meta program (1) swap_iter

开始学习模板元编程了

#include <iostream>#include <string>#include <vector>#include <list>#include "boost/assign/list_of.hpp"#include "boost/type_traits/is_const.hpp"#include "boost/type_traits/is_reference.hpp"#include "boost/type_traits/is_same.hpp"#include "boost/shared_ptr.hpp"namespace swap_test{template<bool use_swap> struct use_swap_impl;template<typename ForwardIterator1, typename ForwardIterator2>static void swap_iter(ForwardIterator1& i1, ForwardIterator2& i2){typedef std::iterator_traits<ForwardIterator1> trait1;typedef typename trait1::value_type v1;typedef typename trait1::reference r1;typedef std::iterator_traits<ForwardIterator2> trait2;typedef typename trait2::value_type v2;typedef typename trait2::reference r2;bool const use_swap = boost::is_same<v1, v2>::value && boost::is_reference<r1>::value&& boost::is_reference<r2>::value;//防止代理引用vector<bool>的迭代器，见mpl page30.use_swap_impl<use_swap>::to_do_swap(i1, i2);}template<>//两种类型是一样的，struct use_swap_impl<true>{template<typename ForwardIterator1, typename ForwardIterator2>static void to_do_swap(ForwardIterator1& i1, ForwardIterator2& i2){std::swap(*i1, *i2);}};template<>struct use_swap_impl<false>{template<typename ForwardIterator1, typename ForwardIterator2>static void to_do_swap(ForwardIterator1& i1, ForwardIterator2& i2){typename std::iterator_traits<ForwardIterator1>::value_typetmp = *i1;*i1 = *i2;*i2 = tmp;}};void fun(){std::list<std::string> list = boost::assign::list_of("123")("456");std::vector<std::string> vec = boost::assign::list_of("789")("013");swap_iter(list.begin(), vec.begin());std::cout << *(list.begin()) << " " << *(vec.begin()) << std::endl;boost::shared_ptr<int> t1(new int(18));boost::shared_ptr<float> t2(new float(20.0f));int *tt1 = t1.get();float *tt2 = t2.get();swap_tier(tt1, tt2);std::cout << *t1 << " " << *t2 << std::endl;}}