sample_probe_fn Interface

# `sample_probe_fn` Interface

A sample probe policy.

This class serves to show the interface a probe functor needs to support.

1. `sample_probe_fn.hpp`
2. Public Methods:
   1. Constructors, destructor, and related.
3. Protected Methods:
   1. Offset methods.

## Constructors, destructor, and related.

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).

## Offset methods.

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.