模板推導提高程序效率，模板推導效率

模板推導提高程序效率，模板推導效率

STL 中有copy 函數， 感覺的效率還可以提高些， 就試著使用模板推導的方式決定調用不同的函數，本事就是根據形參類型的不同而調用不同的函數 ， 首先自定義最簡單的2個類 ，  true_type 和 false_type , 詳見如下代碼, VS2008驗證 OK 

// algorithm.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <vector>
#include <list>
namespace algor{
	struct true_type{};
	struct false_type{};
template <typename T>struct iterator_trait{
	typedef false_type value_type;
};

template <>struct iterator_trait<int*>{
	typedef true_type value_type;
};

template <>struct iterator_trait<char*>{
	typedef true_type value_type;
};

template <typename Iter1, typename Iter2>inline Iter2 t_copy(Iter1 first, Iter1 end, Iter2 out){
	typedef iterator_trait<Iter1>::value_type value_type;
	return copy_impl(first, end, out, has_trivial_assign<value_type>::value_type());
}
template <typename T>struct has_trivial_assign{
	typedef T value_type;
};



template <typename T>T* copy_impl(T* first, T* end, T* out, true_type){
	memmove(out, first, (end-first)*sizeof(T));
	return out + (end - first);
}
template <typename Iter1, typename Iter2>Iter2 copy_impl(Iter1 first, Iter1 end, Iter2 out, false_type){
	while(first != end)
	{
		*out = *first;
		++first;
		++out;
	}
	return out;
}
}
#define N 100000
struct MyFoo{
	char c;
	MyFoo& operator=(const MyFoo& f){

		c = f.c;
		return *this;
	}
};
using namespace std;
using namespace algor;
int _tmain(int argc, _TCHAR* argv[])
{
	MyFoo f;
	vector<MyFoo> vect(N, f);
	vector<MyFoo>::iterator first = vect.begin();
	vector<MyFoo>::iterator end = vect.end();

	list<MyFoo> t_list;
	t_list.resize(N);
	list<MyFoo>::iterator out = t_list.begin();
	int arr[N] = {1,};
	int brr[N] = {2,};
	int* aarr = arr;
	int* bbrr = brr;
	t_copy(aarr, aarr+N, bbrr);
	t_copy(first, end, out);
	return 0;
}