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a little progress with indirect iterator

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[SVN r21294]
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Jeremy Siek
2003-12-16 22:15:48 +00:00
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@ -3,203 +3,12 @@
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<title>Iterator Facade and Adaptor</title>
<meta name="author" content="David Abrahams, Jeremy Siek, Thomas Witt" />
<meta name="organization" content="Boost Consulting, Indiana University Open Systems Lab, University of Hanover Institute for Transport Railway Operation and Construction" />
<meta name="date" content="2003-11-24" />
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<div class="document" id="iterator-facade-and-adaptor">
@ -510,7 +319,7 @@ of the derived iterator type. These member functions are described
briefly below and in more detail in the iterator facade
requirements.</p>
<blockquote>
<table border class="table">
<table class="table" frame="border" rules="all">
<colgroup>
<col width="44%" />
<col width="56%" />
@ -903,7 +712,7 @@ object of type <tt class="literal"><span class="pre">X</span></tt>, <tt class="l
object of a single pass iterator type interoperable with <tt class="literal"><span class="pre">X</span></tt>, and <tt class="literal"><span class="pre">z</span></tt>
is a constant object of a random access traversal iterator type
interoperable with <tt class="literal"><span class="pre">X</span></tt>.</p>
<table border class="table">
<table class="table" frame="border" rules="all">
<colgroup>
<col width="19%" />
<col width="21%" />
@ -1442,25 +1251,32 @@ iterators over smart pointers, which the impl handles. -JGS -->
template &lt;
class Iterator
, class Value = use_default
, unsigned Access = use_default_access
, class Traversal = use_default
, class CategoryOrTraversal = use_default
, class Reference = use_default
, class Difference = use_default
&gt;
class indirect_iterator
: public iterator_adaptor&lt;/* see discussion */&gt;
: public iterator_adaptor&lt;
indirect_iterator&lt;Iterator, Value, Access, Traversal,
Reference, Difference&gt;,
Iterator,
/* Value = see below */,
CategoryOrTraversal,
Reference,
Difference&gt;
{
friend class iterator_core_access;
public:
indirect_iterator();
indirect_iterator(Iterator x);
template &lt;
class Iterator2, class Value2, unsigned Access2, class Traversal2
class Iterator2, class Value2, class Category2
, class Reference2, class Difference2
&gt;
indirect_iterator(
indirect_iterator&lt;
Iterator2, Value2, Access2, Traversal2, Reference2, Difference2
Iterator2, Value2, Category2, Reference2, Difference2
&gt; const&amp; y
, typename enable_if_convertible&lt;Iterator2, Iterator&gt;::type* = 0 // exposition
);
@ -1474,29 +1290,27 @@ private: // as-if specification
</div>
<div class="section" id="indirect-iterator-requirements">
<h4><a class="toc-backref" href="#id42" name="indirect-iterator-requirements"><tt class="literal"><span class="pre">indirect_iterator</span></tt> requirements</a></h4>
<p>The <tt class="literal"><span class="pre">value_type</span></tt> of the <tt class="literal"><span class="pre">Iterator</span></tt> template parameter should
itself be dereferenceable. The return type of the <tt class="literal"><span class="pre">operator*</span></tt> for
the <tt class="literal"><span class="pre">value_type</span></tt> must be the same type as the <tt class="literal"><span class="pre">Reference</span></tt> template
parameter. The <tt class="literal"><span class="pre">Value</span></tt> template parameter will be the <tt class="literal"><span class="pre">value_type</span></tt>
for the <tt class="literal"><span class="pre">indirect_iterator</span></tt>, unless <tt class="literal"><span class="pre">Value</span></tt> is const. If <tt class="literal"><span class="pre">Value</span></tt>
is <tt class="literal"><span class="pre">const</span> <span class="pre">X</span></tt>, then <tt class="literal"><span class="pre">value_type</span></tt> will be <em>non-</em> <tt class="literal"><span class="pre">const</span> <span class="pre">X</span></tt>. The
default for <tt class="literal"><span class="pre">Value</span></tt> is</p>
<p>The following requirements are placed on the type
<tt class="literal"><span class="pre">iterator_traits&lt;Iterator&gt;::value_type</span></tt>. Let <tt class="literal"><span class="pre">i</span></tt> be an object of
type <tt class="literal"><span class="pre">iterator_traits&lt;Iterator&gt;::value_type</span></tt>. Then <tt class="literal"><span class="pre">*i</span></tt> must be a
valid expression, and the type of <tt class="literal"><span class="pre">*i</span></tt> must be the same as the
<tt class="literal"><span class="pre">Reference</span></tt> template parameter.</p>
<p>The <tt class="literal"><span class="pre">Value</span></tt> template parameter will be the <tt class="literal"><span class="pre">value_type</span></tt> for the
<tt class="literal"><span class="pre">indirect_iterator</span></tt>, unless <tt class="literal"><span class="pre">Value</span></tt> is cv-qualified. If <tt class="literal"><span class="pre">Value</span></tt>
is cv-qualified then <tt class="literal"><span class="pre">value_type</span></tt> will be non-qualified version of
the type. The default for <tt class="literal"><span class="pre">Value</span></tt> is</p>
<pre class="literal-block">
iterator_traits&lt; iterator_traits&lt;Iterator&gt;::value_type &gt;::value_type
</pre>
<p>If the default is used for <tt class="literal"><span class="pre">Value</span></tt>, then there must be a valid
specialization of <tt class="literal"><span class="pre">iterator_traits</span></tt> for the value type of the base
iterator.</p>
<p>The <tt class="literal"><span class="pre">Reference</span></tt> parameter will be the <tt class="literal"><span class="pre">reference</span></tt> type of the
<tt class="literal"><span class="pre">indirect_iterator</span></tt>. The default is <tt class="literal"><span class="pre">Value&amp;</span></tt>.</p>
<p>The <tt class="literal"><span class="pre">Access</span></tt> and <tt class="literal"><span class="pre">Traversal</span></tt> parameters are passed unchanged to
the corresponding parameters of the <tt class="literal"><span class="pre">iterator_adaptor</span></tt> base
class, and the <tt class="literal"><span class="pre">Iterator</span></tt> parameter is passed unchanged as the
<tt class="literal"><span class="pre">Base</span></tt> parameter to the <tt class="literal"><span class="pre">iterator_adaptor</span></tt> base class.</p>
<!-- THE ABOVE IS NO LONGER IN SYNC WITH THE CODE. -Jeremy -->
<p>The indirect iterator will model the most refined standard traversal
concept that is modeled by the <tt class="literal"><span class="pre">Iterator</span></tt> type. The indirect
iterator will model the most refined standard access concept that is
modeled by the value type of <tt class="literal"><span class="pre">Iterator</span></tt>.</p>
concept that is modeled by the <tt class="literal"><span class="pre">Iterator</span></tt> type and that refines the
traversal category specified in the <tt class="literal"><span class="pre">CategoryOrTraversal</span></tt> parameter.
The indirect iterator will model the most refined standard access
concept that is modeled by the value type of <tt class="literal"><span class="pre">Iterator</span></tt>.</p>
</div>
<div class="section" id="indirect-iterator-operations">
<h4><a class="toc-backref" href="#id43" name="indirect-iterator-operations"><tt class="literal"><span class="pre">indirect_iterator</span></tt> operations</a></h4>
@ -1507,8 +1321,8 @@ modeled by the value type of <tt class="literal"><span class="pre">Iterator</spa
<tbody valign="top">
<tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="literal"><span class="pre">Iterator</span></tt> must be Default Constructible.</td>
</tr>
<tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="literal"><span class="pre">indirect_iterator</span></tt> with
a default constructed base object.</td>
<tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="literal"><span class="pre">indirect_iterator</span></tt> with
a default-constructed <tt class="literal"><span class="pre">iterator_adaptor</span></tt> subobject.</td>
</tr>
</tbody>
</table>
@ -1540,7 +1354,8 @@ indirect_iterator(
<tbody valign="top">
<tr class="field"><th class="field-name">Requires:</th><td class="field-body"><tt class="literal"><span class="pre">Iterator2</span></tt> is implicitly convertible to <tt class="literal"><span class="pre">Iterator</span></tt>.</td>
</tr>
<tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="literal"><span class="pre">indirect_iterator</span></tt> that is a copy of <tt class="literal"><span class="pre">y</span></tt>.</td>
<tr class="field"><th class="field-name">Returns:</th><td class="field-body">An instance of <tt class="literal"><span class="pre">indirect_iterator</span></tt> whose
<tt class="literal"><span class="pre">iterator_adaptor</span></tt> subobject is constructed from <tt class="literal"><span class="pre">y.base()</span></tt>.</td>
</tr>
</tbody>
</table>
@ -2131,11 +1946,5 @@ LocalWords: OtherIncrementable Coplien -->
</div>
</div>
</div>
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4
doc/indirect_iterator_ref.rst
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@ -10,7 +10,7 @@
class indirect_iterator
: public iterator_adaptor<
indirect_iterator<Iterator, Value, Access, Traversal,
Reference, Difference>,
Reference, Difference>,
Iterator,
/* Value = see below */,
CategoryOrTraversal,
@ -101,6 +101,6 @@ concept that is modeled by the value type of ``Iterator``.
:Requires: ``Iterator2`` is implicitly convertible to ``Iterator``.
:Returns: An instance of ``indirect_iterator`` whose
``iterator_adaptor`` subobject is constructed from ``y.base()``.
``iterator_adaptor`` subobject is constructed from ``y.base()``.

104
doc/iter-issue-list.rst
View File

@ -52,7 +52,8 @@ specific values. Is there a reason for iterator_access to be more specific?
Resolution
----------
The iterator_access enum has been removed, so this is no longer an issue.
The iterator_access enum has been removed, so this is no longer an issue.
@ -267,6 +268,22 @@ argument's contained Iterator object should be converted to the target
type's Iterator type. Is that what's meant here?
Resolution
----------
1. As suggested, change the returns clause to read:
:Returns: An instance of ``indirect_iterator`` with a default-constructed
``iterator_adaptor`` subobject.
2. Basically, yes. The return clause should be changed to:
:Returns: An instance of ``indirect_iterator`` whose
``iterator_adaptor`` subobject is constructed from ``y.base()``.
Subject: N1530: enable_if_convertible conflicts with requires
=============================================================
Date: Wed, 12 Nov 2003 15:09:48 -0500
@ -389,8 +406,12 @@ iterator_facade, but does not provide the 'b' versions of these functions.
Are the 'b' versions needed?
Subject: Re: Proposed revision of N1550
=======================================
From: Pete Becker <petebecker@acm.org>
Date: Wed, 03 Dec 2003 13:36:26 -0500
Message c++std-lib-12566
========================
The footnote says:
@ -703,6 +724,10 @@ Date: Tue, 09 Dec 2003 13:35:20 -0500
From: Pete Becker <petebecker@acm.org>
Message c++std-lib-12640
Part 1
------
>The value_type of the Iterator template parameter should itself be
>dereferenceable. The return type of the operator* for the value_type must
>be the same type as the Reference template parameter.
@ -714,6 +739,25 @@ iterator_traits<Iterator>::value_type must be dereferenceable.
The Reference template parameter must be the same type as
*iterator_traits<Iterator>::value_type().
Resolution
----------
I don't think we want to require default constructible for
``iterator_traits<Iterator>::value_type``, so I've reworded to avoid
that implication.
Change the text to:
The following requirements are placed on the type
``iterator_traits<Iterator>::value_type``. Let ``i`` be an object of
type ``iterator_traits<Iterator>::value_type``. Then ``*i`` must be a
valid expression, and the type of ``*i`` must be the same as the
``Reference`` template parameter.
Part 2
------
>The Value template parameter will be the value_type for the
>indirect_iterator, unless Value is const. If Value is const X, then
>value_type will be non- const X.
@ -721,6 +765,23 @@ The Reference template parameter must be the same type as
Also non-volatile, right? In other words, if Value isn't use_default, it
just gets passed as the Value argument for iterator_adaptor.
Resolution
----------
Yes, I think that's right. Dave, can you confirm?
Here's the rewording:
The ``Value`` template parameter will be the ``value_type`` for the
``indirect_iterator``, unless ``Value`` is cv-qualified. If ``Value``
is cv-qualified then ``value_type`` will be non-qualified version of
the type.
Part 3
------
>The default for Value is
>
>iterator_traits< iterator_traits<Iterator>::value_type >::value_type
@ -734,6 +795,16 @@ pun, or is iterator_traits<Iterator>::value_type required to be some form
of iterator? If it's the former we need to find a different way to say it.
If it's the latter we need to say so.
Resolution
----------
Dave, help!
Part 4
------
>The Reference parameter will be the reference type of the
>indirect_iterator. The default is Value&.
@ -741,6 +812,15 @@ That is, the Reference parameter is passed unchanged as the Reference
argument to iterator_adaptor. Which is what it should say, instead of
repeating what iterator_adaptor does.
Resolution
----------
Yes.
Part 5
------
>The Access and Traversal parameters are passed unchanged to the
>corresponding parameters of the iterator_adaptor base class, and the
>Iterator parameter is passed unchanged as the Base parameter to the
@ -766,6 +846,15 @@ Reference, Difference>,
Reference,
Difference>
Resolution
----------
Yes.
Part 6
------
>The indirect iterator will model the most refined standard traversal
>concept that is modeled by the Iterator type. The indirect iterator will
>model the most refined standard access concept that is modeled by the
@ -777,6 +866,17 @@ most refined types are available, but iterator_traits<X>::iterator_category
won't reflect those capabilities.
Resolution
----------
The indirect iterator will model the most refined standard traversal
concept that is modeled by the ``Iterator`` type and that refines the
traversal category specified in the ``CategoryOrTraversal`` parameter.
The indirect iterator will model the most refined standard access
concept that is modeled by the value type of ``Iterator``.
.. I am not confident in the above. -JGS
Subject: N1530: transform_iterator requirements
===============================================