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# final specifier

From cppreference.com
< cpp‎ | language

Specifies that a virtual function can not be overridden in a derived class or that a class cannot be inherited from.

### [edit] Syntax

The identifier `final`, if used, appears immediately after the declarator in the syntax of a member function declaration or a member function definition.

declarator virt-specifier-seq(optional) pure-specifier(optional) | (1) |
declarator virt-specifier-seq(optional) function-body | (2) |
class-key attr(optional) class-head-name class-virt-specifier(optional) `:`base-specifier-list(optional) | (3) |

1) In a member function declaration, `final` may appear in virt-specifier-seq immediately after the declarator, and before the pure-specifier, if used.
2) In a member function definition, `final` may appear in virt-specifier-seq immediately after the declarator and just before function-body (which may begin with a member initializer list)
3) In a class definition, `final` may appear as class-virt-specifier immediately after the name of the class, just before the colon that begins the base-specifier-list, if used.

In the cases (1,2), virt-specifier-seq, if used, is either override or `final`, or `final override` or `override final`. In the case (3), the only allowed value of class-virt-specifier, if used, is `final`

### [edit] Explanation

When used in a virtual function declaration or definition, `final` ensures that the function is virtual and specifies that it may not be overridden by derived classes. The program is ill-formed (a compile-time error is generated) otherwise

When used in a class definition, `final` specifies that this class may not appear in the base-specifier-list of another class definition (in other words, cannot be derived from). The program is ill-formed (a compile-time error is generated) otherwise. `final` can also be used with a union definition, in which case it has no effect (other than on the outcome of std::is_final), since unions cannot be derived from)

final is an identifier with a special meaning when used in a member function declaration or class head. In other contexts it is not reserved and may be used to name objects and functions.

### [edit] Example

    struct A
    {
        virtual void foo() final; // A::foo is final
        void bar() final; // Error: non-virtual function cannot be final
    };

    struct B final : A // struct B is final
    {
        void foo(); // Error: foo cannot be overridden as it's final in A
    };

    struct C : B // Error: B is final
    {
    };

### [edit] See also

- override specifier (since C++11)

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