How to unroll a short loop in C++

Question

I wonder how to get something like this:

1. Write

   copy(a, b, 2, 3)
   

2. And then get

   a[2] = b[2];
   a[3] = b[3];
   a[4] = b[4];
   

I know that C #defines can't be used recursively to get that effect. But I'm using C++, so I suppose that template meta-programming might be appropriate.

I know there is a Boost library for that, but I only want that "simple" trick, and Boost is too "messy".

Answer 1

The most straightforward solution to this is to write a loop where the start and end values are known:

for(int i = 2; i <= 4; i++) {
  a[i]=b[i]; 
}

I think this is better than any sort of template/runtime-call mixture: The loop as written is completely clear to the compilers' optimizer, and there are no levels of function calls to dig through just to see what's going on.