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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/context/default.hpp">
- <namespace name="boost">
- <namespace name="proto">
- <namespace name="context">
- <struct name="default_eval">
- <template>
- <template-type-parameter name="Expr"/>
- <template-type-parameter name="Context"/>
- </template>
- <purpose>
- A BinaryFunction that accepts a Proto expression and a context, evaluates
- each child expression with the context, and combines the result using the
- standard C++ meaning for the operator represented by the current expression
- node.
- </purpose>
- <description>
- <para>
- Let <computeroutput><computeroutput>OP</computeroutput></computeroutput> be the C++ operator
- corresponding to <computeroutput>Expr::proto_tag</computeroutput>. (For example, if
- <computeroutput>Tag</computeroutput> is <computeroutput>
- <classname>proto::tag::plus</classname></computeroutput>, let <computeroutput>
- <computeroutput>OP</computeroutput></computeroutput> be <computeroutput>+</computeroutput>.)
- </para>
- <para>
- The behavior of this class is specified in terms of the C++0x <computeroutput>decltype</computeroutput>
- keyword. In systems where this keyword is not available, Proto uses the Boost.Typeof library to
- approximate the behavior.
- </para>
- </description>
- <typedef name="Tag">
- <purpose>For exposition only</purpose>
- <type>typename Expr::tag_type</type>
- </typedef>
- <data-member name="s_expr" specifiers="static">
- <purpose>For exposition only</purpose>
- <type>Expr &</type>
- </data-member>
- <data-member name="s_context" specifiers="static">
- <purpose>For exposition only</purpose>
- <type>Context &</type>
- </data-member>
- <typedef name="result_type">
- <type><emphasis>see-below</emphasis></type>
- <description>
- <itemizedlist>
- <listitem>
- <para>
- If <computeroutput>Tag</computeroutput> corresponds to a unary prefix operator,
- then the result type is
- <programlisting>decltype(
- OP <functionname>proto::eval</functionname>(<functionname>proto::child</functionname>(s_expr), s_context)
- )</programlisting>
- </para>
- </listitem>
- <listitem>
- <para>
- If <computeroutput>Tag</computeroutput> corresponds to a unary postfix operator,
- then the result type is
- <programlisting>decltype(
- <functionname>proto::eval</functionname>(<functionname>proto::child</functionname>(s_expr), s_context) OP
- )</programlisting>
- </para>
- </listitem>
- <listitem>
- <para>
- If <computeroutput>Tag</computeroutput> corresponds to a binary infix operator,
- then the result type is
- <programlisting>decltype(
- <functionname>proto::eval</functionname>(<functionname>proto::left</functionname>(s_expr), s_context) OP
- <functionname>proto::eval</functionname>(<functionname>proto::right</functionname>(s_expr), s_context)
- )</programlisting>
- </para>
- </listitem>
- <listitem>
- <para>
- If <computeroutput>Tag</computeroutput> is <computeroutput>
- <classname>proto::tag::subscript</classname>
- </computeroutput>,
- then the result type is
- <programlisting>decltype(
- <functionname>proto::eval</functionname>(<functionname>proto::left</functionname>(s_expr), s_context) [
- <functionname>proto::eval</functionname>(<functionname>proto::right</functionname>(s_expr), s_context) ]
- )</programlisting>
- </para>
- </listitem>
- <listitem>
- <para>
- If <computeroutput>Tag</computeroutput> is <computeroutput>
- <classname>proto::tag::if_else_</classname>
- </computeroutput>,
- then the result type is
- <programlisting>decltype(
- <functionname>proto::eval</functionname>(<functionname>proto::child_c</functionname><0>(s_expr), s_context) ?
- <functionname>proto::eval</functionname>(<functionname>proto::child_c</functionname><1>(s_expr), s_context) :
- <functionname>proto::eval</functionname>(<functionname>proto::child_c</functionname><2>(s_expr), s_context)
- )</programlisting>
- </para>
- </listitem>
- <listitem>
- <para>
- If <computeroutput>Tag</computeroutput> is <computeroutput>
- <classname>proto::tag::function</classname>
- </computeroutput>,
- then the result type is
- <programlisting>decltype(
- <functionname>proto::eval</functionname>(<functionname>proto::child_c</functionname><0>(s_expr), s_context) (
- <functionname>proto::eval</functionname>(<functionname>proto::child_c</functionname><1>(s_expr), s_context),
- ...
- <functionname>proto::eval</functionname>(<functionname>proto::child_c</functionname><N>(s_expr), s_context) )
- )</programlisting>
- </para>
- </listitem>
- </itemizedlist>
- </description>
- </typedef>
- <method-group name="public member functions">
- <method name="operator()" cv="const">
- <type>result_type</type>
- <parameter name="expr">
- <paramtype>Expr &</paramtype>
- <description>
- <para>The current expression </para>
- </description>
- </parameter>
- <parameter name="context">
- <paramtype>Context &</paramtype>
- <description>
- <para>The evaluation context </para>
- </description>
- </parameter>
- <description>
- <itemizedlist>
- <listitem>
- <para>
- If <computeroutput>Tag</computeroutput> corresponds to a unary prefix operator,
- then return
- <programlisting>OP <functionname>proto::eval</functionname>(<functionname>proto::child</functionname>(expr), context)</programlisting>
- </para>
- </listitem>
- <listitem>
- <para>
- If <computeroutput>Tag</computeroutput> corresponds to a unary postfix operator,
- then return
- <programlisting><functionname>proto::eval</functionname>(<functionname>proto::child</functionname>(expr), context) OP</programlisting>
- </para>
- </listitem>
- <listitem>
- <para>
- If <computeroutput>Tag</computeroutput> corresponds to a binary infix operator,
- then return
- <programlisting><functionname>proto::eval</functionname>(<functionname>proto::left</functionname>(expr), context) OP
- <functionname>proto::eval</functionname>(<functionname>proto::right</functionname>(expr), context)</programlisting>
- </para>
- </listitem>
- <listitem>
- <para>
- If <computeroutput>Tag</computeroutput> is <computeroutput>
- <classname>proto::tag::subscript</classname>
- </computeroutput>,
- then return
- <programlisting><functionname>proto::eval</functionname>(<functionname>proto::left</functionname>(expr), context) [
- <functionname>proto::eval</functionname>(<functionname>proto::right</functionname>(expr), context) ]</programlisting>
- </para>
- </listitem>
- <listitem>
- <para>
- If <computeroutput>Tag</computeroutput> is <computeroutput>
- <classname>proto::tag::if_else_</classname>
- </computeroutput>,
- then return
- <programlisting><functionname>proto::eval</functionname>(<functionname>proto::child_c</functionname><0>(expr), context) ?
- <functionname>proto::eval</functionname>(<functionname>proto::child_c</functionname><1>(expr), context) :
- <functionname>proto::eval</functionname>(<functionname>proto::child_c</functionname><2>(expr), context)</programlisting>
- </para>
- </listitem>
- <listitem>
- <para>
- If <computeroutput>Tag</computeroutput> is <computeroutput>
- <classname>proto::tag::function</classname>
- </computeroutput>,
- then return
- <programlisting><functionname>proto::eval</functionname>(<functionname>proto::child_c</functionname><0>(expr), context) (
- <functionname>proto::eval</functionname>(<functionname>proto::child_c</functionname><1>(expr), context),
- ...
- <functionname>proto::eval</functionname>(<functionname>proto::child_c</functionname><N>(expr), context) )</programlisting>
- </para>
- </listitem>
- </itemizedlist>
- </description>
- </method>
- </method-group>
- </struct>
- <struct name="default_context">
- <purpose>An evaluation context that gives the operators their normal C++ semantics.</purpose>
- <description>
- <para>An evaluation context that gives the operators their normal C++ semantics.</para>
- </description>
- <struct name="eval">
- <template>
- <template-type-parameter name="Expr"/>
- <template-type-parameter name="ThisContext">
- <default>default_context const</default>
- </template-type-parameter>
- </template>
- <inherit><classname>proto::context::default_eval</classname>< Expr, ThisContext ></inherit>
- </struct>
- </struct>
- </namespace>
- </namespace>
- </namespace>
- </header>
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