filter.h

#ifndef HASH_FILTER_H_
#define HASH_FILTER_H_
#include <string>

namespace hard_core {
class FilterPolicy {
 public:
  virtual ~FilterPolicy() {}

  // Return the name of this policy.  Note that if the filter encoding
  // changes in an incompatible way, the name returned by this method
  // must be changed.  Otherwise, old incompatible filters may be
  // passed to methods of this type.
  virtual const char* Name() const = 0;

  // keys[0,n-1] contains a list of keys (potentially with duplicates)
  // that are ordered according to the user supplied comparator.
  // Append a filter that summarizes keys[0,n-1] to *dst.
  //
  // Warning: do not change the initial contents of *dst.  Instead,
  // append the newly constructed filter to *dst.
  virtual void CreateFilter(const std::string* keys, int n,
                            std::string* dst) = 0;

  // "filter" contains the data appended by a preceding call to
  // CreateFilter() on this class.  This method must return true if
  // the key was in the list of keys passed to CreateFilter().
  // This method may return true or false if the key was not on the
  // list, but it should aim to return false with a high probability.
  virtual bool KeyMayMatch(const std::string& key,
                           const std::string& filter) = 0;
};
}  // namespace hard_core

#endif