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| <body> |
| <div class="document" id="boost-pointer-container-library"> |
| <h1 class="title"><img alt="Boost" src="boost.png" /> Pointer Container Library</h1> |
| <h2 class="subtitle" id="conventions">Conventions</h2> |
| <p>There are a few design decisions that will affect how the classes are |
| used. Besides these the classes are much like normal standard containers |
| and provides almost the same interface. The new conventions are:</p> |
| <div class="contents local topic"> |
| <ul class="simple"> |
| <li><a class="reference" href="#null-pointers-are-not-allowed-by-default" id="id3" name="id3">Null pointers are not allowed by default</a></li> |
| <li><a class="reference" href="#all-default-iterators-apply-an-extra-layer-of-indirection" id="id4" name="id4">All default iterators apply an extra layer of indirection</a></li> |
| <li><a class="reference" href="#all-comparison-operations-are-done-on-the-pointed-to-objects-and-not-at-the-pointer-level" id="id5" name="id5">All comparison operations are done on the pointed to objects and not at the pointer level</a></li> |
| <li><a class="reference" href="#stored-elements-are-required-to-be-cloneable-for-a-subset-of-the-operations" id="id6" name="id6">Stored elements are required to be Cloneable for a subset of the operations</a></li> |
| <li><a class="reference" href="#whenever-objects-are-inserted-into-a-container-they-are-cloned-before-insertion" id="id7" name="id7">Whenever objects are inserted into a container, they are cloned before insertion</a></li> |
| <li><a class="reference" href="#whenever-pointers-are-inserted-into-a-container-ownership-is-transferred-to-the-container" id="id8" name="id8">Whenever pointers are inserted into a container, ownership is transferred to the container</a></li> |
| <li><a class="reference" href="#ownership-can-be-transferred-from-a-container-on-a-per-pointer-basis" id="id9" name="id9">Ownership can be transferred from a container on a per pointer basis</a></li> |
| <li><a class="reference" href="#ownership-can-be-transferred-from-a-container-to-another-container-on-a-per-iterator-range-basis" id="id10" name="id10">Ownership can be transferred from a container to another container on a per iterator range basis</a></li> |
| <li><a class="reference" href="#a-container-can-be-cheaply-returned-from-functions-either-by-making-a-clone-or-by-giving-up-ownership-of-the-container" id="id11" name="id11">A container can be cheaply returned from functions either by making a clone or by giving up ownership of the container</a></li> |
| <li><a class="reference" href="#iterators-are-invalidated-as-in-the-corresponding-standard-container" id="id12" name="id12">Iterators are invalidated as in the corresponding standard container</a></li> |
| </ul> |
| </div> |
| <div class="section"> |
| <h1><a class="toc-backref" href="#id3" id="null-pointers-are-not-allowed-by-default" name="null-pointers-are-not-allowed-by-default">Null pointers are not allowed by default</a></h1> |
| <p>If the user tries to insert the null pointer, the operation will throw a |
| <tt class="docutils literal"><span class="pre">bad_pointer</span></tt> exception (see <a class="reference" href="examples.html">Example 1</a>).</p> |
| <p>Use <a class="reference" href="reference.html#class-nullable">nullable</a> to allow null pointers.</p> |
| <p>Please notice that all preconditions of the form</p> |
| <pre class="literal-block"> |
| x != 0; |
| </pre> |
| <p>are not active when the you have instantiated a container |
| with <tt class="docutils literal"><span class="pre">nullable<T></span></tt> as in</p> |
| <pre class="literal-block"> |
| boost::ptr_vector< boost::nullable<animal> > vec; |
| vec.push_back( 0 ); // ok |
| </pre> |
| </div> |
| <div class="section"> |
| <h1><a class="toc-backref" href="#id4" id="all-default-iterators-apply-an-extra-layer-of-indirection" name="all-default-iterators-apply-an-extra-layer-of-indirection">All default iterators apply an extra layer of indirection</a></h1> |
| <p>This is done to |
| make the containers easier and safer to use. It promotes a kind of |
| pointer-less programming and the user of a class needs not worry about |
| pointers except when allocating them (see <a class="reference" href="examples.html">Example 2</a>). Iterators that |
| provide access to the naked pointers are also provided since they might be |
| useful in rare cases. For example, whenever <tt class="docutils literal"><span class="pre">begin()</span></tt> returns an iterator, |
| <tt class="docutils literal"><span class="pre">ptr_begin()</span></tt> will return an iterator that allows one to iterate over the |
| stored pointers.</p> |
| </div> |
| <div class="section"> |
| <h1><a class="toc-backref" href="#id5" id="all-comparison-operations-are-done-on-the-pointed-to-objects-and-not-at-the-pointer-level" name="all-comparison-operations-are-done-on-the-pointed-to-objects-and-not-at-the-pointer-level">All comparison operations are done on the pointed to objects and not at the pointer level</a></h1> |
| <p>For example, in <tt class="docutils literal"><span class="pre">ptr_set<T></span></tt> the ordering is by default done by |
| <tt class="docutils literal"><span class="pre">boost::ptr_less<T></span></tt> which compares the indirected pointers. |
| Similarly, <tt class="docutils literal"><span class="pre">operator==()</span></tt> for <tt class="docutils literal"><span class="pre">container<Foo></span></tt> compares all objects |
| with <tt class="docutils literal"><span class="pre">operator==(const</span> <span class="pre">Foo&,</span> <span class="pre">const</span> <span class="pre">Foo&)</span></tt>.</p> |
| </div> |
| <div class="section"> |
| <h1><a id="stored-elements-are-required-to-be-cloneable-for-a-subset-of-the-operations" name="stored-elements-are-required-to-be-cloneable-for-a-subset-of-the-operations">Stored elements are required to be <a class="reference" href="reference.html#the-Cloneable-concept">Cloneable</a> for a subset of the operations</a></h1> |
| <p>This is because most polymorphic objects cannot be copied directly, but |
| they can often be so by a use of a member function (see <a class="reference" href="examples.html">Example 4</a>). Often |
| it does not even make sense to clone an object in which case a large |
| subset of the operations are still workable.</p> |
| </div> |
| <div class="section"> |
| <h1><a class="toc-backref" href="#id7" id="whenever-objects-are-inserted-into-a-container-they-are-cloned-before-insertion" name="whenever-objects-are-inserted-into-a-container-they-are-cloned-before-insertion">Whenever objects are inserted into a container, they are cloned before insertion</a></h1> |
| <p>This is necessary because all pointer containers take ownerships of stored objects |
| (see <a class="reference" href="examples.html">Example 5</a>).</p> |
| </div> |
| <div class="section"> |
| <h1><a class="toc-backref" href="#id8" id="whenever-pointers-are-inserted-into-a-container-ownership-is-transferred-to-the-container" name="whenever-pointers-are-inserted-into-a-container-ownership-is-transferred-to-the-container">Whenever pointers are inserted into a container, ownership is transferred to the container</a></h1> |
| <p>All containers take ownership of the stored pointers and therefore a |
| container needs to have its own copies (see <a class="reference" href="examples.html">Example 5</a>).</p> |
| </div> |
| <div class="section"> |
| <h1><a class="toc-backref" href="#id9" id="ownership-can-be-transferred-from-a-container-on-a-per-pointer-basis" name="ownership-can-be-transferred-from-a-container-on-a-per-pointer-basis">Ownership can be transferred from a container on a per pointer basis</a></h1> |
| <p>This can of course also be convenient. Whenever it happens, an |
| <tt class="docutils literal"><span class="pre">SmartContainer::auto_type</span></tt> object is used to provide an exception-safe transfer |
| (see <a class="reference" href="examples.html">Example 6</a>).</p> |
| </div> |
| <div class="section"> |
| <h1><a class="toc-backref" href="#id10" id="ownership-can-be-transferred-from-a-container-to-another-container-on-a-per-iterator-range-basis" name="ownership-can-be-transferred-from-a-container-to-another-container-on-a-per-iterator-range-basis">Ownership can be transferred from a container to another container on a per iterator range basis</a></h1> |
| <p>This makes it possible to exchange data safely between different pointer |
| containers without cloning the objects again (see <a class="reference" href="examples.html">Example 7</a>).</p> |
| </div> |
| <div class="section"> |
| <h1><a class="toc-backref" href="#id11" id="a-container-can-be-cheaply-returned-from-functions-either-by-making-a-clone-or-by-giving-up-ownership-of-the-container" name="a-container-can-be-cheaply-returned-from-functions-either-by-making-a-clone-or-by-giving-up-ownership-of-the-container">A container can be cheaply returned from functions either by making a clone or by giving up ownership of the container</a></h1> |
| <p>Two special member functions, <tt class="docutils literal"><span class="pre">clone()</span></tt> and <tt class="docutils literal"><span class="pre">release()</span></tt>, both return an |
| <tt class="docutils literal"><span class="pre">auto_ptr<SmartContainer></span></tt> which can be assigned to another pointer container. This |
| effectively reduces the cost of returning a container to one |
| heap-allocation plus a call to <tt class="docutils literal"><span class="pre">swap()</span></tt> (see <a class="reference" href="examples.html">Example 3</a>).</p> |
| </div> |
| <div class="section"> |
| <h1><a class="toc-backref" href="#id12" id="iterators-are-invalidated-as-in-the-corresponding-standard-container" name="iterators-are-invalidated-as-in-the-corresponding-standard-container">Iterators are invalidated as in the corresponding standard container</a></h1> |
| <p>Because the containers in this library wrap standard containers, the |
| rules for invalidation of iterators are the same as the rules |
| of the corresponding standard container.</p> |
| <p>For example, for both <tt class="docutils literal"><span class="pre">boost::ptr_vector<T></span></tt> and <tt class="docutils literal"><span class="pre">std::vector<U></span></tt> |
| insertion and deletion only invalidates the deleted |
| element and elements following it; all elements before the inserted/deleted |
| element remain valid.</p> |
| <hr><p><strong>Navigate:</strong></p> |
| <ul class="simple"> |
| <li><a class="reference" href="ptr_container.html">home</a></li> |
| <li><a class="reference" href="reference.html">reference</a></li> |
| </ul> |
| <hr><table class="docutils field-list" frame="void" rules="none"> |
| <col class="field-name" /> |
| <col class="field-body" /> |
| <tbody valign="top"> |
| <tr class="field"><th class="field-name">Copyright:</th><td class="field-body">Thorsten Ottosen 2004-2006. Use, modification and distribution is subject to the Boost Software License, Version 1.0 (see <a class="reference" href="http://www.boost.org/LICENSE_1_0.txt">LICENSE_1_0.txt</a>).</td> |
| </tr> |
| </tbody> |
| </table> |
| </div> |
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