Hello Boost, Suppose I have a boost::unordered_setstd::string. Now I want to find() a const char *, std::string, or even a string without zero termination (Google StringPiece). Converting these to std::string just to do a lookup is wasteful. Instead, I want to provide functors like: struct either_hash { size_t operator()(const std::string &str) const { return boost::hash_range(str.begin(), str.end()); } size_t operator()(const char *str) const { return boost::hash_range(str, str + std::strlen(str)); } }; This raises the question: what is either_hash::argument_type ? But it seems this is not used by boost::unordered_set . It should probably be std::string to match the underlying hash table. Would it make sense to change find() to template <class query_type> const_iterator find(const query_type& q) const ? For those familiar with Google StringPiece, one solution is using boost::unordered_set<StringPiece>, but then I have to keep the underlying strings somewhere outside the table. Further, a generalized find is useful in other cases, but this was the easiest to explain. Kenneth