Sample from an array without replacement.

sample.tcc

/* Sample from an array without replacement.
 *
 * \tparam T Array type.
 * \tparam arraySize Array size.
 *
 * \param a Array.
 *
 * \return Element of `a`.
 */
template <class T, size_t arraySize>
T sample(T (& a)[arraySize]) {
  thread_local size_t size {arraySize};

  size_t i {static_cast<size_t>(random(size))};

  T tmp {a[i]};
  a[i] = a[--size];
  a[size] = tmp;

  if (not size) {
    size = arraySize;
  }
  return tmp;
}