//Description: The application goal of Hash function in programming is to map an object to an object through some transformation mechanism.

An integer value of type size _ t (that is, an unsigned long integer).

//Hash functions are mainly used in hash tables (widely used), passwords and other fields.

//Implementation description:

// (1), where function objects and generic technology are used, making it applicable to all types of objects (keywords).

// (2), commonly used types have corresponding specialization, such as string, char*, various shaping, etc.

// (3), the version is extensible. If there is a special demand for a certain type, specialization can be realized later.

// (4), the following implementation is generally placed in the header file, and any one containing it can use the hash function object.