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Add a section about using namespaces.

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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@25054 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2006-01-01 21:59:22 +00:00
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@ -45,9 +45,9 @@
<li><a href="#micro">The Low Level Issues</a>
<ol>
<li><a href="#hl_assert">Assert Liberally</a></li>
<li><a href="#hl_ns_std">Do not use 'using namespace std'</a></li>
<li><a href="#hl_preincrement">Prefer Preincrement</a></li>
<li><a href="#hl_avoidendl">Avoid <tt>std::endl</tt></a></li>
<li><a href="#hl_exploitcpp">Exploit C++ to its Fullest</a></li>
</ol></li>
</ol></li>
<li><a href="#seealso">See Also</a></li>
@ -535,6 +535,40 @@ assert(isa&lt;PHINode&gt;(Succ-&gt;front()) &amp;&amp; "Only works on PHId BBs!"
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="hl_ns_std">Do not use 'using namespace std'</a>
</div>
<div class="doc_text">
<p>In LLVM, we prefer to explicitly prefix all identifiers from the standard
namespace with an "std::" prefix, rather than rely on "using namespace std;".
</p>
<p> In header files, adding a 'using namespace XXX' directive pollutes the
namespace of any source file that includes the header. This is clearly a bad
thing.</p>
<p>In implementation files (e.g. .cpp files) the rule is more of a stylistic
rule, but is still important. Basically, using explicit namespace prefixes
makes
the code <b>more clear</b> - because it is immediately obvious what facilities
are being used and where they are coming from - and <b>more portable</b> -
because namespace clashes cannot occur between LLVM code and other namespaces.
The portability rule is important because different standard library
implementations expose different symbols (potentially ones they shouldn't) and
future revisions to the C++ standard will add more symbols to the std
namespace. As such, we never 'using namespace std;' in LLVM.</p>
<p>The exception to the general rule (i.e. it's not an exception for the std
namespace) is for implementation files. For example, all of the code in the
LLVM project implements code that lives in the 'llvm' namespace. As such, it
is ok, and actually more clear, for the .cpp files to have a 'using namespace
llvm' directive at their top, after the #includes. The general form of this
rule is that any .cpp file that implements code in any namespace may use that
namespace (and its parents), but should not use any others.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
@ -579,25 +613,6 @@ it's better to use a literal <tt>'\n'</tt>.</p>
</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
<a name="hl_exploitcpp">Exploit C++ to its Fullest</a>
</div>
<div class="doc_text">
<p>C++ is a powerful language. With a firm grasp on its capabilities, you can
make write effective, consise, readable and maintainable code all at the same
time. By staying consistent, you reduce the amount of special cases that need
to be remembered. Reducing the total number of lines of code you write is a
good way to avoid documentation, and avoid giving bugs a place to hide.</p>
<p>For these reasons, come to know and love the contents of your local
<tt>&lt;algorithm&gt;</tt> header file. Know about <tt>&lt;functional&gt;</tt>
and what it can do for you. C++ is just a tool that wants you to master it.</p>
</div>
<!-- *********************************************************************** -->
<div class="doc_section">
<a name="seealso">See Also</a>