问题描述
当一个方法在类中声明为 virtual 时，它在派生类中的覆盖自动被视为 virtual 在这种情况下，C ++语言使此关键字 virtual 可选：
When a method is declared as virtual in a class, its overrides in derived classes are automatically considered virtual as well, and the C++ language makes this keyword virtual optional in this case:
class Base {
virtual void f();
};
class Derived : public Base {
void f(); // 'virtual' is optional but implied.
};
我的问题是： virtual 可选？
我知道编译器不是绝对必要的，但我认为开发人员将受益，如果这样的约束被强制
I know that it is not absolutely necessary for the compiler to be told that, but I would think that developers would benefit if such a constraint was enforced by the compiler.
例如，当我阅读别人的代码时我不知道一个方法是否是虚拟的，我必须跟踪它的超类来确定。而一些编码标准（）使其成为必须将 virtual 关键字放在所有子类中。
E.g., sometimes when I read others' code I wonder if a method is virtual and I have to track down its superclasses to determine that. And some coding standards (Google) make it a 'must' to put the virtual keyword in all subclasses.
推荐答案
真的更好，使编译器强制执行虚拟在这种情况下，我同意这是一个错误设计，为维持向后兼容性。
Yeah, it would really be nicer to make the compiler enforce the virtual in this case, and I agree that this is a error in design that is maintained for backwards compatibility.
但是有一个技巧这将是不可能没有它：
However there's one trick that would be impossible without it:
class NonVirtualBase {
void func() {};
};
class VirtualBase {
virtual void func() = 0;
};
template<typename VirtualChoice>
class CompileTimeVirtualityChoice : public VirtualChoice {
void func() {}
};
我们有编译时选择，我们想要func的虚拟化：
With the above we have compile time choice wether we want virtuality of func or not:
CompileTimeVirtualityChoice<VirtualBase> -- func is virtual
CompileTimeVirtualityChoice<NonVirtualBase> -- func is not virtual
...但同意，这是一个次要的好处，一个函数的虚拟性和我自己，我总是试图在适当的地方类型虚拟。
... but agreed, it's a minor benefit for the cost of seeking a function's virtuality, and myself, I always try to type virtual everywhere where applicable.
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