code: func (s *Set) ContainsFunc(f func(interface{}) bool) bool {
  	s.RLock()
  	defer s.RUnlock()
  	for k := range s.m {
  		if f(k) {
  			return true
  		}
  	}
  	return false
  }
docs: // ContainsFunc iterates all the items in the set and passes
  // each to f. It returns true the first time a call to f returns
  // true and false if no call to f returns true.