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- <?xml version="1.0" encoding="utf-8"?>
- <!--
- Copyright 2012 Eric Niebler
- 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/proto/transform/lazy.hpp">
- <para>
- Contains definition of the
- <computeroutput>
- <classname alt="boost::proto::lazy">proto::lazy<></classname>
- </computeroutput> transform.
- </para>
- <namespace name="boost">
- <namespace name="proto">
- <struct name="lazy">
- <template>
- <template-type-parameter name="T"/>
- </template>
- <inherit><classname>proto::transform</classname>< lazy<T> ></inherit>
- <purpose>A <conceptname>PrimitiveTransform</conceptname> that uses
- <computeroutput><classname>proto::make<></classname></computeroutput> to build a
- <conceptname>CallableTransform</conceptname>, and then uses
- <computeroutput><classname>proto::call<></classname></computeroutput> to apply it.
- </purpose>
- <description>
- <para>
- <computeroutput>proto::lazy<></computeroutput> is useful as a higher-order transform,
- when the transform to be applied depends on the current state of the transformation. The
- invocation of the <computeroutput>
- <classname>proto::make<></classname>
- </computeroutput> transform evaluates any nested transforms, and the resulting type is treated
- as a <conceptname>CallableTransform</conceptname>, which is evaluated with
- <computeroutput><classname>proto::call<></classname></computeroutput>.
- </para>
- <para>
- For the full description of the behavior of the
- <computeroutput>
- <classname>proto::lazy<></classname>
- </computeroutput>
- transform, see the documentation for the nested
- <computeroutput>
- <classname>proto::lazy::impl<></classname>
- </computeroutput>
- class template.
- </para>
- </description>
- <struct name="impl">
- <template>
- <template-type-parameter name="Expr"/>
- <template-type-parameter name="State"/>
- <template-type-parameter name="Data"/>
- </template>
- <inherit><type><classname>proto::transform_impl</classname><Expr, State, Data></type></inherit>
- <typedef name="result_type">
- <type><replaceable>see-below</replaceable></type>
- <description>
- <para>
- <computeroutput><classname>proto::lazy</classname><T>::impl<Expr,State,Data>::result_type</computeroutput>
- is calculated as follows:
- <itemizedlist>
- <listitem>
- <para>
- If <computeroutput>T</computeroutput> if of the form
- <computeroutput>O(A<subscript>0</subscript>,…A<subscript>n</subscript>)</computeroutput>, then let <computeroutput>O'</computeroutput>
- be <computeroutput>boost::result_of<<classname>proto::make</classname><O>(Expr, State, Data)>::type</computeroutput>
- and let <computeroutput>T'</computeroutput> be <computeroutput>O'(A<subscript>0</subscript>,…A<subscript>n</subscript>)</computeroutput>.
- </para>
- </listitem>
- <listitem>
- <para>
- If <computeroutput>T</computeroutput> if of the form
- <computeroutput>O(A<subscript>0</subscript>,…A<subscript>n</subscript> ...)</computeroutput>, then let <computeroutput>O'</computeroutput>
- be <computeroutput>boost::result_of<<classname>proto::make</classname><O>(Expr, State, Data)>::type</computeroutput>
- and let <computeroutput>T'</computeroutput> be <computeroutput>O'(A<subscript>0</subscript>,…A<subscript>n</subscript> ...)</computeroutput>.
- </para>
- </listitem>
- <listitem>
- <para>
- Otherwise, let <computeroutput>T'</computeroutput>
- be <computeroutput>boost::result_of<<classname>proto::make</classname><T>(Expr, State, Data)>::type</computeroutput>.
- </para>
- </listitem>
- </itemizedlist>
- <para>
- The result type is
- <computeroutput>
- boost::result_of<<classname>proto::call</classname><T'>(Expr, State, Data)>::type
- </computeroutput>.
- </para>
- </para>
- </description>
- </typedef>
- <method-group name="public member functions">
- <method name="operator()" cv="const">
- <type>result_type</type>
- <parameter name="expr">
- <paramtype>typename impl::expr_param</paramtype>
- </parameter>
- <parameter name="state">
- <paramtype>typename impl::state_param</paramtype>
- </parameter>
- <parameter name="data">
- <paramtype>typename impl::data_param</paramtype>
- </parameter>
- <description>
- <para>
- <computeroutput><classname>proto::lazy</classname><T>::impl<Expr,State,Data>::operator()</computeroutput> behaves as follows:
- <itemizedlist>
- <listitem>
- <para>
- If <computeroutput>T</computeroutput> if of the form
- <computeroutput>O(A<subscript>0</subscript>,…A<subscript>n</subscript>)</computeroutput>, then let <computeroutput>O'</computeroutput>
- be <computeroutput>boost::result_of<<classname>proto::make</classname><O>(Expr, State, Data)>::type</computeroutput>
- and let <computeroutput>T'</computeroutput> be <computeroutput>O'(A<subscript>0</subscript>,…A<subscript>n</subscript>)</computeroutput>.
- </para>
- </listitem>
- <listitem>
- <para>
- If <computeroutput>T</computeroutput> if of the form
- <computeroutput>O(A<subscript>0</subscript>,…A<subscript>n</subscript> ...)</computeroutput>, then let <computeroutput>O'</computeroutput>
- be <computeroutput>boost::result_of<<classname>proto::make</classname><O>(Expr, State, Data)>::type</computeroutput>
- and let <computeroutput>T'</computeroutput> be <computeroutput>O'(A<subscript>0</subscript>,…A<subscript>n</subscript> ...)</computeroutput>.
- </para>
- </listitem>
- <listitem>
- <para>
- Otherwise, let <computeroutput>T'</computeroutput>
- be <computeroutput>boost::result_of<<classname>proto::make</classname><T>(Expr, State, Data)>::type</computeroutput>.
- </para>
- </listitem>
- </itemizedlist>
- </para>
- </description>
- <returns>
- <para>
- <computeroutput>
- <classname>proto::call</classname><T'>()(expr, state, data)
- </computeroutput>
- </para>
- </returns>
- </method>
- </method-group>
- </struct>
- </struct>
- </namespace>
- </namespace>
- </header>
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