#include <iostream>
#include <string>
#include <vector>
#include <map>
#include <set>
using namespace std;
//part 1
class A {
private:
A() {};
public:
static A* GetInstance() {
return new A();
}
};
//part 2
class A {
friend class B;
private:
A() {};
};
class B: public A {
};
//part 3
class A {
friend class B;
private:
A() {};
};
class B: virtual public A {
};
//part 4: 奇異遞歸模板模式（curiously recurring template pattern，CRTP）
template <typename T>
class A {
friend T;
private:
A() {};
};
class B: virtual public A<B> {
};
//part 4.2:
//這種技術獲得了類似于虛函數(shù)的效果，并避免了動態(tài)多態(tài)的代價。也有人把CRTP稱為“模擬的動態(tài)綁定”
template <typename T>
struct counter
{
static int objects_created;
static int objects_alive;
counter()
{
++objects_created;
++objects_alive;
}
counter(const counter&)
{
++objects_created;
++objects_alive;
}
protected:
~counter() // objects should never be removed through pointers of this type
{
--objects_alive;
}
};
template <typename T> int counter<T>::objects_created( 0 );
template <typename T> int counter<T>::objects_alive( 0 );
class X : counter<X>
{
...
};
class Y : counter<Y>
{
...
};
//part 5
class A {
protected:
A() {};
};
class B: virtual A {
};
//part 6
class B final {
};
//validate
class C: public B {
};
int main(int argc, char* argv[]) {
B b;
C c;
return 0;
}