16 апреля 2009, Ник

0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112

#include <iostream>

///////////////////////////////////////////////////////////////////////
// METHOD 1
///////////////////////////////////////////////////////////////////////
class Producer;
class Consumer 
{
private:
    bool wasUsed;
public:
    Consumer();
    void use( Producer *const producer );
};

class Producer 
{
private:
    bool wasUsed;
public:
    Producer(); 
    void use( Consumer *const consumer );
};

Consumer::Consumer(): wasUsed( false ) 
{
}

void Consumer::use( Producer *const producer )
{
    if ( wasUsed ) 
    {
        return;
    }
    wasUsed = true;
    std::cout << "use" << std::endl;
    producer->use( this );
}

Producer::Producer(): wasUsed( false ) 
{
}

void Producer::use( Consumer *const consumer )
{
    if ( wasUsed ) 
    {
        return;
    }
    wasUsed = true;
    std::cout << "use" << std::endl;
    consumer->use( this );
}

///////////////////////////////////////////////////////////////////////
// METHOD 2
///////////////////////////////////////////////////////////////////////
template < class U > class User {
private:
    bool wasUsed;
public:
    User(): wasUsed( false ) 
    {
    }

    template < class U > void use( U *const user ) 
    {
        if ( wasUsed ) 
        {
            return;
        }
        wasUsed = true;
        std::cout << "use" << std::endl;
        user->use( this );
    }
};

class NewProducer;
class NewConsumer: public User< NewProducer > 
{
};
class NewProducer: public User< NewConsumer >
{
};

int main() {
    Producer *producer = new Producer();
    Consumer *consumer = new Consumer();
    // Displays two messages "use": one from producer, one from consumer.
    producer->use( consumer );
    // Displays nothing, because everything has been already used
    consumer->use( producer );
    // Displays nothing, because everything has been already used
    producer->use( consumer );
    delete consumer;
    delete producer;

    std::cout << std::endl;

    NewProducer *newProducer = new NewProducer();
    NewConsumer *newConsumer = new NewConsumer();
    // Displays two messages "use": one from producer, one from consumer.
    newProducer->use( newConsumer );
    // Displays nothing, because everything has been already used
    newConsumer->use( newProducer );
    // Displays nothing, because everything has been already used
    newProducer->use( newConsumer );
    delete newConsumer;
    delete newProducer;

    char c;
    std::cin >> c;
}