Add a blurb about the use of class vs. struct keyword in class decls.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@16500 91177308-0d34-0410-b5e6-96231b3b80d8

docs/CodingStandards.html

@@ -29,6 +29,7 @@
           <li><a href="#ci_warningerrors">Treat Compiler Warnings Like
               Errors</a></li>
           <li><a href="#ci_portable_code">Write Portable Code</a></li>
+          <li><a href="#ci_class_struct">Use of class/struct Keywords</a></li>
         </ol></li>
     </ol></li>
   <li><a href="#styleissues">Style Issues</a>
@@ -366,6 +367,23 @@ to support it.</p>
 
 </div>
 
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+<a name="ci_class_struct">Use of <tt>class</tt> and <tt>struct</tt> Keywords</a>
+</div>
+<div class="doc_text">
+  <p>In C++ the <tt>class</tt> and <tt>struct</tt> keywoards can be used almost
+  interchangeably. The only difference is when they are used to declare a class:
+  <tt>class</tt> makes all members private by default while <tt>struct</tt>
+  makes all members public by defaut.<p>
+  <p>Unfortunately, not all compilers follow the rules and some will generate
+  different symbols based on whether <tt>class</tt> or <tt>struct</tt> was used
+  to declare the symbol. This can lead to problems at link time.</p>
+  <p>So, the rule for LLVM is this: "always use the <tt>class</tt> keyword, 
+  unless <b>all</b> members are public in which case <tt>struct</tt> is
+  allowed.</p>
+</div>
+
 <!-- *********************************************************************** -->
 <div class="doc_section">
   <a name="styleissues">Style Issues</a>