揭开函数适配器的面纱，编写自己的函数适配器-------小试牛刀

/*Just want to implement a function adapter*/ #include<iostream> #include<string> using std::string; using std::cout; using std::endl; template<class T> class GT{ public: typedef bool return_type ; //STL思想 typedef T arg_fir_type; typedef T arg_sec_type; public: bool operator()(T& opa,T& opb) { return opa == opb; } }; template<class T> //类实现函数适配器 class BindFirstArg{ public: BindFirstArg(T t,typename T::arg_fir_type f):pre(t),fir(f){} typename T::return_type operator()(typename T::arg_sec_type sec) { return pre(fir,sec); } private: T pre; //predicate typename T::arg_fir_type fir; }; //用工厂思想去除BindFirstArg<GT<string> >(GT<string>(),string("to")))调用时<GT<string> >冗余性。 template<class T,class Tp> inline BindFirstArg<T> bindFirstArg(T t,Tp f) { typedef typename T::arg_fir_type Arg_type; return BindFirstArg<T>(t,static_cast<Arg_type>(f)); } template<class InputInterator,class Pre> size_t count_if(InputInterator beg,InputInterator end,Pre func) { size_t count = 0; while(beg != end) { if(func(*beg++) != 0)count++; } return count; } int main() //三种调用方法 { string s[10] = {"I","want","to","implement","a","function","adapter","to","to","to"}; GT<string> g;BindFirstArg< GT<string> > b(g,string("I")); cout<<count_if(s,s+10,b)<<endl; cout<<count_if(s,s+10,BindFirstArg<GT<string> >(GT<string>(),string("to")))<<endl; cout<<count_if(s,s+10,bindFirstArg(g,string("to"))); }