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[SVN r11563]
This commit is contained in:
Jeremy Siek 2001-11-04 04:37:14 +00:00
parent ec2ceb9c96
commit 84cdfb032c
2 changed files with 142 additions and 65 deletions
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59
iterator_adaptor_test.cpp
View File

@ -52,6 +52,7 @@
#include <boost/pending/iterator_tests.hpp>
#include <boost/pending/integer_range.hpp>
#include <boost/concept_archetype.hpp>
#include <boost/type_traits/same_traits.hpp>
#include <stdlib.h>
#include <vector>
#include <deque>
@ -97,6 +98,8 @@ typedef std::deque<int> storage;
typedef std::deque<int*> pointer_deque;
typedef std::set<storage::iterator> iterator_set;
template <class T> struct foo;
int
main()
{
@ -105,17 +108,54 @@ main()
const int N = sizeof(array)/sizeof(dummyT);
// sanity check, if this doesn't pass the test is buggy
boost::random_access_iterator_test(array,N,array);
boost::random_access_iterator_test(array, N, array);
#if 0
// Check that the policy concept checks and the default policy
// implementation match up.
boost::function_requires<
boost::RandomAccessIteratorPoliciesConcept<
boost::default_iterator_policies, int*,
boost::default_iterator_policies,
boost::iterator_adaptor<int*, boost::default_iterator_policies>,
boost::iterator<std::random_access_iterator_tag, int, std::ptrdiff_t,
int*, int&>
> >();
// Test the named parameters
{
// Test computation of defaults
typedef boost::iterator_adaptor<int*, boost::default_iterator_policies,
boost::value_type_is<int> > Iter1;
BOOST_STATIC_ASSERT((boost::is_same<std::iterator_traits<Iter1>::value_type, int>::value));
BOOST_STATIC_ASSERT((boost::is_same<std::iterator_traits<Iter1>::reference, int&>::value));
BOOST_STATIC_ASSERT((boost::is_same<std::iterator_traits<Iter1>::pointer, int*>::value));
BOOST_STATIC_ASSERT((boost::is_same<std::iterator_traits<Iter1>::difference_type, std::ptrdiff_t>::value));
BOOST_STATIC_ASSERT((boost::is_same<std::iterator_traits<Iter1>::iterator_category, std::random_access_iterator_tag>::value));
}
{
// Test computation of default when the Value is const
typedef boost::iterator_adaptor<int*, boost::default_iterator_policies,
boost::value_type_is<const int> > Iter1;
BOOST_STATIC_ASSERT((boost::is_same<std::iterator_traits<Iter1>::value_type, int>::value));
BOOST_STATIC_ASSERT((boost::is_same<std::iterator_traits<Iter1>::reference, const int&>::value));
BOOST_STATIC_ASSERT((boost::is_same<std::iterator_traits<Iter1>::pointer, const int*>::value));
}
{
// Test with no defaults
typedef boost::iterator_adaptor<int*, boost::default_iterator_policies,
boost::reference_is<long>,
boost::pointer_is<float>,
boost::value_type_is<char>,
boost::iterator_category_is<std::input_iterator_tag>,
boost::difference_type_is<int>
> Iter1;
BOOST_STATIC_ASSERT((boost::is_same<std::iterator_traits<Iter1>::value_type, char>::value));
BOOST_STATIC_ASSERT((boost::is_same<std::iterator_traits<Iter1>::reference, long>::value));
BOOST_STATIC_ASSERT((boost::is_same<std::iterator_traits<Iter1>::pointer, float>::value));
BOOST_STATIC_ASSERT((boost::is_same<std::iterator_traits<Iter1>::difference_type, int>::value));
BOOST_STATIC_ASSERT((boost::is_same<std::iterator_traits<Iter1>::iterator_category, std::input_iterator_tag>::value));
}
// Test the iterator_adaptor
{
boost::iterator_adaptor<dummyT*, boost::default_iterator_policies, dummyT> i(array);
@ -173,7 +213,7 @@ main()
typedef boost::reverse_iterator_generator<const dummyT*
#ifdef BOOST_NO_TEMPLATE_PARTIAL_SPECIALIZATION
, const dummyT
, dummyT, const dummyT&, const dummyT
#endif
>::type const_reverse_iterator;
@ -306,12 +346,12 @@ main()
#else
typedef boost::iterator_adaptor<boost::forward_iterator_archetype<dummyT>,
boost::default_iterator_policies,
boost::iterator_traits_generator
::value_type<dummyT>
::reference<const dummyT&>
::pointer<const dummyT*>
::iterator_category<std::forward_iterator_tag>
::difference_type<std::ptrdiff_t> > adaptor_type;
boost::reference_is<const dummyT&>,
boost::pointer_is<const dummyT*> ,
boost::iterator_category_is<std::forward_iterator_tag>,
boost::value_type_is<dummyT>,
boost::difference_type_is<std::ptrdiff_t>
> adaptor_type;
#endif
adaptor_type i(forward_iter);
int zero = 0;
@ -330,6 +370,7 @@ main()
if (zero) // don't do this, just make sure it compiles
assert((*i).m_x == i->foo());
}
#endif
std::cout << "test successful " << std::endl;
return 0;
}

144
iterator_adaptors.htm
View File

@ -26,6 +26,37 @@
"../../more/generic_programming.html#adaptors">adaptors</a> which apply
specific useful behaviors to arbitrary base iterators.
<h2>Backward Compatibility Note</h2>
<p>The library's interface has changed since it was first released, breaking
backward compatibility:
<ol>
<li><a href="#policies">Policies classes</a> now operate on instances of the
whole <tt>iterator_adaptor</tt> object, rather than just operating on the
<tt>Base</tt> object. This change not only gives the policies class access
to both members of a pair of interacting iterators, but also eliminates the
need for the ugly <tt>type&lt;Reference&gt;</tt> and
<tt>type&lt;Difference&gt;</tt> parameters to various policy functions.
<li>The <a href="#named_template_parameters">Named Template Parameter</a>
interface has been made simpler, easier to use, and compatible with more
compilers.
</ol>
<h2>Other Documentation</h2>
<p><a href="iterator_adaptors.pdf">``Policy Adaptors and the Boost Iterator
Adaptor Library''</a> is a technical paper describing this library and the
powerful design pattern on which it is based. It was presented at the <a
href="http://www.oonumerics.org/tmpw01">C++ Template Workshop</a> at OOPSLA
2001; the slides from the talk are available <a
href="iterator_adaptors.ppt">here</a>. Please note that while the slides
incorporate the minor interface changes described in the previous section,
the paper does not.
<h2>Table of Contents</h2>
<ul>
@ -183,7 +214,7 @@ struct iterator_adaptor;
particular, the result type of <tt>operator*()</tt>.<br>
<b>Default:</b> If <tt>Value</tt> is supplied, <tt>Value&amp;</tt> is
used. Otherwise
<tt>std::iterator_traits&lt;BaseType&gt;::reference</tt> is used.
<tt>std::iterator_traits&lt;BaseType&gt;::reference</tt> is used. <a href="#7">[7]</a>
<tr>
<td><tt>Pointer</tt>
@ -191,7 +222,7 @@ struct iterator_adaptor;
<td>The <tt>pointer</tt> type of the resulting iterator, and in
particular, the result type of <tt>operator-&gt;()</tt>.<br>
<b>Default:</b> If <tt>Value</tt> was supplied, then <tt>Value*</tt>,
otherwise <tt>std::iterator_traits&lt;BaseType&gt;::pointer</tt>.
otherwise <tt>std::iterator_traits&lt;BaseType&gt;::pointer</tt>. <a href="#7">[7]</a>
<tr>
<td><tt>Category</tt>
@ -385,40 +416,40 @@ typedef iterator_adaptor&lt;foo_iterator, foo_policies,
<pre>
struct <a name="default_iterator_policies">default_iterator_policies</a>
{
template &lt;class BaseType&gt;
void initialize(BaseType&amp;)
// Some of these members were defined static, but Borland got confused
// and thought they were non-const. Also, Sun C++ does not like static
// function templates.
template &lt;class Base&gt;
void initialize(Base&amp;)
{ }
template &lt;class Reference, class BaseType&gt;
Reference dereference(type&lt;Reference&gt;, const BaseType&amp; x) const
{ return *x; }
template &lt;class IteratorAdaptor&gt;
typename IteratorAdaptor::reference dereference(const IteratorAdaptor&amp; x) const
{ return *x.base(); }
template &lt;class BaseType&gt;
void increment(BaseType&amp; x)
{ ++x; }
template &lt;class IteratorAdaptor&gt;
void increment(IteratorAdaptor&amp; x)
{ ++x.base(); }
template &lt;class BaseType1, class BaseType2&gt;
bool equal(const BaseType1&amp; x, const BaseType2&amp; y) const
{ return x == y; }
template &lt;class IteratorAdaptor&gt;
void decrement(IteratorAdaptor&amp; x)
{ --x.base(); }
template &lt;class BaseType&gt;
void decrement(BaseType&amp; x)
{ --x; }
template &lt;class IteratorAdaptor, class DifferenceType&gt;
void advance(IteratorAdaptor&amp; x, DifferenceType n)
{ x.base() += n; }
template &lt;class BaseType, class DifferenceType&gt;
void advance(BaseType&amp; x, DifferenceType n)
{ x += n; }
template &lt;class IteratorAdaptor1, class IteratorAdaptor2&gt;
typename IteratorAdaptor1::difference_type
distance(const IteratorAdaptor1&amp; x, const IteratorAdaptor2&amp; y) const
{ return y.base() - x.base(); }
template &lt;class Difference, class BaseType1, class BaseType2&gt;
Difference distance(type&lt;Difference&gt;, const BaseType1&amp; x, const BaseType2&amp; y) const
{ return y - x; }
template &lt;class BaseType1, class BaseType2&gt;
bool less(const BaseType1&amp; x, const BaseType2&amp; y) const
{ return x &lt; y; }
template &lt;class IteratorAdaptor1, class IteratorAdaptor2&gt;
bool equal(const IteratorAdaptor1&amp; x, const IteratorAdaptor2&amp; y) const
{ return x.base() == y.base(); }
};
</pre>
</blockquote>
</pre></blockquote>
<p>Template member functions are used throughout
<tt>default_iterator_policies</tt> so that it can be employed with a wide
@ -451,7 +482,7 @@ struct <a name="default_iterator_policies">default_iterator_policies</a>
iterator_adaptor(const
iterator_adaptor&lt;B,Policies,V,R,P,Category,Distance&gt;&amp;)</tt>
<br><br>
This constructor allows for conversion from non-<tt>const</tt> to
This constructor allows for conversion from mutable to
constant adapted iterators. See <a href=
"#iterator_interactions">below</a> for more details.<br>
Requires: <tt>B</tt> is convertible to <tt>Base</tt>.
@ -483,34 +514,31 @@ struct <a name="default_iterator_policies">default_iterator_policies</a>
<p>To implement a transform iterator we will only change one of the base
iterator's behaviors, so the <tt>transform_iterator_policies</tt> class can
inherit the rest from <tt>default_iterator_policies</tt>. We will define
the <tt>dereference()</tt> member function, which is used to implement
inherit the rest from <tt>default_iterator_policies</tt>. We will define the
<tt>dereference()</tt> member function, which is used to implement
<tt>operator*()</tt> of the adapted iterator. The implementation will
dereference the base iterator and apply the function object. The
<tt>type&lt;Reference&gt;</tt> parameter is used to convey the appropriate
return type. The complete code for <tt>transform_iterator_policies</tt>
is:<br>
dereference the base iterator and apply the function object. The complete
code for <tt>transform_iterator_policies</tt> is:<br>
<br>
<blockquote>
<pre>
template &lt;class AdaptableUnaryFunction&gt;
struct transform_iterator_policies : public default_iterator_policies
{
<blockquote><pre>
template &lt;class AdaptableUnaryFunction&gt;
struct transform_iterator_policies : public default_iterator_policies
{
transform_iterator_policies() { }
transform_iterator_policies(const AdaptableUnaryFunction&amp; f)
: m_f(f) { }
template &lt;class Reference, class BaseIterator&gt;
Reference dereference(type&lt;Reference&gt;, const BaseIterator&amp; i) const
{ return m_f(*i); }
template &lt;class IteratorAdaptor&gt;
typename IteratorAdaptor::reference
dereference(const IteratorAdaptor&amp; iter) const
{ return m_f(*iter.base()); }
AdaptableUnaryFunction m_f;
};
</pre>
</blockquote>
};
</pre></blockquote>
<p>The next step is to use the <tt>iterator_adaptor</tt> template to
construct the transform iterator type. The nicest way to package the
@ -546,7 +574,7 @@ public:
<p>As a finishing touch, we will create an <a href=
"../../more/generic_programming.html#object_generator">object generator</a>
for the transform iterator. This is a function that makes it more
for the transform iterator. Our object generator makes it more
convenient to create a transform iterator.<br>
<br>
@ -785,12 +813,12 @@ bool operator==(const iterator_adaptor&lt;B1,P,V1,R1,P1,C,D&gt;&amp;,
<tt>reference</tt> types for all <a href=
"http://www.sgi.com/tech/stl/ForwardIterator.html">Forward Iterators</a> are
<tt>const T*</tt> and <tt>const T&amp;</tt>, respectively. Stripping the
<tt>const</tt>-ness of <tt>Value</tt> allows you to easily
make a <tt>const</tt> iterator adaptor by supplying a <tt>const</tt> type
for <tt>Value</tt>, and allowing the defaults for the <tt>Pointer</tt> and
<tt>Reference</tt> parameters to take effect. Although compilers that don't
support partial specialization won't strip <tt>const</tt> for you, having a
<tt>const value_type</tt> is often harmless in practice.
<tt>const</tt>-ness of <tt>Value</tt> allows you to easily make a constant
iterator by supplying a <tt>const</tt> type for <tt>Value</tt>, and allowing
the defaults for the <tt>Pointer</tt> and <tt>Reference</tt> parameters to
take effect. Although compilers that don't support partial specialization
won't strip <tt>const</tt> for you, having a <tt>const value_type</tt> is
often harmless in practice.
<p><a name="2">[2]</a> If your compiler does not support partial
specialization and the base iterator is a builtin pointer type, you
@ -856,6 +884,14 @@ bool operator==(const iterator_adaptor&lt;B1,P,V1,R1,P1,C,D&gt;&amp;,
*x = i;
</pre>
<p><a name="7">[7]</a>
If you are using a compiler that does not have a version of
<tt>std::iterator_traits</tt> that works for pointers (i.e., if your
compiler does not support partial specialization) then if the
<tt>Base</tt> type is a const pointer, then the correct defaults
for the <tt>reference</tt> and <tt>pointer</tt> types can not be
deduced. You must specify these types explicitly.
<hr>
<p>Revised