C++ Templates 第十六章模板与继承例子

[cpp]
#include

using namespace std;

// 中间模板
template
class Discrim : public Base
{
public:
Discrim() {
cout<<"Discrim()"< }

};

// 类Discrim 使的 PolicySelector 可以多次继承自相同的基类
template
class PolicySelector : public Discrim, public Discrim, public Discrim, public Discrim
{
};

class DefaultPol1 {
public:
void print() {
cout<<"p1 print()"< }
};

class DefaultPol2 {
public:
void print() {
cout<<"p2 print()"< }
};

class DefaultPol3 {
public:
void print() {
cout<<"p3 print()"< }
};

class DefaultPol4 {
public:
void print() {
cout<<"p4 print()"< }
};

// 建立一个缺省值的集合
class DefaultPols
{
public:
typedef DefaultPol1 dp1;
typedef DefaultPol2 dp2;
typedef DefaultPol3 dp3;
typedef DefaultPol4 dp4;
};

class DefaultPolArgs : virtual public DefaultPols {};

// 写几个模板覆盖缺省的policy参数
// 1
template
class Policy1_is : virtual public DefaultPols
{
public:
typedef Policy dp1;

virtual void print() {
dp1 dd;
dd.print();
}
};

// 2
template
class Policy2_is : virtual public DefaultPols
{
public:
typedef Policy dp2;

virtual void print() {
dp1 dd;
dd.print();
}
};

// 3
template

class Policy3_is : virtual public DefaultPols
{
public:
typedef Policy dp3;

Policy3_is() {
cout<<"Policy3_is()"< }

virtual void print() {
dp1 dd;
dd.print();
}
};

// 4
template
class Policy4_is : virtual public DefaultPols
{
public:
typedef Policy dp4;

virtual void print() {
dp1 dd;
dd.print();
}
};

// 这里所有的默认值相同
template typename PolicySet2 = DefaultPolArgs,
typename PolicySet3 = DefaultPolArgs,
typename PolicySet4 = DefaultPolArgs>
class BreadSlicer
{
public:
// 创建选择器，PolicySelector 在这里用模板参数分别初始化为对应的类型
// 这样就指定了 PolicySelector 的父类，从别从自个模板参数中继承而来。。。
// 这一块的理解还不是很清楚？？
typedef PolicySelector policies;

void print() {
typename policies::dp1 p1;
p1.print();

typename policies::dp2 p2;
p2.print();

typename policies::dp3 p3;
p3.print();

typename policies::dp4 p4;
p4.print();
}

};

class CustomPoliA
{
public:
void print() {
cout<<"CustomPoliA print()"< }

};

class CustomPoliB
{
public:
void print() {
cout<<"CustomPoliB print()"< }

};

int main(int argc, char **argv)
{
BreadSlicer, Policy4_is > bc;
bc.print();

return 0;
}

Starting: /home/robertkun/projects/tevent/build/tevent
p1 print()
p2 print()
CustomPoliA print()
CustomPoliB print()
*** Exited normally ***

C++ Templates 第十六章 模板与继承 例子