Using substring-views to seach a multi-map of strings

substringview.cpp

#include <map>
#include <string>
#include <algorithm>
#include <iostream>

class substrview
{
  std::string::const_iterator _from;
  std::string::const_iterator _to;
public:
  substrview(
      const std::string &s,
      const std::size_t from,
      const std::size_t to)
    : _from(s.begin()+from), _to(s.begin()+to)
  { }

  std::string::const_iterator begin() const
  { return _from; }

  std::string::const_iterator end() const
  { return _to; }
};

inline bool cmpL(
    const std::pair<std::string,int> &entry,
    const substrview                 &val)
{
  return std::lexicographical_compare
    (entry.first.begin(),entry.first.end(),val.begin(),val.end());
}

inline bool cmpU(
   const substrview                 &val,
   const std::pair<std::string,int> &entry)
{
  return std::lexicographical_compare
    (val.begin(),val.end(),entry.first.begin(),entry.first.end());
}

int main()
{
  std::multimap<std::string,int> map {
    { "hello" , 1 },
    { "world" , 2 },
    { "foo" , 3 },
    { "foobar" , 4 },
    { "foo" , 5 },
  };

  std::string query { "barfoo" };
  for (std::size_t i = 0 ; i < query.size() ; ++i) {
    substrview subquery { query,i,query.size() };
    auto found_from = std::lower_bound(begin(map),end(map),subquery,cmpL);
    auto found_to   = std::upper_bound(begin(map),end(map),subquery,cmpU);
    while (found_from != found_to) {
      std::cout << found_from->first << ", " << found_from->second << '\n';
      ++found_from;
    }
  }

  return 0;
}