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<div><h2 class="title">
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<a name="poly_collection"></a>Chapter 29. Boost.PolyCollection</h2></div>
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<div><div class="author"><h3 class="author">
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<span class="firstname">Joaquín M</span> <span class="surname">López Muñoz</span>
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<div><p class="copyright">Copyright © 2016-2021 Joaquín M López Muñoz</p></div>
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Distributed under the Boost Software License, Version 1.0. (See accompanying
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<div class="toc">
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<p><b>Table of Contents</b></p>
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<dl class="toc">
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<dt><span class="section"><a href="poly_collection.html#poly_collection.introduction">Introduction</a></span></dt>
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<dt><span class="section"><a href="poly_collection/an_efficient_polymorphic_data_st.html">An efficient
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polymorphic data structure</a></span></dt>
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<dt><span class="section"><a href="poly_collection/tutorial.html">Tutorial</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="poly_collection/tutorial.html#poly_collection.tutorial.basics">Basics</a></span></dt>
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<dt><span class="section"><a href="poly_collection/tutorial.html#poly_collection.tutorial.deeper_into_the_segmented_nature">Deeper
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into the segmented nature of Boost.PolyCollection</a></span></dt>
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<dt><span class="section"><a href="poly_collection/tutorial.html#poly_collection.tutorial.insertion_and_emplacement">Insertion
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and emplacement</a></span></dt>
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<dt><span class="section"><a href="poly_collection/tutorial.html#poly_collection.tutorial.exceptions">Exceptions</a></span></dt>
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<dt><span class="section"><a href="poly_collection/tutorial.html#poly_collection.tutorial.algorithms">Algorithms</a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="poly_collection/performance.html">Performance</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="poly_collection/performance.html#poly_collection.performance.container_definitions">Container
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definitions</a></span></dt>
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<dt><span class="section"><a href="poly_collection/performance.html#poly_collection.performance.insertion_tests">Insertion
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tests</a></span></dt>
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<dt><span class="section"><a href="poly_collection/performance.html#poly_collection.performance.processing_tests">Processing
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tests</a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="poly_collection/reference.html">Reference</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="poly_collection/reference.html#poly_collection.reference.polymorphism_models">Polymorphism
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models</a></span></dt>
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<dt><span class="section"><a href="poly_collection/reference.html#poly_collection.reference.polymorphic_containers">Polymorphic
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containers</a></span></dt>
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<dt><span class="section"><a href="poly_collection/reference.html#poly_collection.reference.header_boost_poly_collection_exc">Header
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<code class="computeroutput"><span class="string">"boost/poly_collection/exception.hpp"</span></code>
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synopsis</a></span></dt>
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<dt><span class="section"><a href="poly_collection/reference.html#poly_collection.reference.header_boost_poly_collection_bas">Header
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<code class="computeroutput"><span class="string">"boost/poly_collection/base_collection_fwd.hpp"</span></code>
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synopsis</a></span></dt>
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<dt><span class="section"><a href="poly_collection/reference.html#poly_collection.reference.header_boost_poly_collection_ba0">Header
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<code class="computeroutput"><span class="string">"boost/poly_collection/base_collection.hpp"</span></code>
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synopsis</a></span></dt>
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<dt><span class="section"><a href="poly_collection/reference.html#poly_collection.reference.header_boost_poly_collection_fun">Header
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<code class="computeroutput"><span class="string">"boost/poly_collection/function_collection_fwd.hpp"</span></code>
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synopsis</a></span></dt>
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<dt><span class="section"><a href="poly_collection/reference.html#poly_collection.reference.header_boost_poly_collection_fu0">Header
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<code class="computeroutput"><span class="string">"boost/poly_collection/function_collection.hpp"</span></code>
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synopsis</a></span></dt>
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<dt><span class="section"><a href="poly_collection/reference.html#poly_collection.reference.header_boost_poly_collection_any">Header
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<code class="computeroutput"><span class="string">"boost/poly_collection/any_collection_fwd.hpp"</span></code>
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synopsis</a></span></dt>
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<dt><span class="section"><a href="poly_collection/reference.html#poly_collection.reference.header_boost_poly_collection_an0">Header
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<code class="computeroutput"><span class="string">"boost/poly_collection/any_collection.hpp"</span></code>
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synopsis</a></span></dt>
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<dt><span class="section"><a href="poly_collection/reference.html#poly_collection.reference.header_boost_poly_collection_alg">Header
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<code class="computeroutput"><span class="string">"boost/poly_collection/algorithm.hpp"</span></code>
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synopsis</a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="poly_collection/future_work.html">Future work</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="poly_collection/future_work.html#poly_collection.future_work.alternative_rtti_systems">Alternative
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RTTI systems</a></span></dt>
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<dt><span class="section"><a href="poly_collection/future_work.html#poly_collection.future_work.copy_traits">Copy traits</a></span></dt>
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<dt><span class="section"><a href="poly_collection/future_work.html#poly_collection.future_work.parallel_algorithms">Parallel
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algorithms</a></span></dt>
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<dt><span class="section"><a href="poly_collection/future_work.html#poly_collection.future_work.variant_collection"><code class="computeroutput"><span class="identifier">variant_collection</span></code></a></span></dt>
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<dt><span class="section"><a href="poly_collection/future_work.html#poly_collection.future_work.ordered_polymorphic_collections">Ordered
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polymorphic collections</a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="poly_collection/release_notes.html">Release notes</a></span></dt>
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<dd><dl>
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<dt><span class="section"><a href="poly_collection/release_notes.html#poly_collection.release_notes.boost_1_76">Boost 1.76</a></span></dt>
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<dt><span class="section"><a href="poly_collection/release_notes.html#poly_collection.release_notes.boost_1_74">Boost 1.74</a></span></dt>
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<dt><span class="section"><a href="poly_collection/release_notes.html#poly_collection.release_notes.boost_1_73">Boost 1.73</a></span></dt>
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<dt><span class="section"><a href="poly_collection/release_notes.html#poly_collection.release_notes.boost_1_72">Boost 1.72</a></span></dt>
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<dt><span class="section"><a href="poly_collection/release_notes.html#poly_collection.release_notes.boost_1_71">Boost 1.71</a></span></dt>
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<dt><span class="section"><a href="poly_collection/release_notes.html#poly_collection.release_notes.boost_1_70">Boost 1.70</a></span></dt>
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<dt><span class="section"><a href="poly_collection/release_notes.html#poly_collection.release_notes.boost_1_69">Boost 1.69</a></span></dt>
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<dt><span class="section"><a href="poly_collection/release_notes.html#poly_collection.release_notes.boost_1_67">Boost 1.67</a></span></dt>
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<dt><span class="section"><a href="poly_collection/release_notes.html#poly_collection.release_notes.boost_1_66">Boost 1.66</a></span></dt>
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<dt><span class="section"><a href="poly_collection/release_notes.html#poly_collection.release_notes.boost_1_65">Boost 1.65</a></span></dt>
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</dl></dd>
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<dt><span class="section"><a href="poly_collection/acknowledgments.html">Acknowledgments</a></span></dt>
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</dl>
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</div>
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<div class="section">
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">
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<a name="poly_collection.introduction"></a><a class="link" href="poly_collection.html#poly_collection.introduction" title="Introduction">Introduction</a>
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</h2></div></div></div>
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<p>
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Dynamic polymorphism in C++ requires that objects (such as instances of classes
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derived from an abstract base) be accessed through an indirection pointer because
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their actual <span class="emphasis"><em>type</em></span> and <span class="emphasis"><em>size</em></span> are not
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known at the point of usage. As a consequence, regular containers cannot store
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polymorphic objects directly: the usual workaround is to have containers of
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pointers to heap-allocated elements. In modern computer architectures this
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pattern incurs two types of inefficiency:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem">
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The lack of memory contiguity produced by heap allocation degrades CPU
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cache performance.
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</li>
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<li class="listitem">
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Executing virtual operations on a sequence of polymorphic objects whose
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actual types differ from one to the next results in failures in <a href="https://en.wikipedia.org/wiki/Branch_predictor" target="_top">branch prediction</a>
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and a lower execution speed.
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</li>
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</ul></div>
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<p>
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When the particular traversal order is not relevant to the user application,
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Boost.PolyCollection proposes an alternative data structure that restores memory
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contiguity and packs elements according to their concrete type. Three container
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class templates are provided:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem">
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<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">base_collection</span></code>
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</li>
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<li class="listitem">
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<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">function_collection</span></code>
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</li>
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<li class="listitem">
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<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">any_collection</span></code>
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</li>
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</ul></div>
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<p>
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respectively dealing with three different types of dynamic polymorphism available
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in C++:
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</p>
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<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
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<li class="listitem">
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Classic base/derived or OOP polymorphism.
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</li>
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<li class="listitem">
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Function wrapping in the spirit of <a href="http://en.cppreference.com/w/cpp/utility/functional/function" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">function</span></code></a>.
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</li>
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<li class="listitem">
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So-called <a href="https://en.wikipedia.org/wiki/Duck_typing" target="_top"><span class="emphasis"><em>duck
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typing</em></span></a> as implemented by <a href="../../libs/type_erasure" target="_top">Boost.TypeErasure</a>.
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</li>
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</ul></div>
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<p>
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The interface of these containers closely follows that of standard containers.
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Additionally, the library provides versions of many of the standard library
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algorithms (including <a href="http://en.cppreference.com/w/cpp/algorithm/for_each" target="_top"><code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">for_each</span></code></a>)
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with improved performance and a special feature called <span class="emphasis"><em>type restitution</em></span>
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that allows user code to provide clues on the concrete types of the elements
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stored for further opportunities of increased efficiency related to inlining
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and <a href="http://hubicka.blogspot.com.es/2014/01/devirtualization-in-c-part-1.html" target="_top"><span class="emphasis"><em>devirtualization</em></span></a>.
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</p>
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<div class="note"><table border="0" summary="Note">
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<tr>
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<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../doc/src/images/note.png"></td>
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<th align="left">Note</th>
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</tr>
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<tr><td align="left" valign="top"><p>
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Boost.PolyCollection is a header-only library. C++11 support is required.
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The library has been verified to work with Visual Studio 2015, GCC 4.8 and
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Clang 3.3.
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</p></td></tr>
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</table></div>
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</div>
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</div>
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<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
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<td align="left"><p><small>Last revised: April 13, 2021 at 16:32:32 GMT</small></p></td>
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