- 责任链模式将对象连成一条链,让每个对象都有机会处理请求,从而解耦了发送者和处理者。发送者不需要关心具体的处理者,只要把请求发送到链上即可。如果当前对象不能处理请求,则沿着链转发给下一个对象,直到请求被一个对象处理为止。对象应按照从特殊到普遍的顺序链接,即处理范围最小的应最先链接
#include <cstdint>
#include <iostream>
#include <memory>
#include <utility>
class Handler {
public:
virtual void Process(std::int32_t i) {
if (p_) {
p_->Process(i); // 分派给链中的下一对象
} else {
std::cout << i << "can't be processed\n"; // 未指定下一对象则处理失败
}
}
void SetNext(std::shared_ptr<Handler> p) { p_ = std::move(p); }
virtual ~Handler() = default;
private:
std::shared_ptr<Handler> p_;
};
class A : public Handler {
public:
void Process(std::int32_t i) override {
if (i < 10) {
std::cout << i << " processed by A\n";
} else {
Handler::Process(i); // 若不能处理则转发给链中下一对象
}
}
};
class B : public Handler {
public:
void Process(std::int32_t i) override {
if (i < 100) {
std::cout << i << " processed by B\n";
} else {
Handler::Process(i);
}
}
};
class C : public Handler {
public:
void Process(std::int32_t i) override {
if (i < 1000) {
std::cout << i << " processed by C\n";
} else {
Handler::Process(i);
}
}
};
int main() {
auto a = std::make_shared<A>();
auto b = std::make_shared<B>();
auto c = std::make_shared<C>();
a->SetNext(b);
b->SetNext(c);
a->Process(9); // 9 processed by A
a->Process(999); // 999 processed by C
a->Process(99); // 99 processed by B
a->Process(9999); // 9999 can't be processed
}