110 lines
3.2 KiB
Markdown
110 lines
3.2 KiB
Markdown
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### 使用c++11开发一个轻量级的AOP库
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AOP把软件系统分为两个部分：核心关注点和横切关注点。业务处理的主要流程是核心关注点，与之关系不大的部分是横切关注点。横切关注点的一个特点是，他们经常发生在核心关注点的多处，而各处基本相似，比如权限认证、日志、事务处理
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```
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#pragma once
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#define HAS_MEMBER(member)\
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template<typename T, typename... Args>struct has_member_##member\
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{\
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private:\
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template<typename U> static auto Check(int) -> decltype(std::declval<U>().member(std::declval<Args>()...), std::true_type()); \
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template<typename U> static std::false_type Check(...);\
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public:\
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enum{value = std::is_same<decltype(Check<T>(0)), std::true_type>::value};\
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};\
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HAS_MEMBER(Foo)
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HAS_MEMBER(Before)
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HAS_MEMBER(After)
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#include <NonCopyable.hpp>
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template<typename Func, typename... Args>
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struct Aspect : NonCopyable
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{
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Aspect(Func&& f) : m_func(std::forward<Func>(f))
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{
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}
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template<typename T>
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typename std::enable_if<has_member_Before<T, Args...>::value&&has_member_After<T, Args...>::value>::type Invoke(Args&&... args, T&& aspect)
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{
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aspect.Before(std::forward<Args>(args)...);//核心逻辑之前的切面逻辑
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m_func(std::forward<Args>(args)...);//核心逻辑
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aspect.After(std::forward<Args>(args)...);//核心逻辑之后的切面逻辑
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}
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template<typename T>
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typename std::enable_if<has_member_Before<T, Args...>::value&&!has_member_After<T, Args...>::value>::type Invoke(Args&&... args, T&& aspect)
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{
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aspect.Before(std::forward<Args>(args)...);//核心逻辑之前的切面逻辑
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m_func(std::forward<Args>(args)...);//核心逻辑
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}
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template<typename T>
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typename std::enable_if<!has_member_Before<T, Args...>::value&&has_member_After<T, Args...>::value>::type Invoke(Args&&... args, T&& aspect)
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{
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m_func(std::forward<Args>(args)...);//核心逻辑
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aspect.After(std::forward<Args>(args)...);//核心逻辑之后的切面逻辑
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}
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template<typename Head, typename... Tail>
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void Invoke(Args&&... args, Head&&headAspect, Tail&&... tailAspect)
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{
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headAspect.Before(std::forward<Args>(args)...);
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Invoke(std::forward<Args>(args)..., std::forward<Tail>(tailAspect)...);
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headAspect.After(std::forward<Args>(args)...);
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}
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private:
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Func m_func; //被织入的函数
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};
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template<typename T> using identity_t = T;
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//AOP的辅助函数，简化调用
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template<typename... AP, typename... Args, typename Func>
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void Invoke(Func&&f, Args&&... args)
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{
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Aspect<Func, Args...> asp(std::forward<Func>(f));
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asp.Invoke(std::forward<Args>(args)..., identity_t<AP>()...);
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}
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/*TEST CODE
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struct TimeElapsedAspect
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{
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void Before(int i)
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{
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m_lastTime = m_t.elapsed();
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}
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void After(int i)
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{
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cout <<"time elapsed: "<< m_t.elapsed() - m_lastTime << endl;
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}
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private:
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double m_lastTime;
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Timer m_t;
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};
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struct LoggingAspect
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{
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void Before(int i)
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{
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std::cout <<"entering"<< std::endl;
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}
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void After(int i)
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{
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std::cout <<"leaving"<< std::endl;
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}
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};
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void foo(int a)
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{
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cout <<"real HT function: "<<a<< endl;
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}
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int main()
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{
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Invoke<LoggingAspect, TimeElapsedAspect>(&foo, 1); //织入方法
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cout <<"-----------------------"<< endl;
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Invoke<TimeElapsedAspect, LoggingAspect>(&foo, 1);
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return 0;
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}
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*/
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```
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