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      <h3><a href="index.html"><img height="86" width="277" alt="C++ Boost" src="../../boost.png" border="0"></a></h3>
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      <h1 align="center">Writing Documentation for Boost</h1>
      <h2 align="center">Documentation Structure</h2>
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<dl class="page-index">
  <dt><a href="#introduction">Introduction</a></dt>
  <dt><a href="#standards-conforming">Standards Conforming Documentation</a></dt>
  <dl class="page-index">
    <dt><a href="#elements">Document elements</a></dt>
	<dl class="page-index">
	  <dt><a href="#summary">Summary</a></dt>
      <dt><a href="#requirements">Requirements</a></dt>
      <dt><a href="#detailed-specs">Detailed specifications</a></dt>
      <dt><a href="#ref-cpp">References to the Standard C++ library</a></dt>
      <dt><a href="#ref-c">References to the Standard C library</a></dt>
	</dl>
	<dt><a href="#other">Other conventions</a></dt>
	<dl class="page-index">
	  <dt><a href="#type-descs">Type descriptions</a></dt>
	</dl>
  </dl>
  <dt><a href="#more">More Information</a></dt>
  <dl class="page-index">
    <dt><a href="#function-semantic-explanations">Function semantic element explanations</a></dt>
	<dl class="page-index">
	  <dt><a href="#requires">Requires</a></dt>
	  <dt><a href="#effects">Effects</a></dt>
	  <dt><a href="#postconditions">Postconditions</a></dt>
	  <dt><a href="#returns">Returns</a></dt>
	  <dt><a href="#throws">Throws</a></dt>
	  <dt><a href="#complexity">Complexity</a></dt>
	  <dt><a href="#rationale">Rationale</a></dt>
	</dl>
  </dl>
  <dt><a href="#footnotes">Footnotes</a></dt>
</dl>
<h2><a name="introduction">Introduction</a></h2>
<p>Boost itself does not require any specific documentation structure. The C++ 
  Standard, however, has very explicit requirements for the description of library 
  components (Section 17.3). So for Boost libraries likely to be proposed for 
  inclusion in the standard, it is highly desirable to structure documentation 
  in a way that meets the requirements of the the standard. Doing so eliminates 
  the need to rewrite the documentation for standardization.</p>
<p>Library developers should remember that for a library to be accepted as part 
  of the C++ Standard Library, the proposal must include full wording. The committee 
  will not do that work for you.</p>
<p>Beyond that, the documentation structure required for the standard is an effective 
  way to communicate the technical specifications for a library. Although terse, 
  it is already familiar to many Boost users, and is far more precise than most 
  ad hoc documentation structures.</p>
<p>The following description is for the structure of documentation required by 
  the standard. Boost libraries should also provided additional documentation, 
  such as introductory, tutorial, example, and rationale material.</p>
<h2><a name="standards-conforming">Standards Conforming</a> Documentation</h2>
<h3><a name="elements">Document elements</a></h3>
<p>Each document contains the following elements, as applicable<a class="footnote" href="#footnote1">(1)</a>:</p>
<ul>
  <li><a href="#summary">Summary</a></li>
  <li><a href="#requirements">Requirements</a></li>
  <li><a href="#detailed-specs">Detailed specifications</a></li>
  <li><a href="#ref-cpp">References to the Standard C++ library</a></li>
  <li><a href="#ref-c">References to the Standard C library</a></li>
</ul>
<h4><a name="summary">Summary</a></h4>
<p>The Summary provides a synopsis of the category, and introduces the first-level 
  subclauses. Each subclause also provides a summary, listing the headers specified 
  in the subclause and the library entities provided in each header.</p>
<p>Paragraphs labeled "Note(s):" or "Example(s):" are informative, other paragraphs 
  are normative.</p>
<p>The summary and the detailed specifications are presented in the order:</p>
<ul>
  <li>Macros</li>
  <li>Values</li>
  <li>Types</li>
  <li>Classes</li>
  <li>Functions</li>
  <li>Objects</li>
</ul>
<h4><a name="requirements">Requirements</a></h4>
<p>The library can be extended by a C++ program. Each clause, as applicable, describes 
  the requirements that such extensions must meet. Such extensions are generally 
  one of the following:</p>
<ul>
  <li>Template arguments</li>
  <li>Derived classes</li>
  <li>Containers, iterators, and/or algorithms that meet an interface convention</li>
</ul>
<p>Interface convention requirements are stated as generally as possible. Instead 
  of stating "<code>class X</code> has to define a member function <code>operator++()</code>," 
  the interface requires "for any object <code>x</code> of <code>class X</code>, 
  <code>++x</code> is defined." That is, whether the operator is a member is unspecified.</p>
<p>Requirements are stated in terms of well-defined expressions, which define 
  valid terms of the types that satisfy the requirements. For every set of requirements 
  there is a table that specifies an initial set of the valid expressions and 
  their semantics. Any generic algorithm that uses the requirements is described 
  in terms of the valid expressions for its formal type parameters.</p>
<p>Template argument requirements are sometimes referenced by name.</p>
<p>In some cases the semantic requirements are presented as C++ code. Such code 
  is intended as a specification of equivalance of a construct to another construct, 
  not necessarily as the way the construct must be implemented.<a class="footnote" href="#footnote2">(2)</a></p>
<h4><a name="detailed-specs">Detailed specification</a></h4>
<p>The detailed specifications each contain the following elements:</p>
<ul>
  <li>Name and brief description</li>
  <li>Synopsis (class definition or function prototype, as appropriate)</li>
  <li>Restrictions on template arguments, if any</li>
  <li>Description of class invariants</li>
  <li>Description of function semantics</li>
</ul>
<p>Descriptions of class member functions follow the order (as appropriate)<a class="footnote" href="#footnote3">(3)</a>:</p>
<ul>
  <li>Constructor(s) and destructor</li>
  <li>Copying and assignment functions</li>
  <li>Comparison functions</li>
  <li>Modifier functions</li>
  <li>Observer functions</li>
  <li>Operators and other non-member functions</li>
</ul>
<p>Descriptions of function semantics contain the following <a name="function-elements">elements</a> 
  (as appropriate)<a class="footnote" href="#footnote4">(4):</a></p>
<dl class="function-semantics">
  <dt><b><a href="#requires">Requires:</a></b> the preconditions for calling the 
    function</dt>
  <dt><b><a href="#effects">Effects:</a></b> the actions performed by the function</dt>
  <dt><b><a href="#postconditions">Postconditions:</a></b> the observable results 
    established by the function</dt>
  <dt><b><a href="#returns">Returns:</a></b> a description of the value(s) returned 
    by the function</dt>
  <dt><b><a href="#throws">Throws:</a></b> any exceptions thrown by the function, 
    and the conditions that would cause the exception</dt>
  <dt><b><a href="#complexity">Complexity:</a></b> the time and/or space complexity 
    of the function</dt>
  <dt><b><a href="#rationale">Rationale:</a></b> the rationale for the function's design
    or existence</dt>
</dl>
<p>Complexity requirements specified in the library clauses are upper bounds, 
  and implementations that provide better complexity guarantees satisfy the requirements.</p>
<h4><a name="ref-cpp">References to the C++ Standard library</a></h4>
<h4><a name="ref-c">References to the C Standard library</a></h4>
<h3><a name="other">Other conventions</a></h3>
<p>These conventions are for describing implementation-defined types, and member 
  functions.</p>
<h4><a name="type-descs">Type descriptions</a></h4>
<p>The Requirements subclauses may describe names that are used to specify constraints 
  on template arguments.</p>
<h2><a name="more">More Information</a></h2>
<h3><a name="function-semantic-explanations">Function semantic element explanations</a></h3>
<p>The function semantic element description <a href="#function-elements">above</a> 
  is taken directly from the C++ standard, and is quite terse. Here is a more 
  detailed explanation of each of the elements.</p>
<p>Note the use of the <code>&lt;code&gt; ... &lt;/code&gt;</code> font tag to 
  distinguish actual C++ usage from English prose.</p>
<h4><a name="requires">Requires</a></h4>
<p>Preconditions for calling the function, typically expressed as predicates. 
  The most common preconditions are requirements on the value of arguments, often 
  in the form of C++ expressions. For example, 
<pre> 
<code>void limit( int * p, int min, int max );</code>
</pre>
<dl class="function-semantics">
  <dt><b>Requires:</b> <code>p != 0 &amp;&amp; min &lt;= max</code></dt>
</dl>
<p>Requirements already enforced by the C++ language rules (such as the type of 
  arguments) are not repeated in Requires paragraphs.</p>
<h4><a name="effects">Effects</a></h4>
<p>The actions performed by the function, described either in prose or in C++. 
  A description in prose is often less limiting on implementors, but is often 
  less precise than C++ code.</p>
<p>If an effect is specified in one of the other elements, particularly <i>postconditions</i>, 
  <i>returns</i>, or <i>throws</i>, it is not also described in the <i>effects</i> 
  paragraph. Having only a single description ensures that there is one and only 
  one specification, and thus eliminates the risk of divergence.</p>
<h4><a name="postconditions">Postconditions</a></h4>
<p>The observable results of the function, such as the value of variables. Postconditions 
  are often expressed as predicates that are true after the function completes, 
  in the form of C++ expressions. For example:</p>
<pre> 
void make_zero_if_negative( int &amp; x );
</pre>
<dl class="function-semantics">
  <dt><b>Postcondition:</b> <code>x &gt;= 0</code></dt>
</dl>
<h4><a name="returns">Returns</a></h4>
<p>The value returned by the function, usually in the form of a C++ expression. 
  For example:</p>
<pre>int sum( int x, int y );
</pre>
<dl class="function-semantics"> 
  <dt><b>Returns:</b> <code>x + y</code></dt>
</dl>
<p>Only specify the return value; the type is already dictated by C++ language 
  rules. 
<h4><a name="throws">Throws</a></h4>
<p>Specify both the type of exception thrown, and the condition that causes the 
  exception to be thrown. For example, the <code>std::basic_string</code> class 
  specifies: 
<pre> 
void resize(size_type n, charT c);
</pre>
<dl class="function-semantics">
  <dt><b>Throws:</b> <code> length_error</code> if <code>n &gt; max_size()</code>.</dt>
</dl>
<h4><a name="complexity">Complexity</a></h4>
<p>Specifying the time and/or space complexity of a function is often not desirable 
  because it over-constrains implementors and is hard to specify correctly. Complexity 
  is thus often best left as a quality of implementation issue.</p>
<p>A library component, however, can become effectively non-portable if there 
  is wide variation in performance between conforming implementations. Containers 
  are a prime example. In these cases it becomes worthwhile to specify complexity.</p>
<p>Complexity is often specified in generalized <a href="http://hissa.nist.gov/dads/HTML/bigOnotation.html"> 
  &quot;Big-O&quot; notation</a>.</p>
<h4><a name="rationale">Rationale</a></h4>
<p>Specifying the rationale for a function's design or existence can often give users
  a lot of insight into why a library is designed the way it is. More importantly, it
  can help prevent "fixing" something that wasn't really broken as the library matures.</p>  
<h2><a name="footnotes">Footnotes</a></h2>
<dl>
  <dt><a class="footnote" name="footnote1">(1)</a> 
    To save space, items that do not apply to a clause are omitted. For example, 
    if a clause does not specify any requirements, there will be no "Requirements" 
    subclause.</dt>
  <dt><a class="footnote" name="footnote2">(2)</a> Although in some cases the 
    code is unambiguously the optimum implementation.</dt>
  <dt><a class="footnote" name="footnote3">(3)</a> To save space, items that do 
    not apply to a class are omitted. For example, if a class does not specify 
    any comparison functions, there will be no "Comparison functions" subclause.</dt>
  <dt><a class="footnote" name="footnote4">(4)</a> To save space, items that do 
    not apply to a function are omitted. For example, if a function does not specify 
    any precondition, there will be no "Requires" paragraph.</dt>
</dl>
<hr>
<p>Revised 
  <!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->29 November, 2003<!--webbot bot="Timestamp" endspan i-checksum="39371" -->
</p>
<p><i>&copy; Copyright <a href="mailto:williamkempf@hotmail.com">William E. Kempf</a> 
  2001. All Rights Reserved.</i></p>
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