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用以指定一个 virtual function 不能被派生类重写#xff1b;或者指定一个 class 不能被继承#xff1b;2. 语法
对于类中成员函数有两种情况#xff1a;
只声明时#xff0c;final 紧跟参数的右括号#xff0c;如果是纯虚函数或者指定一个 class 不能被继承2. 语法
对于类中成员函数有两种情况
只声明时final 紧跟参数的右括号如果是纯虚函数final 会出现在 0 之前类中定义时final 在 函数体之前对于类定义final 紧跟类名
从c14 开始会引入一个 is_final 的判断确认一个 class 是否被定义为 final通过使用
std::is_finalA::value
来判断 class A 是否为 final。 3. 举例
struct A;
struct A final {}; // OK, definition of struct A,// not value-initialization of variable finalstruct X
{struct C { constexpr operator int() { return 5; } };struct B final : C{}; // OK, definition of nested class B,// not declaration of a bit-field member final
};// Abnormal final usage.struct final final // OK, definition of a struct named final from which
{ // you cannot inherit
};// struct final final {}; // Error: redefinition of struct final, NOT a// definition of a variable final using an elaborated// type specifier struct final followed by an// aggregate initialization// struct override : final {}; // Error: cannot derive from final base type;// override in given context is a normal name
void foo()
{[[maybe_unused]]final final; // OK, declaration of a variable named final of type// struct final
}struct final final; // OK, declaration of a variable named final of type// struct final using an elaborated type specifier
int main()
{
}final 只是一个标识在使用成员函数和类定义时有特殊的意义。而在其他情况下可以作为一个对象名、函数名、类名使用。 struct Base
{virtual void foo();
};struct A : Base
{void foo() final; // Base::foo is overridden and A::foo is the final overridevoid bar() final; // Error: bar cannot be final as it is non-virtual
};struct B final : A // struct B is final
{void foo() override; // Error: foo cannot be overridden as it is final in A
};struct C : B {}; // Error: B is final
注意这里的几个注意点
A 类中 foo() 继承自 Base 类并把自身定义为 final即后续继承A 的子类无法再重写 foo()A 类中 bar() 使用了final但 final 是用在 virtual 的成员函数B 类想重写 foo()是不允许的因为在A类中已经声明为 finalB 类定义的时候已经被声明为 final所以无法再被其他类继承即B 类不会有子类4. 原文摘录 Specifies that a virtual function cannot be overridden in a derived class or that a class cannot be derived from. When applied to a member function, the identifier final appears immediately after the declarator in the syntax of a member function declaration or a member function definition inside a class definition. When applied to a class, the identifier final appears at the beginning of the class definition, immediately after the name of the class. 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 inside a class definition, final may appear in virt-specifier-seq immediately after the declarator and just before function-body. 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-clause, 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 When used in a virtual function declaration or definition, final specifier 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 otherwise (a compile-time error is generated). 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 C14), 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.
