[#intro]
= Introduction

:idprefix: intro_

`boost::hash` is an implementation of the https://en.wikipedia.org/wiki/Hash_function[hash function] object specified by the http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf[Draft Technical Report on C++ Library Extensions] (TR1). It is the default hash function for link:../../../unordered/index.html[Boost.Unordered], link:../../../intrusive/index.html[Boost.Intrusive]'s unordered associative containers, and link:../../../multi_index/index.html[Boost.MultiIndex]'s hash indicies and link:../../../bimap/index.html[Boost.Bimap]'s `unordered_set_of`.

As it is compliant with http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1836.pdf[TR1], it will work with:

* integers
* floats
* pointers
* strings

It also implements the extension proposed by Peter Dimov in issue 6.18 of the http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2005/n1837.pdf[Library Extension Technical Report Issues List] (page 63), this adds support for:

* arrays
* `std::pair`
* the standard containers.
* extending `boost::hash` for custom types.

NOTE: This hash function is designed to be used in containers based on the STL and is not suitable as a general purpose hash function. For more details see the <<rationale,rationale>>.