C++ named requirements: Hash (od C++11)
A Hash 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 T satisfies Hash if
- The type T satisfies FunctionObject, CopyConstructible, Destructible, and
Given
h
, a value of typeT
orconst T
, whose argument type isKey
k
, a value of type convertible toKey
orconst Key
u
, an lvalue expression of typeKey
Expression | Return type | Requirements |
---|---|---|
h(k) | std::size_t | the returned value depends only on the value of k for the duration of the program All evaluations of h(k) executed within a given execution of a program yield the same result for the same value of k. The probability of h(a)==h(b) for a!=b should approach 1.0/std::numeric_limits<std::size_t>::max(). |
h(u) | std::size_t | u is not modified |
Standard library
pub | hash(C++11) | hash function object |
Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR | Applied to | Behavior as published | Correct behavior |
---|---|---|---|
LWG 2291 | C++11 | same results for same arguments were required in all cases | only required within a single execution |