26. std::count_if and predicate object

• 
      class less_than {
      public:
          less_than( int t )
          : m_thresh( t )
          {
          }
  
          bool operator( )( int v )
          {
              return v < m_thresh;
          }
  
      private:
          int m_thresh;
      };//class less_than
  
      vector< int > v1;
      int x = 14;
      int count_less = std::count_if( v1.begin(), v1.end(), less_than( x ) );