1<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd"> 2<html> 3<head> 4<meta http-equiv="Content-Type" content="text/html; charset=UTF-8"> 5<title>Appendices</title> 6<link rel="stylesheet" href="../../../doc/src/boostbook.css" type="text/css"> 7<meta name="generator" content="DocBook XSL Stylesheets V1.79.1"> 8<link rel="home" href="../index.html" title="The Boost C++ Libraries BoostBook Documentation Subset"> 9<link rel="up" href="../proto.html" title="Chapter 32. Boost.Proto"> 10<link rel="prev" href="../Transform.html" title="Concept Transform"> 11<link rel="next" href="../boost_random.html" title="Chapter 33. Boost.Random"> 12</head> 13<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"> 14<table cellpadding="2" width="100%"><tr> 15<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../boost.png"></td> 16<td align="center"><a href="../../../index.html">Home</a></td> 17<td align="center"><a href="../../../libs/libraries.htm">Libraries</a></td> 18<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td> 19<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td> 20<td align="center"><a href="../../../more/index.htm">More</a></td> 21</tr></table> 22<hr> 23<div class="spirit-nav"> 24<a accesskey="p" href="../Transform.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../proto.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../boost_random.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 25</div> 26<div class="section"> 27<div class="titlepage"><div><div><h2 class="title" style="clear: both"> 28<a name="proto.appendices"></a><a class="link" href="appendices.html" title="Appendices">Appendices</a> 29</h2></div></div></div> 30<div class="toc"><dl class="toc"> 31<dt><span class="section"><a href="appendices.html#boost_proto.appendices.release_notes">Appendix A: Release 32 Notes</a></span></dt> 33<dt><span class="section"><a href="appendices.html#boost_proto.appendices.history">Appendix B: History</a></span></dt> 34<dt><span class="section"><a href="appendices.html#boost_proto.appendices.rationale">Appendix C: Rationale</a></span></dt> 35<dt><span class="section"><a href="appendices.html#boost_proto.appendices.implementation">Appendix D: Implementation 36 Notes</a></span></dt> 37<dt><span class="section"><a href="appendices.html#boost_proto.appendices.acknowledgements">Appendix E: 38 Acknowledgements</a></span></dt> 39</dl></div> 40<div class="section"> 41<div class="titlepage"><div><div><h3 class="title"> 42<a name="boost_proto.appendices.release_notes"></a><a class="link" href="appendices.html#boost_proto.appendices.release_notes" title="Appendix A: Release Notes">Appendix A: Release 43 Notes</a> 44</h3></div></div></div> 45<h5> 46<a name="boost_proto.appendices.release_notes.h0"></a> 47 <span class="phrase"><a name="boost_proto.appendices.release_notes.boost_1_51"></a></span><a class="link" href="appendices.html#boost_proto.appendices.release_notes.boost_1_51">Boost 48 1.51</a> 49 </h5> 50<p> 51 <span class="bold"><strong>Unpacking Expressions</strong></span> 52 </p> 53<p> 54 In Boost 1.51, Proto got simple unpacking patterns. When working with Proto 55 transforms, unpacking expressions are useful for unpacking the children of 56 an expression into a function call or an object constructor, while optionally 57 applying some transformations to each child in turn. 58 </p> 59<p> 60 See the <a class="link" href="users_guide.html#boost_proto.users_guide.back_end.expression_transformation.unpacking_expressions" title="Unpacking Expressions">Unpacking 61 Expressions</a> section for more information. 62 </p> 63<h5> 64<a name="boost_proto.appendices.release_notes.h1"></a> 65 <span class="phrase"><a name="boost_proto.appendices.release_notes.boost_1_44"></a></span><a class="link" href="appendices.html#boost_proto.appendices.release_notes.boost_1_44">Boost 66 1.44</a> 67 </h5> 68<p> 69 <span class="bold"><strong>Behavior Change: proto::and_<></strong></span> 70 </p> 71<p> 72 In Boost 1.44, the behavior of <code class="computeroutput"><a class="link" href="../boost/proto/and_.html" title="Struct template and_">proto::and_<></a></code> 73 as a transform changed. Previously, it only applied the transform associated 74 with the last grammar in the set. Now, it applies all the transforms but 75 only returns the result of the last. That makes it behave like C++'s comma 76 operator. For example, a grammar such as: 77 </p> 78<pre class="programlisting"><span class="identifier">proto</span><span class="special">::</span><span class="identifier">and_</span><span class="special"><</span> <span class="identifier">G0</span><span class="special">,</span> <span class="identifier">G1</span><span class="special">,</span> <span class="identifier">G2</span> <span class="special">></span> 79</pre> 80<p> 81 when evaluated with an expression <code class="computeroutput"><span class="identifier">e</span></code> 82 now behaves like this: 83 </p> 84<pre class="programlisting"><span class="special">((</span><span class="keyword">void</span><span class="special">)</span><span class="identifier">G0</span><span class="special">()(</span><span class="identifier">e</span><span class="special">),</span> <span class="special">(</span><span class="keyword">void</span><span class="special">)</span><span class="identifier">G1</span><span class="special">()(</span><span class="identifier">e</span><span class="special">),</span> <span class="identifier">G2</span><span class="special">()(</span><span class="identifier">e</span><span class="special">))</span> 85</pre> 86<div class="note"><table border="0" summary="Note"> 87<tr> 88<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../doc/src/images/note.png"></td> 89<th align="left">Note</th> 90</tr> 91<tr><td align="left" valign="top"><p> 92 Why the void casts? It's to avoid argument-dependent lookup, which might 93 find an overloaded comma operator. 94 </p></td></tr> 95</table></div> 96<p> 97 <span class="bold"><strong>Behavior Change: proto::as_expr() and proto::as_child()</strong></span> 98 </p> 99<p> 100 The functions <code class="computeroutput"><a class="link" href="../boost/proto/as_expr.html" title="Function as_expr">proto::as_expr()</a></code> and <code class="computeroutput"><a class="link" href="../boost/proto/as_child.html" title="Function as_child">proto::as_child()</a></code> 101 are used to guarantee that an object is a Proto expression by turning it 102 into one if it is not already, using an optionally specified domain. In previous 103 releases, when these functions were passed a Proto expression in a domain 104 different to the one specified, they would apply the specified domain's generator, 105 resulting in a twice-wrapped expression. This behavior was surprising to 106 some users. 107 </p> 108<p> 109 The new behavior of these two functions is to always leave Proto expressions 110 alone, regardless of the expressions' domains. 111 </p> 112<p> 113 <span class="bold"><strong>Behavior Change: proto::(pod_)generator<> and 114 proto::basic_expr<></strong></span> 115 </p> 116<p> 117 Users familiar with Proto's extension mechanism have probably used either 118 <code class="computeroutput"><a class="link" href="../boost/proto/generator.html" title="Struct template generator">proto::generator<></a></code> or <code class="computeroutput"><a class="link" href="../boost/proto/pod_generator.html" title="Struct template pod_generator">proto::pod_generator<></a></code> 119 with a wrapper template when defining their domain. In the past, Proto would 120 instantiate your wrapper template with instances of <code class="computeroutput"><a class="link" href="../boost/proto/expr.html" title="Struct template expr">proto::expr<></a></code>. 121 In Boost 1.44, Proto now instantiates your wrapper template with instances 122 of a new type: <code class="computeroutput"><a class="link" href="../boost/proto/basic_expr.html" title="Struct template basic_expr">proto::basic_expr<></a></code>. 123 </p> 124<p> 125 For instance: 126 </p> 127<pre class="programlisting"><span class="comment">// An expression wrapper</span> 128<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Expr</span><span class="special">></span> 129<span class="keyword">struct</span> <span class="identifier">my_expr_wrapper</span><span class="special">;</span> 130 131<span class="comment">// A domain</span> 132<span class="keyword">struct</span> <span class="identifier">my_domain</span> 133 <span class="special">:</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">domain</span><span class="special"><</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">generator</span><span class="special"><</span> <span class="identifier">my_expr_wrapper</span> <span class="special">></span> <span class="special">></span> 134<span class="special">{};</span> 135 136<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Expr</span><span class="special">></span> 137<span class="keyword">struct</span> <span class="identifier">my_expr_wrapper</span> 138 <span class="special">:</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">extends</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">my_expr_wrapper</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">>,</span> <span class="identifier">my_domain</span><span class="special">></span> 139<span class="special">{</span> 140 <span class="comment">// Before 1.44, Expr was an instance of proto::expr<></span> 141 <span class="comment">// In 1.44, Expr is an instance of proto::basic_expr<></span> 142<span class="special">};</span> 143</pre> 144<p> 145 The motivation for this change was to improve compile times. <code class="computeroutput"><a class="link" href="../boost/proto/expr.html" title="Struct template expr">proto::expr<></a></code> 146 is an expensive type to instantiate because it defines a host of member functions. 147 When defining your own expression wrapper, the instance of <code class="computeroutput"><a class="link" href="../boost/proto/expr.html" title="Struct template expr">proto::expr<></a></code> 148 sits as a hidden data member function in your wrapper and the members of 149 <code class="computeroutput"><a class="link" href="../boost/proto/expr.html" title="Struct template expr">proto::expr<></a></code> go unused. Therefore, 150 the cost of those member functions is wasted. In contrast, <code class="computeroutput"><a class="link" href="../boost/proto/basic_expr.html" title="Struct template basic_expr">proto::basic_expr<></a></code> 151 is a very lightweight type with no member functions at all. 152 </p> 153<p> 154 The vast majority of programs should recompile without any source changes. 155 However, if somewhere you are assuming that you will be given instances specifically 156 of <code class="computeroutput"><a class="link" href="../boost/proto/expr.html" title="Struct template expr">proto::expr<></a></code>, your code will break. 157 </p> 158<p> 159 <span class="bold"><strong>New Feature: Sub-domains</strong></span> 160 </p> 161<p> 162 In Boost 1.44, Proto introduces an important new feature called "sub-domains". 163 This gives you a way to spcify that one domain is compatible with another 164 such that expressions in one domain can be freely mixed with expressions 165 in another. You can define one domain to be the sub-domain of another by 166 using the third template parameter of <code class="computeroutput"><a class="link" href="../boost/proto/domain.html" title="Struct template domain">proto::domain<></a></code>. 167 </p> 168<p> 169 For instance: 170 </p> 171<pre class="programlisting"><span class="comment">// Not shown: define some expression</span> 172<span class="comment">// generators genA and genB</span> 173 174<span class="keyword">struct</span> <span class="identifier">A</span> 175 <span class="special">:</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">domain</span><span class="special"><</span> <span class="identifier">genA</span><span class="special">,</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">_</span> <span class="special">></span> 176<span class="special">{};</span> 177 178<span class="comment">// Define a domain B that is the sub-domain</span> 179<span class="comment">// of domain A.</span> 180<span class="keyword">struct</span> <span class="identifier">B</span> 181 <span class="special">:</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">domain</span><span class="special"><</span> <span class="identifier">genB</span><span class="special">,</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">_</span><span class="special">,</span> <span class="identifier">A</span> <span class="special">></span> 182<span class="special">{};</span> 183</pre> 184<p> 185 Expressions in domains <code class="computeroutput"><span class="identifier">A</span></code> 186 and <code class="computeroutput"><span class="identifier">B</span></code> can have different 187 wrappers (hence, different interfaces), but they can be combined into larger 188 expressions. Without a sub-domain relationship, this would have been an error. 189 The domain of the resulting expression in this case would be <code class="computeroutput"><span class="identifier">A</span></code>. 190 </p> 191<p> 192 The complete description of sub-domains can be found in the reference sections 193 for <code class="computeroutput"><a class="link" href="../boost/proto/domain.html" title="Struct template domain">proto::domain<></a></code> and <code class="computeroutput"><a class="link" href="../boost/proto/deduce_domain.html" title="Struct deduce_domain">proto::deduce_domain</a></code>. 194 </p> 195<p> 196 <span class="bold"><strong>New Feature: Domain-specific as_expr() and as_child()</strong></span> 197 </p> 198<p> 199 Proto has always allowed users to customize expressions post-hoc by specifying 200 a Generator when defining their domain. But it has never allowed users to 201 control how Proto assembles sub-expressions in the first place. As of Boost 202 1.44, users now have this power. 203 </p> 204<p> 205 Users defining their own domain can now specify how <code class="computeroutput"><a class="link" href="../boost/proto/as_expr.html" title="Function as_expr">proto::as_expr()</a></code> 206 and <code class="computeroutput"><a class="link" href="../boost/proto/as_child.html" title="Function as_child">proto::as_child()</a></code> work in their domain. They 207 can do this easily by defining nested class templates named <code class="computeroutput"><span class="identifier">as_expr</span></code> and/or <code class="computeroutput"><span class="identifier">as_child</span></code> 208 within their domain class. 209 </p> 210<p> 211 For example: 212 </p> 213<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">my_domain</span> 214 <span class="special">:</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">domain</span><span class="special"><</span> <span class="identifier">my_generator</span> <span class="special">></span> 215<span class="special">{</span> 216 <span class="keyword">typedef</span> 217 <span class="identifier">proto</span><span class="special">::</span><span class="identifier">domain</span><span class="special"><</span> <span class="identifier">my_generator</span> <span class="special">></span> 218 <span class="identifier">base_domain</span><span class="special">;</span> 219 220 <span class="comment">// For my_domain, as_child does the same as</span> 221 <span class="comment">// what as_expr does by default.</span> 222 <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> 223 <span class="keyword">struct</span> <span class="identifier">as_child</span> 224 <span class="special">:</span> <span class="identifier">base_domain</span><span class="special">::</span><span class="identifier">as_expr</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> 225 <span class="special">{};</span> 226<span class="special">};</span> 227</pre> 228<p> 229 In the above example, <code class="computeroutput"><span class="identifier">my_domain</span><span class="special">::</span><span class="identifier">as_child</span><span class="special"><></span></code> simply defers to <code class="computeroutput"><span class="identifier">proto</span><span class="special">::</span><span class="identifier">domain</span><span class="special">::</span><span class="identifier">as_expr</span><span class="special"><></span></code>. This has the nice effect of causing 230 all terminals to be captured by value instead of by reference, and to likewise 231 store child expressions by value. The result is that expressions in <code class="computeroutput"><span class="identifier">my_domain</span></code> are safe to store in <code class="computeroutput"><span class="keyword">auto</span></code> variables because they will not have 232 dangling references to intermediate temporary expressions. (Naturally, it 233 also means that expression construction has extra runtime overhead of copying 234 that the compiler may or may not be able to optimize away.) 235 </p> 236<h5> 237<a name="boost_proto.appendices.release_notes.h2"></a> 238 <span class="phrase"><a name="boost_proto.appendices.release_notes.boost_1_43"></a></span><a class="link" href="appendices.html#boost_proto.appendices.release_notes.boost_1_43">Boost 239 1.43</a> 240 </h5> 241<p> 242 In Boost 1.43, the recommended usage of <code class="computeroutput"><a class="link" href="../boost/proto/extends.html" title="Struct template extends">proto::extends<></a></code> 243 changed slightly. The new usage looks like this: 244 </p> 245<pre class="programlisting"><span class="comment">// my_expr is an expression extension of the Expr parameter</span> 246<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Expr</span><span class="special">></span> 247<span class="keyword">struct</span> <span class="identifier">my_expr</span> 248 <span class="special">:</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">extends</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">my_expr</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">>,</span> <span class="identifier">my_domain</span><span class="special">></span> 249<span class="special">{</span> 250 <span class="identifier">my_expr</span><span class="special">(</span><span class="identifier">Expr</span> <span class="keyword">const</span> <span class="special">&</span><span class="identifier">expr</span> <span class="special">=</span> <span class="identifier">Expr</span><span class="special">())</span> 251 <span class="special">:</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">extends</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">my_expr</span><span class="special">,</span> <span class="identifier">my_domain</span><span class="special">>(</span><span class="identifier">expr</span><span class="special">)</span> 252 <span class="special">{}</span> 253 254 <span class="comment">// NEW: use the following macro to bring</span> 255 <span class="comment">// proto::extends::operator= into scope.</span> 256 <span class="identifier">BOOST_PROTO_EXTENDS_USING_ASSIGN</span><span class="special">(</span><span class="identifier">my_expr</span><span class="special">)</span> 257<span class="special">};</span> 258</pre> 259<p> 260 The new thing is the use of the <code class="literal"><code class="computeroutput"><a class="link" href="../BOOST_PROTO__1_3_33_5_10_8.html" title="Macro BOOST_PROTO_EXTENDS_USING_ASSIGN">BOOST_PROTO_EXTENDS_USING_ASSIGN</a></code>()</code> 261 macro. To allow assignment operators to build expression trees, <code class="computeroutput"><a class="link" href="../boost/proto/extends.html" title="Struct template extends">proto::extends<></a></code> overloads the assignment 262 operator. However, for the <code class="computeroutput"><span class="identifier">my_expr</span></code> 263 template, the compiler generates a default copy assignment operator that 264 hides the ones in <code class="computeroutput"><a class="link" href="../boost/proto/extends.html" title="Struct template extends">proto::extends<></a></code>. This is often not desired 265 (although it depends on the syntax you want to allow). 266 </p> 267<p> 268 Previously, the recommended usage was to do this: 269 </p> 270<pre class="programlisting"><span class="comment">// my_expr is an expression extension of the Expr parameter</span> 271<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Expr</span><span class="special">></span> 272<span class="keyword">struct</span> <span class="identifier">my_expr</span> 273 <span class="special">:</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">extends</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">my_expr</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">>,</span> <span class="identifier">my_domain</span><span class="special">></span> 274<span class="special">{</span> 275 <span class="identifier">my_expr</span><span class="special">(</span><span class="identifier">Expr</span> <span class="keyword">const</span> <span class="special">&</span><span class="identifier">expr</span> <span class="special">=</span> <span class="identifier">Expr</span><span class="special">())</span> 276 <span class="special">:</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">extends</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">my_expr</span><span class="special">,</span> <span class="identifier">my_domain</span><span class="special">>(</span><span class="identifier">expr</span><span class="special">)</span> 277 <span class="special">{}</span> 278 279 <span class="comment">// OLD: don't do it like this anymore.</span> 280 <span class="keyword">using</span> <span class="identifier">proto</span><span class="special">::</span><span class="identifier">extends</span><span class="special"><</span><span class="identifier">Expr</span><span class="special">,</span> <span class="identifier">my_expr</span><span class="special">,</span> <span class="identifier">my_domain</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=;</span> 281<span class="special">};</span> 282</pre> 283<p> 284 While this works in the majority of cases, it still doesn't suppress the 285 implicit generation of the default assignment operator. As a result, expressions 286 of the form <code class="computeroutput"><span class="identifier">a</span> <span class="special">=</span> 287 <span class="identifier">b</span></code> could either build an expression 288 template or do a copy assignment depending on whether the types of <code class="computeroutput"><span class="identifier">a</span></code> and <code class="computeroutput"><span class="identifier">b</span></code> 289 happen to be the same. That can lead to subtle bugs, so the behavior was 290 changed. 291 </p> 292<p> 293 The <code class="literal"><code class="computeroutput"><a class="link" href="../BOOST_PROTO__1_3_33_5_10_8.html" title="Macro BOOST_PROTO_EXTENDS_USING_ASSIGN">BOOST_PROTO_EXTENDS_USING_ASSIGN</a></code>()</code> 294 brings into scope the assignment operators defined in <code class="computeroutput"><a class="link" href="../boost/proto/extends.html" title="Struct template extends">proto::extends<></a></code> 295 as well as suppresses the generation of the copy assignment operator. 296 </p> 297<p> 298 Also note that the <code class="computeroutput"><a class="link" href="../boost/proto/literal.html" title="Struct template literal">proto::literal<></a></code> class template, which 299 uses <code class="computeroutput"><a class="link" href="../boost/proto/extends.html" title="Struct template extends">proto::extends<></a></code>, has been chaged to use 300 <code class="literal"><code class="computeroutput"><a class="link" href="../BOOST_PROTO__1_3_33_5_10_8.html" title="Macro BOOST_PROTO_EXTENDS_USING_ASSIGN">BOOST_PROTO_EXTENDS_USING_ASSIGN</a></code>()</code>. 301 The implications are highlighted in the sample code below: 302 </p> 303<pre class="programlisting"><span class="identifier">proto</span><span class="special">::</span><span class="identifier">literal</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">a</span><span class="special">(</span><span class="number">1</span><span class="special">),</span> <span class="identifier">b</span><span class="special">(</span><span class="number">2</span><span class="special">);</span> <span class="comment">// two non-const proto literals</span> 304<span class="identifier">proto</span><span class="special">::</span><span class="identifier">literal</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="keyword">const</span> <span class="identifier">c</span><span class="special">(</span><span class="number">3</span><span class="special">);</span> <span class="comment">// a const proto literal</span> 305 306<span class="identifier">a</span> <span class="special">=</span> <span class="identifier">b</span><span class="special">;</span> <span class="comment">// No-op. Builds an expression tree and discards it.</span> 307 <span class="comment">// Same behavior in 1.42 and 1.43.</span> 308 309<span class="identifier">a</span> <span class="special">=</span> <span class="identifier">c</span><span class="special">;</span> <span class="comment">// CHANGE! In 1.42, this performed copy assignment, causing</span> 310 <span class="comment">// a's value to change to 3. In 1.43, the behavior is now</span> 311 <span class="comment">// the same as above: build and discard an expression tree.</span> 312</pre> 313</div> 314<div class="section"> 315<div class="titlepage"><div><div><h3 class="title"> 316<a name="boost_proto.appendices.history"></a><a class="link" href="appendices.html#boost_proto.appendices.history" title="Appendix B: History">Appendix B: History</a> 317</h3></div></div></div> 318<div class="variablelist"> 319<p class="title"><b></b></p> 320<dl class="variablelist"> 321<dt><span class="term">August 13, 2010</span></dt> 322<dd><p> 323 Boost 1.44: Proto gets sub-domains and per-domain control of <code class="computeroutput"><a class="link" href="../boost/proto/as_expr.html" title="Function as_expr">proto::as_expr()</a></code> and <code class="computeroutput"><a class="link" href="../boost/proto/as_child.html" title="Function as_child">proto::as_child()</a></code> to meet the needs 324 of Phoenix3. 325 </p></dd> 326<dt><span class="term">August 11, 2008</span></dt> 327<dd><p> 328 Proto v4 is merged to Boost trunk with more powerful transform protocol. 329 </p></dd> 330<dt><span class="term">April 7, 2008</span></dt> 331<dd><p> 332 Proto is accepted into Boost. 333 </p></dd> 334<dt><span class="term">March 1, 2008</span></dt> 335<dd><p> 336 Proto's Boost review begins. 337 </p></dd> 338<dt><span class="term">January 11, 2008</span></dt> 339<dd><p> 340 Boost.Proto v3 brings separation of grammars and transforms and a "round" 341 lambda syntax for defining transforms in-place. 342 </p></dd> 343<dt><span class="term">April 15, 2007</span></dt> 344<dd><p> 345 Boost.Xpressive is ported from Proto compilers to Proto transforms. 346 Support for old Proto compilers is dropped. 347 </p></dd> 348<dt><span class="term">April 4, 2007</span></dt> 349<dd><p> 350 Preliminary submission of Proto to Boost. 351 </p></dd> 352<dt><span class="term">December 11, 2006</span></dt> 353<dd><p> 354 The idea for transforms that decorate grammar rules is born in a private 355 email discussion with Joel de Guzman and Hartmut Kaiser. The first 356 transforms are committed to CVS 5 days later on December 16. 357 </p></dd> 358<dt><span class="term">November 1, 2006</span></dt> 359<dd><p> 360 The idea for <code class="computeroutput"><span class="identifier">proto</span><span class="special">::</span><span class="identifier">matches</span><span class="special"><></span></code> and the whole grammar facility 361 is hatched during a discussion with Hartmut Kaiser on the spirit-devel 362 list. The first version of <code class="computeroutput"><span class="identifier">proto</span><span class="special">::</span><span class="identifier">matches</span><span class="special"><></span></code> is checked into CVS 3 days 363 later. Message is <a href="http://osdir.com/ml/parsers.spirit.devel/2006-11/msg00003.html" target="_top">here</a>. 364 </p></dd> 365<dt><span class="term">October 28, 2006</span></dt> 366<dd><p> 367 Proto is reborn, this time with a uniform expression types that are 368 POD. Announcement is <a href="http://lists.boost.org/Archives/boost/2006/10/112453.php" target="_top">here</a>. 369 </p></dd> 370<dt><span class="term">April 20, 2005</span></dt> 371<dd><p> 372 Proto is born as a major refactorization of Boost.Xpressive's meta-programming. 373 Proto offers expression types, operator overloads and "compilers", 374 an early formulation of what later became transforms. Announcement 375 is <a href="http://lists.boost.org/Archives/boost/2005/04/85256.php" target="_top">here</a>. 376 </p></dd> 377</dl> 378</div> 379</div> 380<div class="section"> 381<div class="titlepage"><div><div><h3 class="title"> 382<a name="boost_proto.appendices.rationale"></a><a class="link" href="appendices.html#boost_proto.appendices.rationale" title="Appendix C: Rationale">Appendix C: Rationale</a> 383</h3></div></div></div> 384<div class="toc"><dl class="toc"> 385<dt><span class="section"><a href="appendices.html#boost_proto.appendices.rationale.static_initialization">Static 386 Initialization</a></span></dt> 387<dt><span class="section"><a href="appendices.html#boost_proto.appendices.rationale.preprocessor">Why 388 Not Reuse MPL, Fusion, et cetera?</a></span></dt> 389</dl></div> 390<div class="section"> 391<div class="titlepage"><div><div><h4 class="title"> 392<a name="boost_proto.appendices.rationale.static_initialization"></a><a class="link" href="appendices.html#boost_proto.appendices.rationale.static_initialization" title="Static Initialization">Static 393 Initialization</a> 394</h4></div></div></div> 395<p> 396 Proto expression types are PODs (Plain Old Data), and do not have constructors. 397 They are brace-initialized, as follows: 398 </p> 399<pre class="programlisting"><span class="identifier">terminal</span><span class="special"><</span><span class="keyword">int</span><span class="special">>::</span><span class="identifier">type</span> <span class="keyword">const</span> <span class="identifier">_i</span> <span class="special">=</span> <span class="special">{</span><span class="number">1</span><span class="special">};</span> 400</pre> 401<p> 402 The reason is so that expression objects like <code class="computeroutput"><span class="identifier">_i</span></code> 403 above can be <span class="emphasis"><em>statically initialized</em></span>. Why is static 404 initialization important? The terminals of many embedded domain-specific 405 languages are likely to be global const objects, like <code class="computeroutput"><span class="identifier">_1</span></code> 406 and <code class="computeroutput"><span class="identifier">_2</span></code> from the Boost Lambda 407 Library. Were these object to require run-time initialization, it might 408 be possible to use these objects before they are initialized. That would 409 be bad. Statically initialized objects cannot be misused that way. 410 </p> 411</div> 412<div class="section"> 413<div class="titlepage"><div><div><h4 class="title"> 414<a name="boost_proto.appendices.rationale.preprocessor"></a><a class="link" href="appendices.html#boost_proto.appendices.rationale.preprocessor" title="Why Not Reuse MPL, Fusion, et cetera?">Why 415 Not Reuse MPL, Fusion, et cetera?</a> 416</h4></div></div></div> 417<p> 418 Anyone who has peeked at Proto's source code has probably wondered, "Why 419 all the dirty preprocessor gunk? Couldn't this have been all implemented 420 cleanly on top of libraries like MPL and Fusion?" The answer is that 421 Proto could have been implemented this way, and in fact was at one point. 422 The problem is that template metaprogramming (TMP) makes for longer compile 423 times. As a foundation upon which other TMP-heavy libraries will be built, 424 Proto itself should be as lightweight as possible. That is achieved by 425 prefering preprocessor metaprogramming to template metaprogramming. Expanding 426 a macro is far more efficient than instantiating a template. In some cases, 427 the "clean" version takes 10x longer to compile than the "dirty" 428 version. 429 </p> 430<p> 431 The "clean and slow" version of Proto can still be found at http://svn.boost.org/svn/boost/branches/proto/v3. 432 Anyone who is interested can download it and verify that it is, in fact, 433 unusably slow to compile. Note that this branch's development was abandoned, 434 and it does not conform exactly with Proto's current interface. 435 </p> 436</div> 437</div> 438<div class="section"> 439<div class="titlepage"><div><div><h3 class="title"> 440<a name="boost_proto.appendices.implementation"></a><a class="link" href="appendices.html#boost_proto.appendices.implementation" title="Appendix D: Implementation Notes">Appendix D: Implementation 441 Notes</a> 442</h3></div></div></div> 443<div class="toc"><dl class="toc"> 444<dt><span class="section"><a href="appendices.html#boost_proto.appendices.implementation.sfinae">Quick-n-Dirty 445 Type Categorization</a></span></dt> 446<dt><span class="section"><a href="appendices.html#boost_proto.appendices.implementation.function_arity">Detecting 447 the Arity of Function Objects</a></span></dt> 448</dl></div> 449<div class="section"> 450<div class="titlepage"><div><div><h4 class="title"> 451<a name="boost_proto.appendices.implementation.sfinae"></a><a class="link" href="appendices.html#boost_proto.appendices.implementation.sfinae" title="Quick-n-Dirty Type Categorization">Quick-n-Dirty 452 Type Categorization</a> 453</h4></div></div></div> 454<p> 455 Much has already been written about dispatching on type traits using SFINAE 456 (Substitution Failure Is Not An Error) techniques in C++. There is a Boost 457 library, Boost.Enable_if, to make the technique idiomatic. Proto dispatches 458 on type traits extensively, but it doesn't use <code class="computeroutput"><span class="identifier">enable_if</span><span class="special"><></span></code> very often. Rather, it dispatches 459 based on the presence or absence of nested types, often typedefs for void. 460 </p> 461<p> 462 Consider the implementation of <code class="computeroutput"><span class="identifier">is_expr</span><span class="special"><></span></code>. It could have been written as 463 something like this: 464 </p> 465<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span> 466<span class="keyword">struct</span> <span class="identifier">is_expr</span> 467 <span class="special">:</span> <span class="identifier">is_base_and_derived</span><span class="special"><</span><span class="identifier">proto</span><span class="special">::</span><span class="identifier">some_expr_base</span><span class="special">,</span> <span class="identifier">T</span><span class="special">></span> 468<span class="special">{};</span> 469</pre> 470<p> 471 Rather, it is implemented as this: 472 </p> 473<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">Void</span> <span class="special">=</span> <span class="keyword">void</span><span class="special">></span> 474<span class="keyword">struct</span> <span class="identifier">is_expr</span> 475 <span class="special">:</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">false_</span> 476<span class="special">{};</span> 477 478<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span> 479<span class="keyword">struct</span> <span class="identifier">is_expr</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">T</span><span class="special">::</span><span class="identifier">proto_is_expr_</span><span class="special">></span> 480 <span class="special">:</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">true_</span> 481<span class="special">{};</span> 482</pre> 483<p> 484 This relies on the fact that the specialization will be preferred if <code class="computeroutput"><span class="identifier">T</span></code> has a nested <code class="computeroutput"><span class="identifier">proto_is_expr_</span></code> 485 that is a typedef for <code class="computeroutput"><span class="keyword">void</span></code>. 486 All Proto expression types have such a nested typedef. 487 </p> 488<p> 489 Why does Proto do it this way? The reason is because, after running extensive 490 benchmarks while trying to improve compile times, I have found that this 491 approach compiles faster. It requires exactly one template instantiation. 492 The other approach requires at least 2: <code class="computeroutput"><span class="identifier">is_expr</span><span class="special"><></span></code> and <code class="computeroutput"><span class="identifier">is_base_and_derived</span><span class="special"><></span></code>, plus whatever templates <code class="computeroutput"><span class="identifier">is_base_and_derived</span><span class="special"><></span></code> 493 may instantiate. 494 </p> 495</div> 496<div class="section"> 497<div class="titlepage"><div><div><h4 class="title"> 498<a name="boost_proto.appendices.implementation.function_arity"></a><a class="link" href="appendices.html#boost_proto.appendices.implementation.function_arity" title="Detecting the Arity of Function Objects">Detecting 499 the Arity of Function Objects</a> 500</h4></div></div></div> 501<p> 502 In several places, Proto needs to know whether or not a function object 503 <code class="computeroutput"><span class="identifier">Fun</span></code> can be called with 504 certain parameters and take a fallback action if not. This happens in 505 <code class="computeroutput"><a class="link" href="../boost/proto/context/callable_context.html" title="Struct template callable_context">proto::callable_context<></a></code> 506 and in the <code class="computeroutput"><a class="link" href="../boost/proto/call.html" title="Struct template call">proto::call<></a></code> transform. How does 507 Proto know? It involves some tricky metaprogramming. Here's how. 508 </p> 509<p> 510 Another way of framing the question is by trying to implement the following 511 <code class="computeroutput"><span class="identifier">can_be_called</span><span class="special"><></span></code> 512 Boolean metafunction, which checks to see if a function object <code class="computeroutput"><span class="identifier">Fun</span></code> can be called with parameters of 513 type <code class="computeroutput"><span class="identifier">A</span></code> and <code class="computeroutput"><span class="identifier">B</span></code>: 514 </p> 515<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Fun</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">A</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">B</span><span class="special">></span> 516<span class="keyword">struct</span> <span class="identifier">can_be_called</span><span class="special">;</span> 517</pre> 518<p> 519 First, we define the following <code class="computeroutput"><span class="identifier">dont_care</span></code> 520 struct, which has an implicit conversion from anything. And not just any 521 implicit conversion; it has a ellipsis conversion, which is the worst possible 522 conversion for the purposes of overload resolution: 523 </p> 524<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">dont_care</span> 525<span class="special">{</span> 526 <span class="identifier">dont_care</span><span class="special">(...);</span> 527<span class="special">};</span> 528</pre> 529<p> 530 We also need some private type known only to us with an overloaded comma 531 operator (!), and some functions that detect the presence of this type 532 and return types with different sizes, as follows: 533 </p> 534<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">private_type</span> 535<span class="special">{</span> 536 <span class="identifier">private_type</span> <span class="keyword">const</span> <span class="special">&</span><span class="keyword">operator</span><span class="special">,(</span><span class="keyword">int</span><span class="special">)</span> <span class="keyword">const</span><span class="special">;</span> 537<span class="special">};</span> 538 539<span class="keyword">typedef</span> <span class="keyword">char</span> <span class="identifier">yes_type</span><span class="special">;</span> <span class="comment">// sizeof(yes_type) == 1</span> 540<span class="keyword">typedef</span> <span class="keyword">char</span> <span class="special">(&</span><span class="identifier">no_type</span><span class="special">)[</span><span class="number">2</span><span class="special">];</span> <span class="comment">// sizeof(no_type) == 2</span> 541 542<span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span> 543<span class="identifier">no_type</span> <span class="identifier">is_private_type</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span> <span class="special">&);</span> 544 545<span class="identifier">yes_type</span> <span class="identifier">is_private_type</span><span class="special">(</span><span class="identifier">private_type</span> <span class="keyword">const</span> <span class="special">&);</span> 546</pre> 547<p> 548 Next, we implement a binary function object wrapper with a very strange 549 conversion operator, whose meaning will become clear later. 550 </p> 551<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Fun</span><span class="special">></span> 552<span class="keyword">struct</span> <span class="identifier">funwrap2</span> <span class="special">:</span> <span class="identifier">Fun</span> 553<span class="special">{</span> 554 <span class="identifier">funwrap2</span><span class="special">();</span> 555 <span class="keyword">typedef</span> <span class="identifier">private_type</span> <span class="keyword">const</span> <span class="special">&(*</span><span class="identifier">pointer_to_function</span><span class="special">)(</span><span class="identifier">dont_care</span><span class="special">,</span> <span class="identifier">dont_care</span><span class="special">);</span> 556 <span class="keyword">operator</span> <span class="identifier">pointer_to_function</span><span class="special">()</span> <span class="keyword">const</span><span class="special">;</span> 557<span class="special">};</span> 558</pre> 559<p> 560 With all of these bits and pieces, we can implement <code class="computeroutput"><span class="identifier">can_be_called</span><span class="special"><></span></code> as follows: 561 </p> 562<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> <span class="identifier">Fun</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">A</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">B</span><span class="special">></span> 563<span class="keyword">struct</span> <span class="identifier">can_be_called</span> 564<span class="special">{</span> 565 <span class="keyword">static</span> <span class="identifier">funwrap2</span><span class="special"><</span><span class="identifier">Fun</span><span class="special">></span> <span class="special">&</span><span class="identifier">fun</span><span class="special">;</span> 566 <span class="keyword">static</span> <span class="identifier">A</span> <span class="special">&</span><span class="identifier">a</span><span class="special">;</span> 567 <span class="keyword">static</span> <span class="identifier">B</span> <span class="special">&</span><span class="identifier">b</span><span class="special">;</span> 568 569 <span class="keyword">static</span> <span class="keyword">bool</span> <span class="keyword">const</span> <span class="identifier">value</span> <span class="special">=</span> <span class="special">(</span> 570 <span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">no_type</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">is_private_type</span><span class="special">(</span> <span class="special">(</span><span class="identifier">fun</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span><span class="identifier">b</span><span class="special">),</span> <span class="number">0</span><span class="special">)</span> <span class="special">))</span> 571 <span class="special">);</span> 572 573 <span class="keyword">typedef</span> <span class="identifier">mpl</span><span class="special">::</span><span class="identifier">bool_</span><span class="special"><</span><span class="identifier">value</span><span class="special">></span> <span class="identifier">type</span><span class="special">;</span> 574<span class="special">};</span> 575</pre> 576<p> 577 The idea is to make it so that <code class="computeroutput"><span class="identifier">fun</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span><span class="identifier">b</span><span class="special">)</span></code> will 578 always compile by adding our own binary function overload, but doing it 579 in such a way that we can detect whether our overload was selected or not. 580 And we rig it so that our overload is selected if there is really no better 581 option. What follows is a description of how <code class="computeroutput"><span class="identifier">can_be_called</span><span class="special"><></span></code> works. 582 </p> 583<p> 584 We wrap <code class="computeroutput"><span class="identifier">Fun</span></code> in a type that 585 has an implicit conversion to a pointer to a binary function. An object 586 <code class="computeroutput"><span class="identifier">fun</span></code> of class type can be 587 invoked as <code class="computeroutput"><span class="identifier">fun</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">b</span><span class="special">)</span></code> if it has such a conversion operator, 588 but since it involves a user-defined conversion operator, it is less preferred 589 than an overloaded <code class="computeroutput"><span class="keyword">operator</span><span class="special">()</span></code>, which requires no such conversion. 590 </p> 591<p> 592 The function pointer can accept any two arguments by virtue of the <code class="computeroutput"><span class="identifier">dont_care</span></code> type. The conversion sequence 593 for each argument is guaranteed to be the worst possible conversion sequence: 594 an implicit conversion through an ellipsis, and a user-defined conversion 595 to <code class="computeroutput"><span class="identifier">dont_care</span></code>. In total, 596 it means that <code class="computeroutput"><span class="identifier">funwrap2</span><span class="special"><</span><span class="identifier">Fun</span><span class="special">>()(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">b</span><span class="special">)</span></code> 597 will always compile, but it will select our overload only if there really 598 is no better option. 599 </p> 600<p> 601 If there is a better option --- for example if <code class="computeroutput"><span class="identifier">Fun</span></code> 602 has an overloaded function call operator such as <code class="computeroutput"><span class="keyword">void</span> 603 <span class="keyword">operator</span><span class="special">()(</span><span class="identifier">A</span> <span class="identifier">a</span><span class="special">,</span> <span class="identifier">B</span> <span class="identifier">b</span><span class="special">)</span></code> --- 604 then <code class="computeroutput"><span class="identifier">fun</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">b</span><span class="special">)</span></code> will resolve to that one instead. The 605 question now is how to detect which function got picked by overload resolution. 606 </p> 607<p> 608 Notice how <code class="computeroutput"><span class="identifier">fun</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">b</span><span class="special">)</span></code> appears in <code class="computeroutput"><span class="identifier">can_be_called</span><span class="special"><></span></code>: <code class="computeroutput"><span class="special">(</span><span class="identifier">fun</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">b</span><span class="special">),</span> <span class="number">0</span><span class="special">)</span></code>. 609 Why do we use the comma operator there? The reason is because we are using 610 this expression as the argument to a function. If the return type of <code class="computeroutput"><span class="identifier">fun</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span> <span class="identifier">b</span><span class="special">)</span></code> is <code class="computeroutput"><span class="keyword">void</span></code>, 611 it cannot legally be used as an argument to a function. The comma operator 612 sidesteps the issue. 613 </p> 614<p> 615 This should also make plain the purpose of the overloaded comma operator 616 in <code class="computeroutput"><span class="identifier">private_type</span></code>. The return 617 type of the pointer to function is <code class="computeroutput"><span class="identifier">private_type</span></code>. 618 If overload resolution selects our overload, then the type of <code class="computeroutput"><span class="special">(</span><span class="identifier">fun</span><span class="special">(</span><span class="identifier">a</span><span class="special">,</span> 619 <span class="identifier">b</span><span class="special">),</span> 620 <span class="number">0</span><span class="special">)</span></code> 621 is <code class="computeroutput"><span class="identifier">private_type</span></code>. Otherwise, 622 it is <code class="computeroutput"><span class="keyword">int</span></code>. That fact is used 623 to dispatch to either overload of <code class="computeroutput"><span class="identifier">is_private_type</span><span class="special">()</span></code>, which encodes its answer in the size 624 of its return type. 625 </p> 626<p> 627 That's how it works with binary functions. Now repeat the above process 628 for functions up to some predefined function arity, and you're done. 629 </p> 630</div> 631</div> 632<div class="section"> 633<div class="titlepage"><div><div><h3 class="title"> 634<a name="boost_proto.appendices.acknowledgements"></a><a class="link" href="appendices.html#boost_proto.appendices.acknowledgements" title="Appendix E: Acknowledgements">Appendix E: 635 Acknowledgements</a> 636</h3></div></div></div> 637<p> 638 I'd like to thank Joel de Guzman and Hartmut Kaiser for being willing to 639 take a chance on using Proto for their work on Spirit-2 and Karma when Proto 640 was little more than a vision. Their requirements and feedback have been 641 indespensable. 642 </p> 643<p> 644 Thanks also to Thomas Heller and again to Hartmut for their feedback and 645 suggestions during the redesign of Phoenix. That effort yielded several valuable 646 advanced features such as sub-domains, external transforms, and per-domain 647 <code class="computeroutput"><span class="identifier">as_child</span></code> customization. 648 </p> 649<p> 650 Thanks to Daniel James for providing a patch to remove the dependence on 651 deprecated configuration macros for C++0x features. 652 </p> 653<p> 654 Thanks to Joel Falcou and Christophe Henry for their enthusiasm, support, 655 feedback, and humor; and for volunteering to be Proto's co-maintainers. 656 </p> 657<p> 658 Thanks to Dave Abrahams for an especially detailed review, and for making 659 a VM with msvc-7.1 available so I could track down portability issues on 660 that compiler. 661 </p> 662<p> 663 Many thanks to Daniel Wallin who first implemented the code used to find 664 the common domain among a set, accounting for super- and sub-domains. Thanks 665 also to Jeremiah Willcock, John Bytheway and Krishna Achuthan who offered 666 alternate solutions to this tricky programming problem. 667 </p> 668<p> 669 Thanks also to the developers of <a href="http://acts.nersc.gov/formertools/pete/index.html" target="_top">PETE</a>. 670 I found many good ideas there. 671 </p> 672</div> 673</div> 674<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr> 675<td align="left"></td> 676<td align="right"><div class="copyright-footer">Copyright © 2008 Eric Niebler<p> 677 Distributed under the Boost Software License, Version 1.0. (See accompanying 678 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>) 679 </p> 680</div></td> 681</tr></table> 682<hr> 683<div class="spirit-nav"> 684<a accesskey="p" href="../Transform.html"><img src="../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../proto.html"><img src="../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../boost_random.html"><img src="../../../doc/src/images/next.png" alt="Next"></a> 685</div> 686</body> 687</html> 688
