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<div class="section">
<div class="titlepage"><div><div><h2 class="title" style="clear: both">
<a name="boost_pfr.limitations_and_configuration"></a><a class="link" href="limitations_and_configuration.html" title="Limitations and Configuration">Limitations and
Configuration</a>
</h2></div></div></div>
<div class="caution"><table border="0" summary="Caution">
<tr>
<td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="../../../doc/src/images/caution.png"></td>
<th align="left">Caution</th>
</tr>
<tr><td align="left" valign="top"><p>
Recommended C++ Standards are C++17 and above. Library requires at least
C++14! Pre C++14 compilers (C++11, C++03...) are not supported.
</p></td></tr>
</table></div>
<p>
Boost.PFR library works with types that satisfy the requirements of <code class="computeroutput"><span class="identifier">SimpleAggregate</span></code>: aggregate types without
base classes, <code class="computeroutput"><span class="keyword">const</span></code> fields, references,
or C arrays:
</p>
<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">simple_aggregate</span> <span class="special">{</span> <span class="comment">// SimpleAggregate</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">name</span><span class="special">;</span>
<span class="keyword">int</span> <span class="identifier">age</span><span class="special">;</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">uuids</span><span class="special">::</span><span class="identifier">uuid</span> <span class="identifier">uuid</span><span class="special">;</span>
<span class="special">};</span>
<span class="keyword">struct</span> <span class="identifier">empty</span> <span class="special">{</span> <span class="comment">// SimpleAggregate</span>
<span class="special">};</span>
<span class="keyword">struct</span> <span class="identifier">aggregate</span> <span class="special">:</span> <span class="identifier">empty</span> <span class="special">{</span> <span class="comment">// not a SimpleAggregate</span>
<span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">name</span><span class="special">;</span>
<span class="keyword">int</span> <span class="identifier">age</span><span class="special">;</span>
<span class="identifier">boost</span><span class="special">::</span><span class="identifier">uuids</span><span class="special">::</span><span class="identifier">uuid</span> <span class="identifier">uuid</span><span class="special">;</span>
<span class="special">};</span>
</pre>
<p>
The library may work with aggregates that don't satisfy the requirements of
<code class="computeroutput"><span class="identifier">SimpleAggregate</span></code>, but the behavior
tends to be non-portable.
</p>
<h3>
<a name="boost_pfr.limitations_and_configuration.h0"></a>
<span class="phrase"><a name="boost_pfr.limitations_and_configuration.configuration_macro"></a></span><a class="link" href="limitations_and_configuration.html#boost_pfr.limitations_and_configuration.configuration_macro">Configuration
Macro</a>
</h3>
<p>
By default Boost.PFR <span class="bold"><strong>auto-detects your compiler abilities</strong></span>
and automatically defines the configuration macro into appropriate values.
If you wish to override that behavior, just define:
</p>
<div class="table">
<a name="boost_pfr.limitations_and_configuration.linkmacro"></a><p class="title"><b>Table 28.2. Macros</b></p>
<div class="table-contents"><table class="table" summary="Macros">
<colgroup>
<col>
<col>
</colgroup>
<thead><tr>
<th>
<p>
Macro name
</p>
</th>
<th>
<p>
Effect
</p>
</th>
</tr></thead>
<tbody>
<tr>
<td>
<p>
<span class="bold"><strong>BOOST_PFR_USE_CPP17</strong></span>
</p>
</td>
<td>
<p>
Define to <code class="computeroutput"><span class="number">1</span></code> if you wish
to override Boost.PFR choice and use C++17 structured bindings for
reflection. Define to <code class="computeroutput"><span class="number">0</span></code>
to override Boost.PFR choice and disable C++17 structured bindings
usage.
</p>
</td>
</tr>
<tr>
<td>
<p>
<span class="bold"><strong>BOOST_PFR_USE_LOOPHOLE</strong></span>
</p>
</td>
<td>
<p>
Define to <code class="computeroutput"><span class="number">1</span></code> if you wish
to override Boost.PFR choice and exploit <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_active.html#2118" target="_top">CWG
2118</a> for reflection. Define to <code class="computeroutput"><span class="number">0</span></code>
to override Boost.PFR choice and disable CWG 2118 usage.
</p>
</td>
</tr>
<tr>
<td>
<p>
<span class="bold"><strong>BOOST_PFR_USE_STD_MAKE_INTEGRAL_SEQUENCE</strong></span>
</p>
</td>
<td>
<p>
Define to <code class="computeroutput"><span class="number">0</span></code> if you are
hit by the template instantiation depth issues with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">make_integer_sequence</span></code> and wish
to use Boost.PFR version of that metafunction. Define to <code class="computeroutput"><span class="number">1</span></code> to override Boost.PFR detection logic.
</p>
</td>
</tr>
</tbody>
</table></div>
</div>
<br class="table-break"><h3>
<a name="boost_pfr.limitations_and_configuration.h1"></a>
<span class="phrase"><a name="boost_pfr.limitations_and_configuration.details_on_limitations"></a></span><a class="link" href="limitations_and_configuration.html#boost_pfr.limitations_and_configuration.details_on_limitations">Details
on Limitations</a>
</h3>
<p>
The Boost.PFRs reflection has some limitations that depend on a C++ Standard
and compiler capabilities:
</p>
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
<li class="listitem">
Static variables are ignored
</li>
<li class="listitem">
T must be aggregate initializable without empty base classes
</li>
<li class="listitem">
if T contains C arrays or it is inherited from non-empty type then the
result of reflection may differ depending on the C++ version and library
configuration
</li>
<li class="listitem">
Additional limitations if <span class="bold"><strong>BOOST_PFR_USE_CPP17 ==
0</strong></span>:
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
<li class="listitem">
Non of the member fields should have a template constructor from
one parameter.
</li>
<li class="listitem">
Additional limitations if <span class="bold"><strong>BOOST_PFR_USE_LOOPHOLE
== 0</strong></span>:
<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: square; ">
<li class="listitem">
T must be constexpr aggregate initializable and all its fields
must be constexpr default constructible
</li>
<li class="listitem">
<code class="computeroutput"><a class="link" href="../boost/pfr/get.html" title="Function get">boost::pfr::get</a></code>,
<code class="computeroutput"><a class="link" href="../boost/pfr/structure_to_tuple.html" title="Function template structure_to_tuple">boost::pfr::structure_to_tuple</a></code>,
<code class="computeroutput"><a class="link" href="../boost/pfr/structure_tie.html" title="Function structure_tie">boost::pfr::structure_tie</a></code>,
<code class="computeroutput"><a class="link" href="../reference_section.html#header.boost.pfr.core_hpp" title="Header &lt;boost/pfr/core.hpp&gt;">boost::pfr::tuple_element</a></code>
require T to be a POD type with built-in types only.
</li>
</ul></div>
</li>
</ul></div>
</li>
</ul></div>
</div>
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<td align="right"><div class="copyright-footer">Copyright © 2016-2021 Antony Polukhin<p>
Distributed under the Boost Software License, Version 1.0. (See accompanying
file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
</p>
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