Essential C++

6.7. Template Parameters as Strategy

Our LessThan class function object of Section 4.9 is a natural candidate for transforming into a template class:

template <typename elemType> 
class LessThan { 
public: 
   LessThan( const elemType &val ) : _val( val ){} 
   bool operator()( const elemType &val ) const 
                  { return val < _val; } 

   void val( const elemType &newval ) { _val = newval; } 
   elemType val() const { return _val; } 
private: 
   elemType _val; 
}; 

LessThan<int>    lti( 1024 ); 
LessThan<string> lts( "Pooh" ); 

A potential problem with this implementation is that it fails if the type supplied by the user does not define a less-than operator. One possible strategy is to provide a second template class with the comparison operator factored out of the class definition. ...