将大括号内的“ this”传递给C ++中的类的对象

Question

class District
    :public State<District>
{
public:
    typedef Citizen Man;
    using State<District>::State;
    void CheckTransition( Man& Man );
private:
    int counter = 0;
};

class Citizen
    :public TopState<Citizen>
{
public:
    Citizen();
    District object{this};                 
};

I am unable to understand the usage of the last line in this piece. Can some one please explain what is happening here?

Line: District object{this};

I would like to understand the usage of this in this context within the braces to an object of a class.

Answer 1

Line: District object{this};
I would like to understand the usage of 'this' in this context within the braces to an object of a class.

A new way of initialization called brace-initialization was introduced in C++11 which makes the following possible:

int z{ 0 }; 
std::vector<int> v{ 1, 3, 5 }; 
Widget w1{10}; 
Widget w2{w1}; 

And it is also possible to use this for initialization.

From the standard 12.6.2/7 "Initializing bases and members" available here :

12.6.2 Initializing bases and members [class.base.init]
....
7 Names in the expression-list of a mem-initializer are evaluated in the scope of the constructor for which the mem-initializer is specified.
[Example:

class X {
     int a;
     int b;
     int i;
     int j;
public:
     const int& r;
     X(int i): r(a), b(i), i(i), j(this->i) {}
};

initializes X::r to refer to X::a , initializes X::b with the value of the constructor parameter i, initializes X::i with the value of the constructor parameter i , and initializes X::j with the value of X::i ; this takes place each time an object of class X is created. ]
[Note: because the mem-initializer are evaluated in the scope of the constructor, the this pointer can be used in the expression-list of a mem-initializer to refer to the object being initialized . ]

It's safe to use this pointer in initialization-list as long as it's not being used to access uninitialized members or virtual functions.