A sample probe policy.
This class serves to show the interface a probe functor needs to support.
| Method | Description | 
| sample_probe_fn () | Default constructor. Must be default constructible. | 
| sample_probe_fn (const sample_probe_fn &r_other) | Copy constructor. Must be copy constructible. | 
| inline void swap (sample_probe_fn &r_other) | Swaps content. Must be swappable (if there is such a word). | 
| Method | Description | 
| inline size_type
  operator()
  (const_key_reference r_key,
    size_type i) const | Returns the i-th offset from the hash value of some key r_key. size_type is the size type on which the functor operates. |