C ++ metaprogramming模板与内联 [英] C++ metaprogramming with templates versus inlining

问题描述

是否有必要编写如下代码来复制数组元素：

Is it worth to write code like the following to copy array elements:

#include <iostream>
using namespace std;


template<int START, int N> 
struct Repeat { 
  static void copy (int * x, int * y) {
   x[START+N-1] = y[START+N-1];
   Repeat<START, N-1>::copy(x,y);
  }
};

template<int START> 
struct Repeat<START, 0> { 
  static void copy (int * x, int * y) {
   x[START] = y[START];
  }
};



int main () {


   int a[10];
   int b[10];

             // initialize
   for (int i=0; i<=9; i++) {
     b[i] = 113 + i;
     a[i] = 0;
   }

            // do the copy (starting at 2, 4 elements)
  Repeat<2,4>::copy(a,b);

             // show
   for (int i=0; i<=9; i++) {
   cout << a[i] << endl;
   }

} // () 

更好地使用内联函数？

第一个缺点是你不能在模板中使用变量。

A first drawback is that you can't use variables in the template.

推荐答案

这不是更好。首先，它不是真正的编译时间，因为你在这里进行函数调用。如果你很幸运，编译器会内联这些，最后是一个循环，你可以用更少的代码写自己（或只是使用 std :: copy ）

That's not better. First of all, it's not really compile time, since you make function calls here. If you are lucky, the compiler will inline these and end up with a loop you could have written yourself with much less amount of code (or just by using std::copy).

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