Kenneth Heafield escribió:
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)); } };
You'd also have to provide a polymorphic replacement for std::equal_tostd::string allowing interoperability between std::string's and const char *s.
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 ?
FWIW, Boost.MultiIndex hashed indices do have a notion of "compatible keys" allowing for such heterogeneous lookup operations: http://www.boost.org/libs/multi_index/doc/tutorial/indices.html#hash_lookup http://www.boost.org/libs/multi_index/doc/reference/hash_indices.html#lookup Joaquín M López Muñoz Telefónica, Investigación y Desarrollo