source: downloads/boost_1_33_1/libs/variant/doc/reference/recursive_wrapper.xml @ 20

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<!DOCTYPE header PUBLIC "-//Boost//DTD BoostBook XML V1.0//EN"
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<header name="boost/variant/recursive_wrapper.hpp">
  <namespace name="boost">

    <class name="recursive_wrapper">
      <purpose>Solves circular dependencies, enabling recursive types.</purpose>

      <template>
        <template-type-parameter name="T"/>
      </template>

      <description>
        <simpara>The <code>recursive_wrapper</code> class template has an
          interface similar to a simple value container, but its content is
          allocated dynamically. This allows <code>recursive_wrapper</code> to
          hold types <code>T</code> whose member data leads to a circular
          dependency (e.g., a data member of <code>T</code> has a data member
          of type <code>T</code>).</simpara>

        <simpara>The application of <code>recursive_wrapper</code> is easiest
          understood in context. See
          <xref linkend="variant.tutorial.recursive.recursive-wrapper"/> for a
          demonstration of a common use of the class template.</simpara>

        <simpara><emphasis role="bold">Notes</emphasis>:</simpara>
        <itemizedlist>
          <listitem>Any type specified as the template argument to
            <code>recursive_wrapper</code> must be capable of construction via
            <code>operator new</code>. Thus, for instance, references are not
            supported.</listitem>
        </itemizedlist>
      </description>

      <typedef name="type">
        <type>T</type>
      </typedef>

      <destructor>
        <purpose>Destructor.</purpose>
        <description>
          <simpara>Deletes the content of <code>*this</code>.</simpara>
        </description>

        <throws>Will not throw.</throws>
      </destructor>

      <constructor>
        <purpose>Default constructor.</purpose>
        <description>
          <simpara>Initializes <code>*this</code> by default construction of
            <code>T</code>.</simpara>
        </description>

        <requires>
          <simpara><code>T</code> must fulfill the requirements of the
            <emphasis>DefaultConstructible</emphasis> [20.1.4]
            concept.</simpara>
        </requires>

        <throws>
          <simpara>May fail with any exceptions arising from the default
            constructor of <code>T</code> or, in the event of
            insufficient memory, with <code>std::bad_alloc</code>.</simpara>
        </throws>
      </constructor>

      <constructor>
        <parameter name="other">
          <paramtype>const recursive_wrapper &amp;</paramtype>
        </parameter>

        <purpose>Copy constructor.</purpose>
        <description>
          <simpara>Copies the content of <code>other</code> into
            <code>*this</code>.</simpara>
        </description>

        <throws>
          <simpara>May fail with any exceptions arising from the
            copy constructor of <code>T</code> or, in the event of
            insufficient memory, with <code>std::bad_alloc</code>.</simpara>
        </throws>
      </constructor>

      <constructor>
        <parameter name="operand">
          <paramtype>const T &amp;</paramtype>
        </parameter>

        <purpose>Value constructor.</purpose>
        <description>
          <simpara>Copies <code>operand</code> into
            <code>*this</code>.</simpara>
        </description>

        <throws>
          <simpara>May fail with any exceptions arising from the
            copy constructor of <code>T</code> or, in the event of
            insufficient memory, with <code>std::bad_alloc</code>.</simpara>
        </throws>
      </constructor>

      <method-group name="modifiers">

        <method name="swap">
          <type>void</type>

          <parameter name="other">
            <paramtype>recursive_wrapper &amp;</paramtype>
          </parameter>

          <description>
            <simpara>Exchanges contents of <code>*this</code> and
              <code>other</code>.</simpara>
          </description>

          <throws>Will not throw.</throws>
        </method>

        <method name="operator=">
          <type>recursive_wrapper &amp;</type>

          <parameter name="rhs">
            <paramtype>const recursive_wrapper &amp;</paramtype>
          </parameter>

          <purpose>Copy assignment operator.</purpose>
          <description>
            <simpara>Assigns the content of <code>rhs</code> to the content of
              <code>*this</code>.</simpara>
          </description>

          <requires>
            <simpara><code>T</code> must fulfill the requirements of
            the <conceptname>Assignable</conceptname>
            concept.</simpara>
          </requires>

          <throws>
            <simpara>May fail with any exceptions arising from the assignment
              operator of <code>T</code>.</simpara>
          </throws>
        </method>

        <method name="operator=">
          <type>recursive_wrapper &amp;</type>

          <parameter name="rhs">
            <paramtype>const T &amp;</paramtype>
          </parameter>

          <purpose>Value assignment operator.</purpose>
          <description>
            <simpara>Assigns <code>rhs</code> into the content of
              <code>*this</code>.</simpara>
          </description>

          <requires>
            <simpara><code>T</code> must fulfill the requirements of the
              <conceptname>Assignable</conceptname>
              concept.</simpara>
          </requires>

          <throws>
            <simpara>May fail with any exceptions arising from the assignment
              operator of <code>T</code>.</simpara>
          </throws>
        </method>

      </method-group>

      <method-group name="queries">

        <overloaded-method name="get">
          <signature>
            <type>T &amp;</type>
          </signature>
          <signature cv="const">
            <type>const T &amp;</type>
          </signature>

          <description>
            <simpara>Returns a reference to the content of
              <code>*this</code>.</simpara>
          </description>

          <throws>Will not throw.</throws>
        </overloaded-method>

        <overloaded-method name="get_pointer">
          <signature>
            <type>T *</type>
          </signature>
          <signature cv="const">
            <type>const T *</type>
          </signature>

          <description>
            <simpara>Returns a pointer to the content of
              <code>*this</code>.</simpara>
          </description>

          <throws>Will not throw.</throws>
        </overloaded-method>

      </method-group>

    </class>
    
    <class name="is_recursive_wrapper">
      <purpose>
        <simpara>Determines whether the specified type is a specialization of
          <code>recursive_wrapper</code>.</simpara>
      </purpose>

      <template>
        <template-type-parameter name="T"/>
      </template>

      <description>
        <simpara>Value is true iff <code>T</code> is a specialization of
          <code><classname>recursive_wrapper</classname></code>.</simpara>
        <simpara><emphasis role="bold">Note</emphasis>:
          <code>is_recursive_wrapper</code> is a model of
          <libraryname>MPL</libraryname>'s
          <emphasis>IntegralConstant</emphasis> concept.</simpara>
      </description>

      <typedef name="type">
        <type><emphasis>unspecified</emphasis></type>
      </typedef>

      <static-constant name="value">
        <type>bool</type>
        <default><emphasis>unspecified</emphasis></default>
      </static-constant>
    </class>

    <class name="unwrap_recursive_wrapper">
      <purpose>
        <simpara>Unwraps the specified argument if given a specialization of
          <code><classname>recursive_wrapper</classname></code>.</simpara>
      </purpose>

      <template>
        <template-type-parameter name="T"/>
      </template>

      <description>
        <simpara><code>type</code> is equivalent to <code>T::type</code> if
          <code>T</code> is a specialization of
          <code><classname>recursive_wrapper</classname></code>. Otherwise,
          <code>type</code> is equivalent to <code>T</code>.</simpara>
      </description>

      <typedef name="type">
        <type><emphasis>unspecified</emphasis></type>
      </typedef>
    </class>

  </namespace>
</header>