard classes, and sealed on ref classes.
All Runtimes
Syntax
ref class
identifier
sealed {...};
virtualreturn-typeidentifier() sealed {...};
Parameters
identifier
The name of the function or class.
return-type
The type that's returned by a function.
Remarks
In the first syntax example, a class is sealed. In the second example, a virtual function is sealed.
The sealed keyword is valid for native targets, and also for the Windows Runtime and the common language runtime (CLR). For more information, see Override Specifiers and Native Compilations.
You can detect at compile time whether a type is sealed by using the __is_sealed (``type``) type trait. For more information, see Compiler Support for Type Traits.
sealed is a context-sensitive keyword. For more information, see Context-Sensitive Keywords.
Windows Runtime
Requirements
Compiler option: /ZW
Common Language Runtime
(There are no remarks for this language feature that apply to only the common language runtime.)
Requirements
Compiler option: /clr
Examples
This following code example shows the effect of sealed on a virtual member.
// sealed_keyword.cpp
// compile with: /clr
interface struct I1 {
virtual void f();
virtual void g();
};
ref class X : I1 {
public:
virtual void f() {
System::Console::WriteLine("X::f override of I1::f");
}
virtual void g() sealed {
System::Console::WriteLine("X::f override of I1::g");
}
};
ref class Y : public X {
public:
virtual void f() override {
System::Console::WriteLine("Y::f override of I1::f");
}
/*
// the following override generates a compiler error
virtual void g() override {
System::Console::WriteLine("Y::g override of I1::g");
}
*/
};
int main() {
I1 ^ MyI = gcnew X;
MyI -> f();
MyI -> g();
I1 ^ MyI2 = gcnew Y;
MyI2 -> f();
}
Output
X::f override of I1::f
X::f override of I1::g
Y::f override of I1::f
The next code example shows how to mark a class as sealed.
// sealed_keyword_2.cpp
// compile with: /clr
interface struct I1 {
virtual void f();
};
ref class X sealed : I1 {
public:
virtual void f() override {}
};
ref class Y : public X { // C3246 base class X is sealed
public:
virtual void f() override {}
};