| // Copyright (C) 2003 Davis E. King ([email protected]) | |
| // License: Boost Software License See LICENSE.txt for the full license. | |
| namespace dlib | |
| { | |
| // ---------------------------------------------------------------------------------------- | |
| // ---------------------------------------------------------------------------------------- | |
| // ----------------------- provide a general hashing function object ---------------------- | |
| // ---------------------------------------------------------------------------------------- | |
| // ---------------------------------------------------------------------------------------- | |
| template < | |
| typename T | |
| > | |
| class general_hash | |
| { | |
| public: | |
| inline unsigned long operator() ( | |
| const T& item | |
| ) const; | |
| }; | |
| /*! | |
| Note that the default behavior of general hash is to attempt to cast | |
| an object of type T to an unsigned long and use that as the hash. | |
| REQUIREMENTS ON general_hash | |
| - must have a default constructor | |
| - must be a function object which overloads operator() as follows: | |
| unsigned long operator()(const T& item) | |
| - must take item, compute a hash number and return it | |
| - must not throw | |
| - must define the hash in such a way that all equivalent objects have | |
| the same hash. where equivalent means the following: | |
| definition of equivalent: | |
| a is equivalent to b if | |
| a < b == false and | |
| b < a == false | |
| !*/ | |
| // --------------- | |
| template < | |
| typename T | |
| > | |
| unsigned long general_hash<T>:: | |
| operator() ( | |
| const T& item | |
| ) const | |
| { | |
| // hash any types that have a conversion to uint64 | |
| return hash(static_cast<uint64>(item)); | |
| } | |
| // --------------- | |
| // std::string hash | |
| template <> | |
| inline unsigned long general_hash<std::string>:: | |
| operator() ( | |
| const std::string& item | |
| ) const | |
| { | |
| return hash(item); | |
| } | |
| // ---------------------------------------------------------------------------------------- | |
| // ---------------------------------------------------------------------------------------- | |
| } | |