/** @brief Request the change in partition_vector capacity so that it
  *          can hold \a n elements. Throws the \a hpx::length_error
  *          exception.
  *  This function request partition_vector capacity should be at least
  *   enough to contain n elements. If n is greater than current
  *   partition_vector capacity, the function causes the partition_vector to
  *   reallocate its storage increasing its capacity to n (or greater).
  *  In other cases the partition_vector capacity does not got affected.
  *  It does not change the partition_vector size.
  * @param n minimum capacity of partition_vector
 void reserve(size_type n)
 void reserve(size_type const n) { data_.reserve(n); }