variant/doc/reference/multivisitor.xml

<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE header PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN"
  "http://www.boost.org/tools/boostbook/dtd/boostbook.dtd">
<!--
    Copyright 2013-2025 Antony Polukhin.

    Distributed under the Boost Software License, Version 1.0. (See accompanying
    file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
-->
<header name="boost/variant/multivisitors.hpp">
  <using-namespace name="boost"/>

  <para>Provides declarations of <functionname>apply_visitor</functionname> for three or more
    <code><classname>variant</classname></code> parameters.</para>

  <namespace name="boost">
    <overloaded-function name="apply_visitor /*three or more variant parameters*/">
      <description>
        <simpara>Allows compile-time checked type-safe application of the
        given visitor to the content of the given variant, ensuring that all
        types are handled by the visitor. See <functionname>apply_visitor</functionname>
        for more information.</simpara>
      </description>

      <signature>
        <template>
          <template-type-parameter name="MultiVisitor"/>
          <template-type-parameter name="Variant1"/>
          <template-type-parameter name="Variant2"/>
          <template-type-parameter name="Variant3"/>
        </template>

        <type>typename MultiVisitor::result_type OR decltype(auto)</type>

        <parameter name="visitor">
          <paramtype>MultiVisitor &amp;</paramtype>
        </parameter>
        <parameter name="operand1">
          <paramtype>Variant1&amp;&amp;</paramtype>
        </parameter>
        <parameter name="operand2">
          <paramtype>Variant2&amp;&amp;</paramtype>
        </parameter>
        <parameter name="operand3">
          <paramtype>Variant3&amp;&amp;</paramtype>
        </parameter>
        <parameter name="other_operands">
          <paramtype>...</paramtype>
        </parameter>
      </signature>

      <signature>
        <template>
          <template-type-parameter name="MultiVisitor"/>
          <template-type-parameter name="Variant1"/>
          <template-type-parameter name="Variant2"/>
          <template-type-parameter name="Variant3"/>
        </template>

        <type>typename MultiVisitor::result_type OR decltype(auto)</type>

        <parameter name="visitor">
          <paramtype>const MultiVisitor &amp;</paramtype>
        </parameter>
        <parameter name="operand1">
          <paramtype>Variant1&amp;&amp;</paramtype>
        </parameter>
        <parameter name="operand2">
          <paramtype>Variant2&amp;&amp;</paramtype>
        </parameter>
        <parameter name="operand3">
          <paramtype>Variant3&amp;&amp;</paramtype>
        </parameter>
        <parameter name="other_operands">
          <paramtype>...</paramtype>
        </parameter>
      </signature>
    </overloaded-function>
  </namespace>
</header>