c++ - 为什么带有花括号初始化器列表的构造函数/虚拟析构函数不起作用？

Question

为什么下面的代码不能编译？

#include <vector>

class Foo
{
public:
    Foo()
    { }

    virtual ~Foo()
    { }

    std::vector<int> aVec;
};


Foo bar =
{
    { 1, 2, 3, 4, 5 }
};

编译以下代码时:

#include <vector>

class Foo
{
public:

    /*Foo()
    { }

    virtual*/ ~Foo()
    { }

    std::vector<int> aVec;
};


Foo bar =
{
    { 1, 2, 3, 4, 5 }
};

除了提及语言规则外，请详细说明这些规则背后的基本原理。

为什么constructor和virtual destructor的存在会停止初始化？

Answer 1

因为 Foo 是类类型，所以大括号初始化列表被视为 aggregate initialization .除其他外，这要求该类没有显式构造函数或虚拟成员:

Aggregate initialization is a form of list-initialization, which initializes aggregates. An aggregate is one of the following types:

class type (typically, struct or union), that has...

• no private or protected non-static data members

• no user-provided, inherited, or explicit (since C++17) constructors (explicitly defaulted or deleted constructors are allowed)

• no virtual, private, or protected base classes
• no virtual member functions
• default member initializers