Difference between revisions of "cpp/language/final"
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@1@ In a member function declaration, {{tt|final}} may appear in {{spar|virt-specifier-seq}} immediately after the declarator, and before the {{rlp|abstract_class|pure-specifier}}, if used. | @1@ In a member function declaration, {{tt|final}} may appear in {{spar|virt-specifier-seq}} immediately after the declarator, and before the {{rlp|abstract_class|pure-specifier}}, if used. | ||
@2@ In a member function definition, {{tt|final}} may appear in {{spar|virt-specifier-seq}} immediately after the declarator and just before {{spar|function-body}} (which may begin with a {{rlp|initializer list|member initializer list}}) | @2@ In a member function definition, {{tt|final}} may appear in {{spar|virt-specifier-seq}} immediately after the declarator and just before {{spar|function-body}} (which may begin with a {{rlp|initializer list|member initializer list}}) | ||
| − | @3@ In a class definition, {{tt|final}} may appear immediately after the name of the class, just before the colon that begins the {{spar|base-specifier-list}}, if used. | + | @3@ In a class definition, {{tt|final}} may appear as {{spar|class-virt-specifier}} immediately after the name of the class, just before the colon that begins the {{spar|base-specifier-list}}, if used. |
| − | In the cases (1,2), {{spar|virt-specifier-seq}}, if used, is either {{rlp|override}} or {{tt|final}}, or {{tt|final override}} or {{tt|override final}}. | + | In the cases (1,2), {{spar|virt-specifier-seq}}, if used, is either {{rlp|override}} or {{tt|final}}, or {{tt|final override}} or {{tt|override final}}. In the case (3), the only allowed value of {{spar|class-virt-specifier}}, if used, is {{tt|final}} |
===Explanation=== | ===Explanation=== | ||
Revision as of 08:06, 7 February 2014
Specifies that a virtual function can not be overridden in a derived class or that a class cannot be inherited from.
Contents |
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)
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(3) | ||||||||
final may appear in virt-specifier-seq immediately after the declarator, and before the pure-specifier, if used.final may appear in virt-specifier-seq immediately after the declarator and just before function-body (which may begin with a member initializer list)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
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 compiler 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). he program is ill-formed (a compiler error is generated) otherwise.
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.
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 { };
See also
- override specifier (since C++11)
