每个 "complete" 对象都是 "most-derived" 对象吗？

Question

[..] An object that is not a subobject of any other object is called a complete object [..].

考虑一下这段代码：

struct Base {};
struct Derived : Base {};
struct MostDerived : Derived {};

我无法理解标准引用中的措辞：

[object.intro]/6:

If a complete object, a member subobject, or an array element is of class type, its type is considered the most derived class [..] An object of a most derived class type or of a non-class type is called a most derived object.

根据我的理解，完整对象的类型是“最派生的”class 类型。到此为止，后面的写法我真的看不懂了。

根据问题 "What does the "most derived object" mean?" 我认为（如果我错了请纠正我），“最衍生”类型的对象 class 只有，与 MostDerived 一样，被称为“最派生”对象。这是真的吗？
如果我像这样创建了一个 Base 的对象：Base b_obj = Base()，对象 b_obj 是“最衍生”对象吗？
如果我像这样创建了一个 Derived 的对象：Derived d_obj = Derived()，对象 d_obj 是否也是“最派生”对象？
“最衍生”中的“衍生”一词是指该对象是MostDerived之类的class的对象，还是表示该对象没有class 里面有子对象？

Answer 1

对象不是 class。
对象是 class、数组或 built-in-type 的实例化。
子对象是 class 成员对象、数组元素或对象的基础 class。
派生对象（和 most-derived 对象）仅在 class 继承的上下文中才有意义。

void foo() {
    int i = 0; // complete object, but not most-derived (not class type)
}

class A {
   int i = 0; // non complete object, not most-derived
}

void bar() {
    A a; // complete object, but not derived, so can't be "most derived"
}

class B : A { }

void biz() {
   B b; // complete object, derived object, and most-derived object
}

Is every "complete" object is "most-derived" object

没有。 most-derived对象是most-derivedclass对象，most-derivedclass必须是class类型。对象可能是 class 类型，但也存在 non-class 类型的对象。

class-type 的每个完整对象都是 most-derived 对象，前提是 class 继承。
一个most-derived对象可能是一个子对象，所以你不能从most-derived推断对象的完整性（但是，你可以推断most-derived对象是class类型）。

So if I have created an object of Base like this: Base b_obj = Base(), Is the object b_obj is "most-derived" object?

是的。 b_obj 的 most-derived 对象是 Base 类型的对象。但是，这不一定是一个完整的对象，因为这可能是一个 class 成员定义。同样，完整不是 most-derived.

的同义词

Also if I have created an object of Derived like this: Derived d_obj = Derived(), Is the object d_obj is also a "most-derived" object?

是的。 d_obj 的 most-derived 对象是 Derived.

类型的对象

如果您创建的对象类型为 MostDerived:

MostDerived md;

它是一个 MostDerived
它是一个 Derived
它是一个 Base
如果不是成员子对象，则为完整对象
其most-derived对象的类型为MostDerived
它有一个 Derived 类型的子对象，既不是完整对象也不是 most-derived 对象
其Derived类型的子对象有一个Base类型的子对象，既不是完整对象也不是most-derived对象。

Answer 2

Per the question "What does the "most derived object" mean?" I think that (correct me if I am wrong), objects of type "most-derived" class only, like MostDerived, are called "most-derived" objects. Does this true?.

"最派生 class" 应该依赖于所考虑的对象。它不是 class 本身的属性。

if I have created an object of Base like this: Base b_obj = Base(), Is the object b_obj is "most-derived" object?

是的，b_obj 是一个变量，因此是一个完整的对象。一个完整的对象总是一个 most-derived 对象。

if I have created an object of Derived like this: Derived d_obj = Derived(), Is the object d_obj is also a "most-derived" object?

同上。

Is the word "derived" in "most-derived" mean that the object is an object of a class like MostDerived, or mean that the object has no class subobject in it?

"most-derived" 表示没有其他对象是其正在考虑的对象的基础 class 子对象。这又不是 classes 本身的属性，而是取决于 class 的具体实例。例如，如果一个 Derived 对象是用 new Derived 创建的，那么它包含一个 Base 基础 class 子对象，而这个子对象不是 most-derived 对象。但是 Derived 对象是 most-derived 对象，因为没有例如任何 MostDerived 对象，它是基础 class 子对象。

Is every "complete" object is "most-derived" object

是的，每个完整的对象都是一个 most-derived 对象。但反之则不然。例如

struct A {
    Base b;
};

A a;

a是一个A类型的对象，它本身也是一个most-derived对象和一个完整的对象，但是a.b也是一个most-derived对象，虽然不是一个完整的对象。

每个 "complete" 对象都是 "most-derived" 对象吗？

Is every "complete" object a "most-derived" object?

c++

class

object

language-lawyer