C++ Primer, Fifth Edition

Class Template Specializations

In addition to specializing function templates, we can also specialize class templates. As an example, we’ll define a specialization of the library hash template that we can use to store Sales_data objects in an unordered container. By default, the unordered containers use hash<key_type> (§ 11.4, p. 444) to organize their elements. To use this default with our own data type, we must define a specialization of the hash template. A specialized hash class must define

• An overloaded call operator (§ 14.8, p. 571) that returns a size_t and takes an object of the container’s key type

• Two type members, result_type and argument_type, which are the return and argument types, respectively, of the call operator

• The default ...