Add design patterns section

doc/index.html

@@ -186,14 +186,18 @@ integers. The types may be aligned.</p>
 <h2><a name="Choosing">Choosing</a> between  conversion functions,  buffer types, 
 and  arithmetic types</h2>
 
-<p>The best approach to endianness for a particular use case  depends on  interactions between 
+<p>The best approach to endianness for a particular application  depends on  the interaction between 
-the approach characteristics and  
+the application&#39;s needs and the characteristics of each of the three (conversion 
-the application needs.</p>
+functions, buffer types, or arithmetic types) approaches.</p>
 
-<p><b>Recommendation:</b> If you are uncertain, new to endianness, concerned 
+<p><b>Recommendation:</b> If you are new to endianness, uncertain, or don&#39;t want to invest 
-about security, concerned about reliability, or don&#39;t want to invest time making 
+the time to 
-engineering trade-offs, use the <a href="arithmetic.html">endian arithmetic types</a>. They are safer, easier 
+study 
-to use, and your code will be easier to maintain.</p>
+engineering trade-offs, use <a href="arithmetic.html">endian arithmetic types</a>. They are safe, easy 
+to use, and easy to maintain. Use the
+<a href="#Anticipating-need"> <i>
+anticipating need</i></a> design pattern locally around performance hot spots like lengthy loops, 
+if needed.&nbsp; </p>
 
 <h3><a name="Characteristics">Characteristics</a></h3>
 
@@ -292,6 +296,46 @@ needed they are often very useful and workarounds are painful. For example,</p>
 
 </blockquote>
 
+<h3><a name="Design-patterns">Design patterns</a></h3>
+
+<p>Applications often traffic in endian data as records or packets containing 
+multiple endian data elements. For simplicity, we will just call them records.</p>
+
+<p>If desired endianness differs from native endianness, a conversion has to be 
+performed. When should that conversion occur? Three design patterns have 
+evolved.</p>
+
+<h4><a name="As-needed">Convert only as needed</a> (i.e. lazy)</h4>
+
+<p>This pattern defers conversion to the point in the code where the data 
+element is actually used.</p>
+
+<p>This pattern is appropriate when which endian element is actually used varies 
+greatly according to record content or other circumstances</p>
+
+<h4><a name="Anticipating-need">Convert in anticipation of need</a></h4>
+
+<p>This pattern performs conversion to native endianness in anticipation of use, 
+such as immediately after reading records. If needed, conversion to the output 
+endianness is performed after all possible needs have passed, such as just 
+before writing records.</p>
+
+<p>One implementation of this pattern is to create a proxy record with 
+endianness converted to native in a read function, and expose only that proxy to 
+the rest of the implementation. If a write function, if needed, handles the 
+conversion from native to the desired output endianness.</p>
+
+<p>This pattern is appropriate when all endian elements in a record are 
+typically used regardless of record content or other circumstances</p>
+
+<h4>Convert generally only as needed, but locally in anticipation of need</h4>
+
+<p>This pattern in general defers conversion but does 
+anticipatory conversion for specific local needs.</p>
+
+<p>This pattern is particularly appropriate when coupled with the endian buffer 
+or arithmetic types.</p>
+
 <h3><a name="Use-cases">Use cases</a></h3>
 
 <h4><a name="Porting-endian-unaware-codebase">Porting endian unaware codebase</a></h4>
@@ -825,7 +869,7 @@ Blechmann, Tim Moore, tymofey, Tomas Puverle, Vincente Botet, Yuval Ronen and
 Vitaly Budovski,.</p>
 <hr>
 <p>Last revised:
-<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->17 December, 2014<!--webbot bot="Timestamp" endspan i-checksum="38647" --></p>
+<!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B, %Y" startspan -->31 December, 2014<!--webbot bot="Timestamp" endspan i-checksum="38637" --></p>
 <p>© Copyright Beman Dawes, 2011, 2013</p>
 <p>Distributed under the Boost Software License, Version 1.0. See
 <a href="http://www.boost.org/LICENSE_1_0.txt">www.boost.org/ LICENSE_1_0.txt</a></p>