Implementing Copy Algorithm

Implementing your own version of std::ranges::copy() can be a great exercise to understand how the algorithm works.

The basic idea is to iterate over the source range and copy each element to the destination range. Here’s a simplified implementation:

1#include <iostream>
2#include <vector>
3
4template <typename InputIt, typename OutputIt>
5OutputIt my_copy(InputIt first,
6  InputIt last, OutputIt d_first) {
7  while (first != last) {
8    *d_first++ = *first++; 
9  }
10  return d_first;
11}
12
13int main() {
14  std::vector<int> Source{1, 2, 3, 4, 5};
15  std::vector<int> Destination(5);
16
17  my_copy(Source.begin(), Source.end(),
18    Destination.begin()); 
19
20  for (int Value : Destination) {
21    std::cout << Value << ", ";
22  }
23}

11, 2, 3, 4, 5,

In this implementation:

• my_copy() takes three parameters: the beginning and end of the source range, and the beginning of the destination range.
• It uses a while loop to iterate from first to last, copying each element to the destination.

For more advanced functionality similar to std::ranges::copy(), you can add iterator traits to ensure compatibility with a wider range of iterator types. Here’s an enhanced version using iterator traits:

1#include <iostream>
2#include <vector>
3#include <iterator>
4#include <type_traits>
5
6template <typename InputIt, typename OutputIt>
7OutputIt my_copy(
8  InputIt first, InputIt last, OutputIt d_first) {
9  using ValueType =
10    typename std::iterator_traits<InputIt>::value_type;
11
12  static_assert(
13    std::is_copy_assignable<ValueType>::value,
14    "Value type must be copy assignable"
15  );
16
17  while (first != last) {
18    *d_first++ = *first++; 
19  }
20  return d_first;
21}
22
23int main() {
24  std::vector<int> Source{1, 2, 3, 4, 5};
25  std::vector<int> Destination(5);
26
27  my_copy(Source.begin(), Source.end(),
28    Destination.begin()); 
29
30  for (int Value : Destination) {
31    std::cout << Value << ", ";
32  }
33}

11, 2, 3, 4, 5,

In this version:

• std::iterator_traits is used to ensure the input iterator's value type is copy assignable.
• This makes my_copy() more robust and similar to the standard library's approach.

Implementing your own copy algorithm helps you understand the intricacies of range-based algorithms and iterator concepts in C++.