C++ Template Metaprogramming/

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Seeing Real-World Examples of Using Type Traits

Seeing Real-World Examples of Using Type Traits

Explore the practical use of type traits and their utilization by developers.

We'll cover the following...

In the previous lesson of the section, we explored the various type traits that the standard library provides. It’s difficult and unnecessary to find examples for each and every type trait. However, it’s worth showcasing some examples where multiple type traits can be used for solving a problem. We’ll do this next.

Implementing a copy algorithm

The first example problem we’ll take a look at is a possible implementation for the std::copy standard algorithm (from the <algorithm> header). Keep in mind that what we’ll see next is not the actual implementation but a possible one that helps us learn more about the use of type traits. The signature of this algorithm is as follows:

template<typename InputIt, typename OutputIt>
constexpr OutputIt copy(InputIt first, InputIt last, OutputIt d_first);
Signature of the copy function

As a note, this function is constexpr only in C++20, but we can discuss it in this context. It copies all the elements in the range [first, last) to another range that begins with d_first. There is also an overload that takes an execution policy, and there’s a version, std::copy_if, that copies all the elements that match a predicate. But these are not important for our example. A straightforward implementation of this function is the following:

template<typename InputIt, typename OutputIt>
constexpr OutputIt copy(InputIt first, InputIt last, OutputIt d_first)
{
   while (first != last)
   {
      *d_first++ = *first++;
   }
   return d_first;
}
Straightforward implementation of the copy function

However, there are cases when this implementation can be optimized by simply copying memory. However, there are some conditions that must be met for this purpose:

  • Both iterator types, InputIt and OutputIt, must be pointers.

  • Both template parameters, InputIt and OutputIt, must point ...