From d5970f8ed49a15d19265c71c8618e32a9534eeee Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@gmail.com>
Date: Fri, 3 Jan 2020 13:10:02 +0100
Subject: new_type: implement support for derivation of Hash

---
 doc/src/index.rst | 30 ++++++++++++++++++++++++++++++
 1 file changed, 30 insertions(+)

(limited to 'doc')

diff --git a/doc/src/index.rst b/doc/src/index.rst
index 07f5fc3..133ab7e 100644
--- a/doc/src/index.rst
+++ b/doc/src/index.rst
@@ -1,5 +1,9 @@
 .. cpp:namespace-push:: nt
 
+.. |BaseTypeDoc| replace:: The type of the contained object
+.. |TagTypeDoc| replace:: A tag to uniquely identify an instance of :cpp:class:`nt::new_type`
+.. |DerivationClauseDoc| replace:: A (possibly empty) list of derivation tags as generated by :cpp:func:`nt::deriving`
+
 .. only:: html
 
    .. contents:: Table of Contents
@@ -395,6 +399,26 @@ Arithmetic Operators
 
    **enablement:** This operator shall be available iff. a) :cpp:type:`new_type<BaseType, TagType, DerivationClause>::base_type` is divide-assignable using the operator :literal:`/=` and b) :cpp:type:`DerivationClause` includes :cpp:var:`Arithmetic`.
 
+:cpp:struct:`std::hash` Support
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+.. cpp:namespace-pop::
+
+.. cpp:struct:: template<typename BaseType, typename TagType, auto DerivationClause> \
+                std::hash<nt::new_type<BaseType, TagType, DerivationClause>>
+
+   :tparam BaseType: |BaseTypeDoc|
+   :tparam TagType: |TagTypeDoc|
+   :tparam DerivationClause: |DerivationClauseDoc|
+
+   .. cpp:function:: constexpr std::size operator()(nt::new_type<BaseType, TagType, DerivationClause> const &) const
+
+      **enablement:** This operator shall be available iff. a) :cpp:type:`nt::new_type::base_type` is hashable and b) :cpp:var:`DerivationClause` contains :cpp:var:`nt::Hash`.
+
+   .. versionadded:: 1.0.0
+
+.. cpp:namespace-push:: nt
+
 Header :literal:`<newtype/derivable.hpp>`
 =========================================
 
@@ -433,6 +457,12 @@ Standard derivation tags
 
    .. versionadded:: 1.0.0
 
+.. cpp:var:: auto constexpr Hash = derivable<struct hash_tag>{}
+
+   This tag enables the derivation of a specialization of :cpp:struct:`std::hash`
+
+   .. versionadded:: 1.0.0
+
 .. cpp:var:: auto constexpr Indirection = derivable<struct indirection_tag>{}
 
    This tag enables the derivation of the "member access through pointer" operators :cpp:func:`new_type::operator->`
-- 
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