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added not about constness of operator* and operator[]

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[SVN r10931]
This commit is contained in:
Jeremy Siek 2001-08-24 15:28:20 +00:00
parent 6392e2788f
commit 75c9dd3be1
1 changed files with 33 additions and 3 deletions
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36
iterator_adaptors.htm
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@ -767,10 +767,10 @@ struct iterator_adaptor
iterator_adaptor(
const iterator_adaptor<B,Policies,V,R,P,Category,Distance>&);
reference operator*() const;
reference operator*() const; <a href="#6">[6]</a>
<i>operator_arrow_result_type</i> operator-&gt;() const; <a href=
"#3">[3]</a>
<i>value_type</i> operator[](difference_type n) const; <a href="#3">[4]</a>
<i>value_type</i> operator[](difference_type n) const; <a href="#3">[4]</a>, <a href="#6">[6]</a>
iterator_adaptor&amp; operator++();
iterator_adaptor&amp; operator++(int);
@ -857,6 +857,34 @@ bool operator==(const iterator_adaptor&lt;B1,P,V1,R1,P1,C,D&gt;&amp;,
Forward Iterator</a>, so you will need to use a less restrictive
iterator category such as <tt>std::input_iterator_tag</tt>.
<p><a name="6">[6]</a>
There is a common misconception that an iterator should have two
versions of <tt>operator*</tt> and of <tt>operator[]</tt>, one
version that is a <tt>const</tt> member function and one version
that is non-<tt>const</tt>. Perhaps the source of this
misconception is that containers typically have const and
non-const versions of many of their member functions. Iterators,
however, are different. A particular iterator type can be either
<i>mutable</i> or <i>constant</i> (but not both). One can assign
to and change the object pointed to by a mutable iterator whereas a
constant iterator returns constant objects when dereferenced. Whether
the iterator object itself is <tt>const</tt> has nothing to do with
whether the iterator is mutable or constant. This is analogous to
the way built-in pointer types behave. For example, one can
modify objects pointed to by a <tt>const</tt> pointer
<pre>
int* const x = new int;
int i = 3;
*x = i;
</pre>
but one cannot modify objects pointed to by a pointer
to <tt>const</tt>
<pre>
int const* x = new int;
int i = 3;
*x = i;
</pre>
<hr>
<p>Revised
@ -871,7 +899,7 @@ bool operator==(const iterator_adaptor&lt;B1,P,V1,R1,P1,C,D&gt;&amp;,
</body>
<!-- LocalWords: HTML html charset alt gif abrahams htm const
<!-- LocalWords: HTML html charset alt gif abrahams htm const iterator
incrementable david abrahams
-->
@ -887,5 +915,7 @@ bool operator==(const iterator_adaptor&lt;B1,P,V1,R1,P1,C,D&gt;&amp;,
<!-- LocalWords: iostream hpp sizeof InputIterator constness ConstIterator
David Abrahams
-->
<!-- LocalWords: Iterators dereferenced
-->
</html>