[identity_view] Added boost::fusion::identity_view

doc/fusion.qbk

@@ -130,6 +130,7 @@
 [def __reverse_view__           [link fusion.view.reverse_view `reverse_view`]]
 [def __zip_view__               [link fusion.view.zip_view `zip_view`]]
 [def __flatten_view__           [link fusion.view.flatten_view `flatten_view`]]
+[def __identity_view__          [link fusion.view.identity_view `identity_view`]]
 
 [def __array__                  [link fusion.adapted.array array]]
 [def __std_pair__               [link fusion.adapted.std__pair `std::pair`]]

doc/html/index.html

@@ -163,6 +163,7 @@
 <dt><span class="section"><a href="fusion/view/zip_view.html">zip_view</a></span></dt>
 <dt><span class="section"><a href="fusion/view/transform_view.html">transform_view</a></span></dt>
 <dt><span class="section"><a href="fusion/view/reverse_view.html">reverse_view</a></span></dt>
+<dt><span class="section"><a href="fusion/view/identity_view.html">identity_view</a></span></dt>
 <dt><span class="section"><a href="fusion/view/nview.html">nview</a></span></dt>
 <dt><span class="section"><a href="fusion/view/repetitive_view.html">repetitive_view</a></span></dt>
 <dt><span class="section"><a href="fusion/view/flatten_view.html">flatten_view</a></span></dt>

doc/organization.qbk

@@ -60,6 +60,7 @@ link against.
     * single_view
     * transform_view
     * zip_view
+    * identity_view
 * container
     * deque
     * list

doc/sequence.qbk

@@ -133,6 +133,7 @@ For any Forward Sequence s the following invariants always hold:
 * __transform_view__
 * __reverse_view__
 * __zip_view__
+* __identity_view__
 
 [endsect]
 
@@ -201,6 +202,7 @@ are not defined in __forward_sequence__.
 * __iterator_range__ (where adapted sequence is a Bidirectional Sequence)
 * __transform_view__ (where adapted sequence is a Bidirectional Sequence)
 * __zip_view__       (where adapted sequences are models of Bidirectional Sequence)
+* __identity_view__  (where adapted sequence is a Bidirectional Sequence)
 
 [endsect]
 
@@ -289,6 +291,7 @@ are not defined in __bidirectional_sequence__.
 * __iterator_range__ (where adapted sequence is a Random Access Sequence)
 * __transform_view__ (where adapted sequence is a Random Access Sequence)
 * __zip_view__       (where adapted sequences are models of Random Access Sequence)
+* __identity_view__  (where adapted sequence is a Random Access Sequence)
 
 [endsect]
 
@@ -361,6 +364,7 @@ you can use `__result_of_value_at_key__<S, K>`.]
 * __joint_view__     (where adapted sequences are __associative_sequence__\ s and __forward_sequence__\ s)
 * __reverse_view__   (where adapted sequence is an __associative_sequence__ and a __bidirectional_sequence__)
 * __transform_view__ (where adapted sequence is an __associative_sequence__ and a __forward_sequence__)
+* __identity_view__  (where adapted sequence is an __associative_sequence__ and a __forward_sequence__)
 
 [endsect]
 

doc/view.qbk

@@ -1,6 +1,7 @@
 [/==============================================================================
     Copyright (C) 2001-2011 Joel de Guzman
     Copyright (C) 2006 Dan Marsden
+    Copyright (c) 2022 Denis Mikhailov
 
     Use, modification and distribution is subject to the Boost Software
     License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at
@@ -664,4 +665,60 @@ defined in __forward_sequence__.
 
 [endsect]
 
+[section identity_view]
+
+[heading Description]
+
+`identity_view` presents underlying sequence unchanged.
+
+[heading Header]
+
+    #include <boost/fusion/view/identity_view.hpp>
+    #include <boost/fusion/include/identity_view.hpp>
+
+[heading Synopsis]
+
+    template <typename Sequence>
+    struct identity_view;
+
+[heading Template parameters]
+
+[table
+    [[Parameter]            [Description]                   [Default]]
+    [[`Sequence`]           [A __forward_sequence__]        []]
+]
+
+[heading Model of]
+
+* A model of __forward_sequence__ if `Sequence` is a __forward_sequence__ else, __bidirectional_sequence__ if `Sequence` is a __bidirectional_sequence__
+else, __random_access_sequence__ if `Sequence` is a __random_access_sequence__.
+* __associative_sequence__ if `Sequence` implements the __associative_sequence__ model.
+
+[variablelist Notation
+    [[`IV`]             [An `identity_view` type]]
+    [[`s`]              [An instance of `Sequence`]]
+    [[`iv`, `iv2`]      [Instances of `identity_view`]]
+]
+
+[heading Expression Semantics]
+
+Semantics of an expression is defined only where it differs from, or is not
+defined in the implemented models.
+
+[table
+    [[Expression]           [Semantics]]
+    [[`IV(s)`]              [Creates an `identity_view` given sequence, `s`.]]
+    [[`IV(iv)`]             [Copy constructs an `identity_view` from another `identity_view`, `iv`.]]
+    [[`iv = iv2`]           [Assigns to an `identity_view`, `iv`, from another `identity_view`, `iv2`.]]
+]
+
+[heading Example]
+    typedef __vector__<int, short, double> vector_type;
+    vector_type vec(2, 5, 3.3);
+
+    __identity_view__<vector_type> identity(vec);
+    std::cout << identity << std::endl; // (2 5 3.3)
+
+[endsect]
+
 [endsect]