<li><a href="#hl_dontinclude">#include as Little as Possible</a></li>
<li><a href="#hl_privateheaders">Keep "internal" Headers
Private</a></li>
- <li><a href="#ll_iostream"><tt>#include <iostream></tt> is
- <em>forbidden</em></a></li>
+ <li><a href="#hl_earlyexit">Use Early Exits and 'continue' to Simplify
+ Code</a></li>
+ <li><a href="#hl_else_after_return">Don't use "else" after a
+ return</a></li>
+ <li><a href="#hl_predicateloops">Turn Predicate Loops into Predicate
+ Functions</a></li>
</ol></li>
<li><a href="#micro">The Low Level Issues</a>
<ol>
classes in headers</a></li>
<li><a href="#ll_end">Don't evaluate end() every time through a
loop</a></li>
- <li><a href="#ll_preincrement">Prefer Preincrement</a></li>
+ <li><a href="#ll_iostream"><tt>#include <iostream></tt> is
+ <em>forbidden</em></a></li>
<li><a href="#ll_avoidendl">Avoid <tt>std::endl</tt></a></li>
+ <li><a href="#ll_raw_ostream">Use <tt>raw_ostream</tt></a</li>
</ol></li>
+
+ <li><a href="#nano">Microscopic Details</a>
+ <ol>
+ <li><a href="#micro_spaceparen">Spaces Before Parentheses</a></li>
+ <li><a href="#micro_preincrement">Prefer Preincrement</a></li>
+ <li><a href="#micro_namespaceindent">Namespace Indentation</a></li>
+ <li><a href="#micro_anonns">Anonymous Namespaces</a></li>
+ </ol></li>
+
+
</ol></li>
<li><a href="#seealso">See Also</a></li>
</ol>
<div class="doc_author">
- <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
- <a href="mailto:void@nondot.org">Bill Wendling</a></p>
+ <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
</div>
<div class="doc_text">
<p>Comments are one critical part of readability and maintainability. Everyone
-knows they should comment, so should you. Although we all should probably
+knows they should comment, so should you. When writing comments, write them as
+English prose, which means they should use proper capitalization, punctuation,
+etc. Although we all should probably
comment our code more than we do, there are a few very critical places that
documentation is very useful:</p>
<b>Method information</b>
<p>Methods defined in a class (as well as any global functions) should also be
-documented properly. A quick note about what it does any a description of the
+documented properly. A quick note about what it does and a description of the
borderline behaviour is all that is necessary here (unless something
-particularly tricky or insideous is going on). The hope is that people can
+particularly tricky or insidious is going on). The hope is that people can
figure out how to use your interfaces without reading the code itself... that is
the goal metric.</p>
<div class="doc_text">
<p>In all cases, prefer spaces to tabs in source files. People have different
-prefered indentation levels, and different styles of indentation that they
+preferred indentation levels, and different styles of indentation that they
like... this is fine. What isn't is that different editors/viewers expand tabs
out to different tab stops. This can cause your code to look completely
unreadable, and it is not worth dealing with.</p>
declare the symbol. This can lead to problems at link time.</p>
<p>So, the rule for LLVM is to always use the <tt>class</tt> keyword, unless
-<b>all</b> members are public, in which case <tt>struct</tt> is allowed.</p>
+<b>all</b> members are public and the type is a C++ "POD" type, in which case
+<tt>struct</tt> is allowed.</p>
</div>
<div class="doc_subsection">
<a name="macro">The High Level Issues</a>
</div>
+<!-- ======================================================================= -->
<!-- _______________________________________________________________________ -->
<b>must</b> include all of the header files that you are using -- you can
include them either directly
or indirectly (through another header file). To make sure that you don't
-accidently forget to include a header file in your module header, make sure to
+accidentally forget to include a header file in your module header, make sure to
include your module header <b>first</b> in the implementation file (as mentioned
above). This way there won't be any hidden dependencies that you'll find out
about later...</p>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
- <a name="ll_iostream"><tt>#include <iostream></tt> is forbidden</a>
+ <a name="hl_earlyexit">Use Early Exits and 'continue' to Simplify Code</a>
</div>
<div class="doc_text">
-<p>The use of <tt>#include <iostream></tt> in library files is
-hereby <b><em>forbidden</em></b>. The primary reason for doing this is to
-support clients using LLVM libraries as part of larger systems. In particular,
-we statically link LLVM into some dynamic libraries. Even if LLVM isn't used,
-the static c'tors are run whenever an application start up that uses the dynamic
-library. There are two problems with this:</p>
+<p>When reading code, keep in mind how much state and how many previous
+decisions have to be remembered by the reader to understand a block of code.
+Aim to reduce indentation where possible when it doesn't make it more difficult
+to understand the code. One great way to do this is by making use of early
+exits and the 'continue' keyword in long loops. As an example of using an early
+exit from a function, consider this "bad" code:</p>
-<ol>
- <li>The time to run the static c'tors impacts startup time of
- applications—a critical time for GUI apps.</li>
- <li>The static c'tors cause the app to pull many extra pages of memory off the
- disk: both the code for the static c'tors in each <tt>.o</tt> file and the
- small amount of data that gets touched. In addition, touched/dirty pages
- put more pressure on the VM system on low-memory machines.</li>
-</ol>
+<div class="doc_code">
+<pre>
+Value *DoSomething(Instruction *I) {
+ if (!isa<TerminatorInst>(I) &&
+ I->hasOneUse() && SomeOtherThing(I)) {
+ ... some long code ....
+ }
+
+ return 0;
+}
+</pre>
+</div>
-<p>Note that using the other stream headers (<tt><sstream></tt> for
-example) is allowed normally, it is just <tt><iostream></tt> that is
-causing problems.</p>
+<p>This code has several problems if the body of the 'if' is large. When you're
+looking at the top of the function, it isn't immediately clear that this
+<em>only</em> does interesting things with non-terminator instructions, and only
+applies to things with the other predicates. Second, it is relatively difficult
+to describe (in comments) why these predicates are important because the if
+statement makes it difficult to lay out the comments. Third, when you're deep
+within the body of the code, it is indented an extra level. Finally, when
+reading the top of the function, it isn't clear what the result is if the
+predicate isn't true, you have to read to the end of the function to know that
+it returns null.</p>
+
+<p>It is much preferred to format the code like this:</p>
+
+<div class="doc_code">
+<pre>
+Value *DoSomething(Instruction *I) {
+ // Terminators never need 'something' done to them because, ...
+ if (isa<TerminatorInst>(I))
+ return 0;
+
+ // We conservatively avoid transforming instructions with multiple uses
+ // because goats like cheese.
+ if (!I->hasOneUse())
+ return 0;
+
+ // This is really just here for example.
+ if (!SomeOtherThing(I))
+ return 0;
+
+ ... some long code ....
+}
+</pre>
+</div>
+
+<p>This fixes these problems. A similar problem frequently happens in for
+loops. A silly example is something like this:</p>
+
+<div class="doc_code">
+<pre>
+ for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
+ if (BinaryOperator *BO = dyn_cast<BinaryOperator>(II)) {
+ Value *LHS = BO->getOperand(0);
+ Value *RHS = BO->getOperand(1);
+ if (LHS != RHS) {
+ ...
+ }
+ }
+ }
+</pre>
+</div>
-<p>The preferred replacement for stream functionality is the
-<tt>llvm::raw_ostream</tt> class (for writing to output streams of various
-sorts) and the <tt>llvm::MemoryBuffer</tt> API (for reading in files).</p>
+<p>When you have very very small loops, this sort of structure is fine, but if
+it exceeds more than 10-15 lines, it becomes difficult for people to read and
+understand at a glance.
+The problem with this sort of code is that it gets very nested very quickly,
+meaning that the reader of the code has to keep a lot of context in their brain
+to remember what is going immediately on in the loop, because they don't know
+if/when the if conditions will have elses etc. It is strongly preferred to
+structure the loop like this:</p>
+
+<div class="doc_code">
+<pre>
+ for (BasicBlock::iterator II = BB->begin(), E = BB->end(); II != E; ++II) {
+ BinaryOperator *BO = dyn_cast<BinaryOperator>(II);
+ if (!BO) continue;
+
+ Value *LHS = BO->getOperand(0);
+ Value *RHS = BO->getOperand(1);
+ if (LHS == RHS) continue;
+ }
+</pre>
+</div>
+
+<p>This has all the benefits of using early exits from functions: it reduces
+nesting of the loop, it makes it easier to describe why the conditions are true,
+and it makes it obvious to the reader that there is no "else" coming up that
+they have to push context into their brain for. If a loop is large, this can
+be a big understandability win.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="hl_else_after_return">Don't use "else" after a return</a>
+</div>
+
+<div class="doc_text">
+
+<p>For similar reasons above (reduction of indentation and easier reading),
+ please do not use "else" or "else if" after something that interrupts
+ control flow like return, break, continue, goto, etc. For example, this is
+ "bad":</p>
+
+<div class="doc_code">
+<pre>
+ case 'J': {
+ if (Signed) {
+ Type = Context.getsigjmp_bufType();
+ if (Type.isNull()) {
+ Error = ASTContext::GE_Missing_sigjmp_buf;
+ return QualType();
+ } else {
+ break;
+ }
+ } else {
+ Type = Context.getjmp_bufType();
+ if (Type.isNull()) {
+ Error = ASTContext::GE_Missing_jmp_buf;
+ return QualType();
+ } else {
+ break;
+ }
+ }
+ }
+ }
+</pre>
+</div>
+
+<p>It is better to write this something like:</p>
+
+<div class="doc_code">
+<pre>
+ case 'J':
+ if (Signed) {
+ Type = Context.getsigjmp_bufType();
+ if (Type.isNull()) {
+ Error = ASTContext::GE_Missing_sigjmp_buf;
+ return QualType();
+ }
+ } else {
+ Type = Context.getjmp_bufType();
+ if (Type.isNull()) {
+ Error = ASTContext::GE_Missing_jmp_buf;
+ return QualType();
+ }
+ }
+ break;
+</pre>
+</div>
+
+<p>Or better yet (in this case), as:</p>
+
+<div class="doc_code">
+<pre>
+ case 'J':
+ if (Signed)
+ Type = Context.getsigjmp_bufType();
+ else
+ Type = Context.getjmp_bufType();
+
+ if (Type.isNull()) {
+ Error = Signed ? ASTContext::GE_Missing_sigjmp_buf :
+ ASTContext::GE_Missing_jmp_buf;
+ return QualType();
+ }
+ break;
+</pre>
+</div>
+
+<p>The idea is to reduce indentation and the amount of code you have to keep
+ track of when reading the code.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="hl_predicateloops">Turn Predicate Loops into Predicate Functions</a>
+</div>
+
+<div class="doc_text">
+
+<p>It is very common to write small loops that just compute a boolean
+ value. There are a number of ways that people commonly write these, but an
+ example of this sort of thing is:</p>
+
+<div class="doc_code">
+<pre>
+ <b>bool FoundFoo = false;</b>
+ for (unsigned i = 0, e = BarList.size(); i != e; ++i)
+ if (BarList[i]->isFoo()) {
+ <b>FoundFoo = true;</b>
+ break;
+ }
+
+ <b>if (FoundFoo) {</b>
+ ...
+ }
+</pre>
+</div>
+
+<p>This sort of code is awkward to write, and is almost always a bad sign.
+Instead of this sort of loop, we strongly prefer to use a predicate function
+(which may be <a href="#micro_anonns">static</a>) that uses
+<a href="#hl_earlyexit">early exits</a> to compute the predicate. We prefer
+the code to be structured like this:
+</p>
+
+
+<div class="doc_code">
+<pre>
+/// ListContainsFoo - Return true if the specified list has an element that is
+/// a foo.
+static bool ListContainsFoo(const std::vector<Bar*> &List) {
+ for (unsigned i = 0, e = List.size(); i != e; ++i)
+ if (List[i]->isFoo())
+ return true;
+ return false;
+}
+...
+
+ <b>if (ListContainsFoo(BarList)) {</b>
+ ...
+ }
+</pre>
+</div>
+
+<p>There are many reasons for doing this: it reduces indentation and factors out
+code which can often be shared by other code that checks for the same predicate.
+More importantly, it <em>forces you to pick a name</em> for the function, and
+forces you to write a comment for it. In this silly example, this doesn't add
+much value. However, if the condition is complex, this can make it a lot easier
+for the reader to understand the code that queries for this predicate. Instead
+of being faced with the in-line details of how we check to see if the BarList
+contains a foo, we can trust the function name and continue reading with better
+locality.</p>
</div>
<div class="doc_subsection">
<a name="micro">The Low Level Issues</a>
</div>
+<!-- ======================================================================= -->
<!-- _______________________________________________________________________ -->
<div class="doc_text">
<p>Use the "<tt>assert</tt>" function to its fullest. Check all of your
-preconditions and assumptions, you never know when a bug (not neccesarily even
+preconditions and assumptions, you never know when a bug (not necessarily even
yours) might be caught early by an assertion, which reduces debugging time
dramatically. The "<tt><cassert></tt>" header file is probably already
included by the header files you are using, so it doesn't cost anything to use
semantics: if the container (a basic block in this case) is being mutated, then
"<tt>BB->end()</tt>" may change its value every time through the loop and the
second loop may not in fact be correct. If you actually do depend on this
-behavior, please write the loop in the second form and add a comment indicating
+behavior, please write the loop in the first form and add a comment indicating
that you did it intentionally.</p>
<p>Why do we prefer the second form (when correct)? Writing the loop in the
loads every time through the loop. However, if the base expression is more
complex, then the cost can rise quickly. I've seen loops where the end
expression was actually something like: "<tt>SomeMap[x]->end()</tt>" and map
-lookups really aren't cheap. By writing it in the first form consistently, you
+lookups really aren't cheap. By writing it in the second form consistently, you
eliminate the issue entirely and don't even have to think about it.</p>
-<p>The second (even bigger) issue is that writing the loop in the second form
+<p>The second (even bigger) issue is that writing the loop in the first form
hints to the reader that the loop is mutating the container (a fact that a
comment would handily confirm!). If you write the loop in the second form, it
is immediately obvious without even looking at the body of the loop that the
</div>
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="ll_iostream"><tt>#include <iostream></tt> is forbidden</a>
+</div>
+
+<div class="doc_text">
+
+<p>The use of <tt>#include <iostream></tt> in library files is
+hereby <b><em>forbidden</em></b>. The primary reason for doing this is to
+support clients using LLVM libraries as part of larger systems. In particular,
+we statically link LLVM into some dynamic libraries. Even if LLVM isn't used,
+the static c'tors are run whenever an application start up that uses the dynamic
+library. There are two problems with this:</p>
+
+<ol>
+ <li>The time to run the static c'tors impacts startup time of
+ applications—a critical time for GUI apps.</li>
+ <li>The static c'tors cause the app to pull many extra pages of memory off the
+ disk: both the code for the static c'tors in each <tt>.o</tt> file and the
+ small amount of data that gets touched. In addition, touched/dirty pages
+ put more pressure on the VM system on low-memory machines.</li>
+</ol>
+
+<p>Note that using the other stream headers (<tt><sstream></tt> for
+example) is not problematic in this regard (just <tt><iostream></tt>).
+However, raw_ostream provides various APIs that are better performing for almost
+every use than std::ostream style APIs, so you should just use it for new
+code.</p>
+
+<p><b>New code should always
+use <a href="#ll_raw_ostream"><tt>raw_ostream</tt></a> for writing, or
+the <tt>llvm::MemoryBuffer</tt> API for reading files.</b></p>
+
+</div>
+
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="ll_avoidendl">Avoid <tt>std::endl</tt></a>
+</div>
+
+<div class="doc_text">
+
+<p>The <tt>std::endl</tt> modifier, when used with iostreams outputs a newline
+to the output stream specified. In addition to doing this, however, it also
+flushes the output stream. In other words, these are equivalent:</p>
+
+<div class="doc_code">
+<pre>
+std::cout << std::endl;
+std::cout << '\n' << std::flush;
+</pre>
+</div>
+
+<p>Most of the time, you probably have no reason to flush the output stream, so
+it's better to use a literal <tt>'\n'</tt>.</p>
+
+</div>
+
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="ll_raw_ostream">Use <tt>raw_ostream</tt></a>
+</div>
+
+<div class="doc_text">
+
+<p>LLVM includes a lightweight, simple, and efficient stream implementation
+in <tt>llvm/Support/raw_ostream.h</tt> which provides all of the common features
+of <tt>std::ostream</tt>. All new code should use <tt>raw_ostream</tt> instead
+of <tt>ostream</tt>.</p>
+
+<p>Unlike <tt>std::ostream</tt>, <tt>raw_ostream</tt> is not a template and can
+be forward declared as <tt>class raw_ostream</tt>. Public headers should
+generally not include the <tt>raw_ostream</tt> header, but use forward
+declarations and constant references to <tt>raw_ostream</tt> instances.</p>
+
+</div>
+
+
+<!-- ======================================================================= -->
+<div class="doc_subsection">
+ <a name="nano">Microscopic Details</a>
+</div>
+<!-- ======================================================================= -->
+
+<p>This section describes preferred low-level formatting guidelines along with
+reasoning on why we prefer them.</p>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="micro_spaceparen">Spaces Before Parentheses</a>
+</div>
+
+<div class="doc_text">
+
+<p>We prefer to put a space before a parentheses only in control flow
+statements, but not in normal function call expressions and function-like
+macros. For example, this is good:</p>
+
+<div class="doc_code">
+<pre>
+ <b>if (</b>x) ...
+ <b>for (</b>i = 0; i != 100; ++i) ...
+ <b>while (</b>llvm_rocks) ...
+
+ <b>somefunc(</b>42);
+ <b><a href="#ll_assert">assert</a>(</b>3 != 4 && "laws of math are failing me");
+
+ a = <b>foo(</b>42, 92) + <b>bar(</b>x);
+ </pre>
+</div>
+
+<p>... and this is bad:</p>
+
+<div class="doc_code">
+<pre>
+ <b>if(</b>x) ...
+ <b>for(</b>i = 0; i != 100; ++i) ...
+ <b>while(</b>llvm_rocks) ...
+
+ <b>somefunc (</b>42);
+ <b><a href="#ll_assert">assert</a> (</b>3 != 4 && "laws of math are failing me");
+
+ a = <b>foo (</b>42, 92) + <b>bar (</b>x);
+</pre>
+</div>
+
+<p>The reason for doing this is not completely arbitrary. This style makes
+ control flow operators stand out more, and makes expressions flow better. The
+ function call operator binds very tightly as a postfix operator. Putting
+ a space after a function name (as in the last example) makes it appear that
+ the code might bind the arguments of the left-hand-side of a binary operator
+ with the argument list of a function and the name of the right side. More
+ specifically, it is easy to misread the "a" example as:</p>
+
+<div class="doc_code">
+<pre>
+ a = foo <b>(</b>(42, 92) + bar<b>)</b> (x);
+</pre>
+</div>
+
+<p>... when skimming through the code. By avoiding a space in a function, we
+avoid this misinterpretation.</p>
+
+</div>
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
- <a name="ll_preincrement">Prefer Preincrement</a>
+ <a name="micro_preincrement">Prefer Preincrement</a>
</div>
<div class="doc_text">
<!-- _______________________________________________________________________ -->
<div class="doc_subsubsection">
- <a name="ll_avoidendl">Avoid <tt>std::endl</tt></a>
+ <a name="micro_namespaceindent">Namespace Indentation</a>
</div>
<div class="doc_text">
-<p>The <tt>std::endl</tt> modifier, when used with iostreams outputs a newline
-to the output stream specified. In addition to doing this, however, it also
-flushes the output stream. In other words, these are equivalent:</p>
+<p>
+In general, we strive to reduce indentation where ever possible. This is useful
+because we want code to <a href="#scf_codewidth">fit into 80 columns</a> without
+wrapping horribly, but also because it makes it easier to understand the code.
+Namespaces are a funny thing: they are often large, and we often desire to put
+lots of stuff into them (so they can be large). Other times they are tiny,
+because they just hold an enum or something similar. In order to balance this,
+we use different approaches for small versus large namespaces.
+</p>
+
+<p>
+If a namespace definition is small and <em>easily</em> fits on a screen (say,
+less than 35 lines of code), then you should indent its body. Here's an
+example:
+</p>
<div class="doc_code">
<pre>
-std::cout << std::endl;
-std::cout << '\n' << std::flush;
+namespace llvm {
+ namespace X86 {
+ /// RelocationType - An enum for the x86 relocation codes. Note that
+ /// the terminology here doesn't follow x86 convention - word means
+ /// 32-bit and dword means 64-bit.
+ enum RelocationType {
+ /// reloc_pcrel_word - PC relative relocation, add the relocated value to
+ /// the value already in memory, after we adjust it for where the PC is.
+ reloc_pcrel_word = 0,
+
+ /// reloc_picrel_word - PIC base relative relocation, add the relocated
+ /// value to the value already in memory, after we adjust it for where the
+ /// PIC base is.
+ reloc_picrel_word = 1,
+
+ /// reloc_absolute_word, reloc_absolute_dword - Absolute relocation, just
+ /// add the relocated value to the value already in memory.
+ reloc_absolute_word = 2,
+ reloc_absolute_dword = 3
+ };
+ }
+}
</pre>
</div>
-<p>Most of the time, you probably have no reason to flush the output stream, so
-it's better to use a literal <tt>'\n'</tt>.</p>
+<p>Since the body is small, indenting adds value because it makes it very clear
+where the namespace starts and ends, and it is easy to take the whole thing in
+in one "gulp" when reading the code. If the blob of code in the namespace is
+larger (as it typically is in a header in the llvm or clang namespaces), do not
+indent the code, and add a comment indicating what namespace is being closed.
+For example:</p>
+<div class="doc_code">
+<pre>
+namespace llvm {
+namespace knowledge {
+
+/// Grokable - This class represents things that Smith can have an intimate
+/// understanding of and contains the data associated with it.
+class Grokable {
+...
+public:
+ explicit Grokable() { ... }
+ virtual ~Grokable() = 0;
+
+ ...
+
+};
+
+} // end namespace knowledge
+} // end namespace llvm
+</pre>
</div>
+<p>Because the class is large, we don't expect that the reader can easily
+understand the entire concept in a glance, and the end of the file (where the
+namespaces end) may be a long ways away from the place they open. As such,
+indenting the contents of the namespace doesn't add any value, and detracts from
+the readability of the class. In these cases it is best to <em>not</em> indent
+the contents of the namespace.</p>
+
+</div>
+
+<!-- _______________________________________________________________________ -->
+<div class="doc_subsubsection">
+ <a name="micro_anonns">Anonymous Namespaces</a>
+</div>
+
+<div class="doc_text">
+
+<p>After talking about namespaces in general, you may be wondering about
+anonymous namespaces in particular.
+Anonymous namespaces are a great language feature that tells the C++ compiler
+that the contents of the namespace are only visible within the current
+translation unit, allowing more aggressive optimization and eliminating the
+possibility of symbol name collisions. Anonymous namespaces are to C++ as
+"static" is to C functions and global variables. While "static" is available
+in C++, anonymous namespaces are more general: they can make entire classes
+private to a file.</p>
+
+<p>The problem with anonymous namespaces is that they naturally want to
+encourage indentation of their body, and they reduce locality of reference: if
+you see a random function definition in a C++ file, it is easy to see if it is
+marked static, but seeing if it is in an anonymous namespace requires scanning
+a big chunk of the file.</p>
+
+<p>Because of this, we have a simple guideline: make anonymous namespaces as
+small as possible, and only use them for class declarations. For example, this
+is good:</p>
+
+<div class="doc_code">
+<pre>
+<b>namespace {</b>
+ class StringSort {
+ ...
+ public:
+ StringSort(...)
+ bool operator<(const char *RHS) const;
+ };
+<b>} // end anonymous namespace</b>
+
+static void Helper() {
+ ...
+}
+
+bool StringSort::operator<(const char *RHS) const {
+ ...
+}
+
+</pre>
+</div>
+
+<p>This is bad:</p>
+
+
+<div class="doc_code">
+<pre>
+<b>namespace {</b>
+class StringSort {
+...
+public:
+ StringSort(...)
+ bool operator<(const char *RHS) const;
+};
+
+void Helper() {
+ ...
+}
+
+bool StringSort::operator<(const char *RHS) const {
+ ...
+}
+
+<b>} // end anonymous namespace</b>
+
+</pre>
+</div>
+
+
+<p>This is bad specifically because if you're looking at "Helper" in the middle
+of a large C++ file, that you have no immediate way to tell if it is local to
+the file. When it is marked static explicitly, this is immediately obvious.
+Also, there is no reason to enclose the definition of "operator<" in the
+namespace just because it was declared there.
+</p>
+
+</div>
+
+
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