cpp/named req/Hash

A is a function object for which the output depends only on the input and has a very low probability of yielding the same output given different input values.

Requirements
The type satisfies  if


 * The type satisfies, , , and

Given
 * , a value of type or, whose argument type is
 * , a value of type convertible to or
 * , an lvalue expression of type

The following expressions must be valid and have their specified effects