mirror of
https://github.com/boostorg/utility.git
synced 2025-05-09 15:04:00 +00:00
added section on Members to cover constructors, etc. and added
a section on Operators [SVN r9206]
This commit is contained in:
Jeremy Siek
parent
7e25450054
commit
84f1ffdefe
@ -52,14 +52,6 @@
|
||||
<a href="counting_iterator.htm">Counting Iterator Adaptor</a>
|
||||
</ul>
|
||||
|
||||
<!-- not sure where this paragraph was going...
|
||||
defines the <tt>iterator_adaptor</tt> class template and several <a href=
|
||||
"../../more/generic_programming.html#type_generator">type generators</a>
|
||||
and <a href="../../more/generic_programming.html#object_generator">object
|
||||
generators</a> which allow you to easily create adapted iterator types. The
|
||||
Iterator Adaptors
|
||||
-->
|
||||
|
||||
<p><b><a href="http://www.boost.org/people/dave_abrahams.htm">Dave
|
||||
Abrahams</a></b> started the library, applying <a href=
|
||||
"../../more/generic_programming.html#policies">policies class</a> technique
|
||||
@ -109,16 +101,16 @@ struct iterator_adaptor;
|
||||
typedef Reference reference;
|
||||
typedef Category iterator_category;
|
||||
typedef Base base_type;
|
||||
typedef Policies policies_type;
|
||||
|
||||
iterator_adaptor();
|
||||
iterator_adaptor(const Base&, const Policies& = Policies());
|
||||
|
||||
base_type base() const;
|
||||
|
||||
template <class Iter2, class Value2, class Pointer2, class Reference2>
|
||||
template <class B, class V, class R, class P>
|
||||
iterator_adaptor (
|
||||
const iterator_adaptor<Iter2,Policies,Value2,Reference2,Pointer2,Category,Distance>&
|
||||
: m_iter_p(src.iter(), src.policies());
|
||||
const iterator_adaptor<B,Policies,V,R,P,Category,Distance>&);
|
||||
|
||||
reference operator*() const;
|
||||
<i>operator_arrow_result_type</i> operator->() const; <a href="#2">[2]</a>
|
||||
@ -135,50 +127,27 @@ struct iterator_adaptor;
|
||||
iterator_adaptor& operator-(Distance x) const;
|
||||
};
|
||||
|
||||
template <class B, class Policies, class V, class R, class P,
|
||||
template <class B, class P, class V, class R, class Ptr,
|
||||
class C, class D1, class D2>
|
||||
iterator_adaptor<B,Policies,V,R,P,C,D1>
|
||||
operator+(iterator_adaptor<B,P,V,R,P,C,D1>, D2);
|
||||
iterator_adaptor<B,P,V,R,Ptr,C,D1>
|
||||
operator+(iterator_adaptor<B,P,V,R,Ptr,C,D1>, D2);
|
||||
|
||||
template <class B, class Policies, class V, class R, class P,
|
||||
template <class B, class P, class V, class R, class Ptr,
|
||||
class C, class D1, class D2>
|
||||
iterator_adaptor<B,Policies,V,R,P,C,D1>
|
||||
operator+(D2, iterator_adaptor<B,P,V,R,P,C,D1> p);
|
||||
iterator_adaptor<B,P,V,R,P,C,D1>
|
||||
operator+(D2, iterator_adaptor<B,P,V,R,Ptr,C,D1> p);
|
||||
|
||||
template <class B1, class B2, class Policies, class V1, class V2,
|
||||
template <class B1, class B2, class P, class V1, class V2,
|
||||
class R1, class R2, class P1, class P2, class C, class D>
|
||||
Distance operator-(const iterator_adaptor<B1,P,V1,R1,P1,C,D>&,
|
||||
const iterator_adaptor<B2,P,V2,R2,P2,C,D>&);
|
||||
|
||||
template <class B1, class B2, class Policies, class V1, class V2,
|
||||
template <class B1, class B2, class P, class V1, class V2,
|
||||
class R1, class R2, class P1, class P2, class C, class D>
|
||||
bool operator==(const iterator_adaptor<B1,P,V1,R1,P1,C,D>&,
|
||||
const iterator_adaptor<B2,P,V2,R2,P2,C,D>&);
|
||||
|
||||
template <class B1, class B2, class Policies, class V1, class V2,
|
||||
class R1, class R2, class P1, class P2, class C, class D>
|
||||
bool operator!=(const iterator_adaptor<B1,P,V1,R1,P1,C,D>&,
|
||||
const iterator_adaptor<B2,P,V2,R2,P2,C,D>&);
|
||||
|
||||
template <class B1, class B2, class Policies, class V1, class V2,
|
||||
class R1, class R2, class P1, class P2, class C, class D>
|
||||
bool operator<(const iterator_adaptor<B1,P,V1,R1,P1,C,D>&,
|
||||
const iterator_adaptor<B2,P,V2,R2,P2,C,D>&);
|
||||
|
||||
template <class B1, class B2, class Policies, class V1, class V2,
|
||||
class R1, class R2, class P1, class P2, class C, class D>
|
||||
bool operator<=(const iterator_adaptor<B1,P,V1,R1,P1,C,D>&,
|
||||
const iterator_adaptor<B2,P,V2,R2,P2,C,D>&);
|
||||
|
||||
template <class B1, class B2, class Policies, class V1, class V2,
|
||||
class R1, class R2, class P1, class P2, class C, class D>
|
||||
bool operator>=(const iterator_adaptor<B1,P,V1,R1,P1,C,D>&,
|
||||
const iterator_adaptor<B2,P,V2,R2,P2,C,D>&);
|
||||
|
||||
template <class B1, class B2, class Policies, class V1, class V2,
|
||||
class R1, class R2, class P1, class P2, class C, class D>
|
||||
bool operator>(const iterator_adaptor<B1,P,V1,R1,P1,C,D>&,
|
||||
const iterator_adaptor<B2,P,V2,R2,P2,C,D>&);
|
||||
// and similarly for operators !=, <, <=, >=, >
|
||||
</pre>
|
||||
|
||||
<h3>Example</h3>
|
||||
@ -234,7 +203,7 @@ bool operator>(const iterator_adaptor<B1,P,V1,R1,P1,C,D>&,
|
||||
policy class inherit from <tt>default_iterator_policies</tt> to avoid
|
||||
retyping the usual behaviors. You should also look at
|
||||
<tt>default_iterator_policies</tt> as the ``boiler-plate'' for your own
|
||||
policy classes. The following is definition of the
|
||||
policy classes. The following is the definition of the
|
||||
<tt>default_iterator_policies</tt> class:
|
||||
|
||||
<p>
|
||||
@ -276,7 +245,6 @@ struct default_iterator_policies
|
||||
</pre>
|
||||
</blockquote>
|
||||
|
||||
|
||||
To implement a transform iterator we will only change one of the
|
||||
base iterator's behaviors, so the
|
||||
<tt>transform_iterator_policies</tt> class will inherit the rest
|
||||
@ -287,8 +255,9 @@ struct default_iterator_policies
|
||||
value type of the base iterator) and we will need to know the
|
||||
<tt>result_type</tt> of the function, so
|
||||
<a href="http://www.sgi.com/Technology/STL/AdaptableUnaryFunction.html">
|
||||
AdaptableUnaryFunction</a> is the correct concept (set of
|
||||
requirements) to choose for the function object type. Inside of
|
||||
AdaptableUnaryFunction</a> is the correct
|
||||
<a href="../../more/generic_programming.html#concept">
|
||||
concept</a> to choose for the function object type. Inside of
|
||||
<tt>transform_iterator_policies</tt> we will implement the
|
||||
<tt>dereference()</tt> member function. This member function will
|
||||
dereference the base iterator (the second parameter of
|
||||
@ -321,13 +290,11 @@ struct default_iterator_policies
|
||||
construct the transform iterator type. The nicest way to package
|
||||
up the construction of the transform iterator is to create a <a
|
||||
href="../../more/generic_programming.html#type_generator">type
|
||||
generator</a>, which is a class whose sole purpose is to
|
||||
create a typedef for some new type based on several template
|
||||
parameters. The first template parameter will be the type of the
|
||||
function object and the second will be the base iterator
|
||||
type. Inside the <tt>transform_iterators</tt> class we use the
|
||||
<tt>iterator_adaptor</tt> class to create the transform iterator
|
||||
type.
|
||||
generator</a>. The first template parameter of the generator will
|
||||
be the type of the function object and the second will be the base
|
||||
iterator type. Inside the <tt>transform_iterator_generator</tt>
|
||||
class we use the <tt>iterator_adaptor</tt> class to create the
|
||||
transform iterator type.
|
||||
|
||||
<p>
|
||||
<blockquote>
|
||||
@ -405,18 +372,9 @@ This output is:
|
||||
<th>Description
|
||||
|
||||
<tr>
|
||||
<td><a href=
|
||||
"http://www.sgi.com/tech/stl/Predicate.html"><tt>Predicate</tt></a>
|
||||
<td><tt>Base</tt>
|
||||
|
||||
<td>The function object that determines which elements are retained and
|
||||
which elements are skipped.
|
||||
|
||||
<tr>
|
||||
<td><tt>BaseIterator</tt>
|
||||
|
||||
<td>The iterator type being wrapped. This type must at least be a model
|
||||
of the <a href=
|
||||
"http://www.sgi.com/tech/stl/InputIterator">InputIterator</a> concept.
|
||||
<td>The type being wrapped.
|
||||
|
||||
<tr>
|
||||
<td><tt>Value</tt>
|
||||
@ -451,10 +409,7 @@ This output is:
|
||||
<td><tt>Category</tt>
|
||||
|
||||
<td>The <tt>iterator_category</tt> type for the resulting iterator.
|
||||
Typically the default for this parameter is the appropriate type. If
|
||||
you override this parameter, do not use
|
||||
<tt>bidirectional_iterator_tag</tt> because filter iterators can not go
|
||||
in reverse.<br>
|
||||
Typically the default for this parameter is the appropriate type.<br>
|
||||
<b>Default:</b>
|
||||
<tt>std::iterator_traits<BaseIterator>::iterator_category</tt>
|
||||
|
||||
@ -468,6 +423,65 @@ This output is:
|
||||
</table>
|
||||
|
||||
|
||||
<h3>Model of</h3>
|
||||
|
||||
Depending on the <tt>Base</tt> and <tt>Policies</tt> template
|
||||
parameters, an <tt>iterator_adaptor</tt> can be a <a
|
||||
href="http://www.sgi.com/tech/stl/InputIterator.html"> Input
|
||||
Iterator</a>, <a
|
||||
href="http://www.sgi.com/tech/stl/ForwardIterator.html"> Forward
|
||||
Iterator</a>, <a
|
||||
href="http://www.sgi.com/tech/stl/BidirectionalIterator.html">
|
||||
Bidirectional Iterator</a>, or <a
|
||||
href="http://www.sgi.com/tech/stl/RandomAccessIterator.html">
|
||||
Random Access Iterator</a>.
|
||||
|
||||
<h3>Members</h3>
|
||||
|
||||
In addition to all of the member functions required of a <a
|
||||
href="http://www.sgi.com/tech/stl/RandomAccessIterator.html">
|
||||
Random Access Iterator</a>, the <tt>iterator_adaptor</tt> class
|
||||
template defines the following members.
|
||||
|
||||
<p>
|
||||
<table border>
|
||||
<tr><td><tt>
|
||||
iterator_adaptor(const Base&, const Policies& = Policies())
|
||||
</tt><br>
|
||||
Construct an iterator adaptor from a base object and a policies object.
|
||||
</td></tr>
|
||||
|
||||
<tr><td><tt>
|
||||
template <class B, class V, class R, class P><br>
|
||||
iterator_adaptor(const iterator_adaptor<B,Policies,V,R,P,Category,Distance>&)
|
||||
</tt><br><br>
|
||||
This constructor allows for conversion from mutable to constant iterator
|
||||
adaptors. This assumes that the type <tt>B</tt> is convertible to the
|
||||
type <tt>Base</tt>.
|
||||
</td></tr>
|
||||
|
||||
<tr><td><tt>
|
||||
base_type base() const;
|
||||
</tt><br><br>
|
||||
Return a copy of the base object.
|
||||
</td></tr>
|
||||
|
||||
</table>
|
||||
|
||||
<h3>Operators</h3>
|
||||
|
||||
The <tt>iterator_adaptor</tt> class defines all of the operators
|
||||
required of a
|
||||
<a href="http://www.sgi.com/tech/stl/RandomAccessIterator.html">
|
||||
Random Access Iterator</a>. Also, the operators of the
|
||||
<tt>iterator_adaptor</tt> class that take two iterator adaptor
|
||||
arguments (difference and comparisons) are defined in such a way
|
||||
that the operators work on pairs of <tt>iterator_adaptor</tt>
|
||||
types that have different template parameters, provided that the
|
||||
base types of the iterator adaptors are interoperable. The reason
|
||||
for this is so that mutable and constant versions of an iterator
|
||||
adaptor can be created that will be interoperable with eachother.
|
||||
|
||||
<h3>Challenge</h3>
|
||||
|
||||
<p>There is an unlimited number of ways the the
|
||||
@ -490,6 +504,20 @@ This output is:
|
||||
in a stardard conforming fashion, providing access to members
|
||||
of the objects pointed to by the iterator.
|
||||
|
||||
<h3>Implemenation Notes</h3>
|
||||
|
||||
<ul>
|
||||
<li>The <tt>iterator_adaptor::operator[]</tt> returns by-value
|
||||
instead of by-reference as might be expected. There are two
|
||||
reasons for this. First, the C++ standard only requires that
|
||||
the return type by ``convertible to T'' (Table 76). Second,
|
||||
and more importantly, for certain kinds of iterators,
|
||||
returning a reference could cause serious memory problems due
|
||||
to the reference being bound to a temporary object whose
|
||||
lifetime ends inside of the <tt>operator[]</tt>.</li>
|
||||
|
||||
</ul>
|
||||
|
||||
<hr>
|
||||
|
||||
<p>Revised
|
||||
|
||||
Loading…
x
Reference in New Issue
Block a user