[Lldb-commits] [lldb] r223543 - First pass at a description of the lldb coding conventions.
jingham at apple.com
Fri Dec 5 15:18:01 PST 2014
Date: Fri Dec 5 17:18:01 2014
New Revision: 223543
First pass at a description of the lldb coding conventions.
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+<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1" />
+<link href="style.css" rel="stylesheet" type="text/css" />
+ <div class="www_title">
+ The <strong>LLDB</strong> Coding Conventions
+ <div id="content">
+ <!--#include virtual="sidebar.incl"-->
+ <div id="middle">
+ <div class="post">
+ <h1 class ="postheader">Getting Started</h1>
+ <div class="postcontent">
+ <p>The lldb coding conventions for the most part follow those used in llvm. For instance the
+ importance of comments, particularly for defining classes and methods, the restrictions on
+ features of C++ to use, and the generally excellent advice about using C++ features
+ properly should all be followed when writing code for lldb. However, lldb does differ
+ from the llvm coding conventions in several ways. This document outlines the most important ones.
+ <h3>Source code width:</h3>
+ <p>lldb does not follow the 80 character line restriction llvm imposes. In our
+ experience, trying to fit C++ code into an 80 character line results in code that
+ is awkward to read, and the time spent trying to find good indentation points to
+ avoid this would be much better spent on thinking about your code.
+ <p>More importantly, the restriction induces coders to choose overly abbreviated names
+ to make them better fit in 80 characters. In our opinion choosing good descriptive
+ names is much more important than fitting in 80 characters.
+ <p>In lldb, we don't have a hard character limit, though we try to keep code statements under
+ 120 characters because it gets awkward to scan longer lines even on a fairly big monitor,
+ and we've found at that length you seldom have to make code look ugly to get it to wrap.
+ <p>However you will see some instances of longer lines. The most common occurrence is in
+ the options tables for the CommandInterpreter, which contain the help strings as well as
+ a bunch of important but hard to remember fields. These tables are much easier to read if
+ all the fields line up vertically, and don't have help text interleaved in between the lines.
+ <p>lldb uses 4 character indentation. We find this makes the code structure much easier to
+ see when scanning code, and since we aren't trying to fit code into 80 characters, the
+ benefit of not wasting 2 out of the 80 precious spaces per indentation level is moot.
+ <p>We also use the Allman brace style rather than putting the initial brace at the end
+ of the braced line. This makes the block structure of the code much easier to see on
+ an initial scan, and most folks have big enough monitors nowadays that saving a few
+ vertical lines isn't sufficiently important to outweigh this benefit.
+ <p>Though the llvm coding conventions don't specify this, llvm/clang tend to declare and
+ define methods by putting the return type and the method name on the same line. lldb
+ puts the qualifiers and return type on a line by themselves and then the method name on
+ the next line, i.e.:
+ virtual int
+ MethodName ();
+ <p>When you are scanning a header file, that makes the method names stand out more easily,
+ though at the cost of an extra line. When you have a editor that scrolls smoothly, it's
+ easy to move through pages so the extra line is less important than the ease of picking
+ out the method names, which is what you generally are scanning for.
+ <p>Another place where lldb and llvm differ is in whether to put a space between a function
+ name, and the parenthesis that begins its argument list. In lldb, we insert a space between
+ the name and the parenthesis, except for functions that take no parameters, or when the
+ function is in a chain of functions calls. However, this rule has been applied rather
+ haphazardly in lldb at present.
+ <h3> Names:</h3>
+ <p>lldb's naming conventions are different and slightly more restrictive than the llvm
+ ones. The goal is to make it easy to tell from immediate context the lifespan
+ and what kind of entity a given name represents, which makes reading code you are not familiar
+ with much easier. lldb uses the following conventions:
+ <li> Macro definitions when needed are in all caps, nothing else should be in all caps. </li>
+ <li>Types and classes are in CamelCase with an initial capital.</li>
+ <li>Methods are also in CamelCase with an initial capital. The initial capital for methods
+ has the handy benefit that it gets our method names into a different namespace
+ than the standard C/C++ library functions, which tend to all be lower-cased.
+ There are also places in lldb where we wrap clang objects in classes appropriate to lldb,
+ and the difference from the llvm convention here actually makes it easier to tell
+ whether you are using the clang object directly or are going through the lldb wrapper.</li>
+ <li> All variables are written in lower case, with "_" as the word separator. We find that
+ using a different capitalization and word separation convention makes variables and methods/types
+ immediately visually distinct, resulting in code which is much easier to read.</li>
+ <li> class ivars all start with "m_". It is important to be able to tell ivars from local
+ variables, and this makes the distinction easily apparent. Some other coding conventions
+ use an initial "_", but this seems much harder to spot. Also it allows:</li>
+ <li> Class statics and other global variables start with "g_". You should be suspicious of all
+ global variables, so having them stand out lexically is a good thing.</li>
+ <li>We also use the suffixes "_sp" and "_up" for shared and unique pointer variables. Since
+ these have very different lifecycle behaviors it is worthwhile to call them out
+ specially. You will see some "_ap" suffixes around. There should be no auto_ptr variables
+ left in lldb, but when we converted to unique_ptr's not all the names were changed.
+ Feel free to change these to "_up" when you touch them for some other reason.</li>
+ <li> enumerations that might end up being in the lldb SB API's should all be written like:
+ typedef enum EnumName
+ } EnumName;
+ <p>This redundancy is important because the enumerations that find their way through SWIG into
+ Python will show up as lldb.eEnumNameFirstValue, so including the enum name
+ in the value name disambiguates them in Python.
+ <p>Since we've started allowing C++11 in lldb, we have started using "enum class" instead of straight
+ enums. That is fine for enums that will only ever exist on the lldb_private side of lldb, but err on
+ the side of caution here on't do that for any enums that might find their way into the SB API's, since then
+ you will have to change them so we can get them through SWIG.</li>
+ <p> Also, on a more general note, except when you are using a temporary whose lifespan is not
+ far past its definition, never use one or two character names for ivars. Always use something
+ descriptive, and as far as possible use the same name for the same kind of thing (or the name
+ with an appropriate prefix.) That way if I'm looking at one use of a type, I can search on the
+ variable name and see most of the other uses of the same type of thing. That makes it much easier
+ to get quickly up to speed on how that type should be used.
--- lldb/trunk/www/sidebar.incl (original)
+++ lldb/trunk/www/sidebar.incl Fri Dec 5 17:18:01 2014
@@ -45,6 +45,7 @@
<li><a href="/cpp_reference/html/index.html">C++ API Documentation</a></li>
+ <li><a href="/lldb-coding-conventions.html">Coding Conventions</a></li>
<li><a href="http://llvm.org/bugs">Bug Reports</a></li>
<li><a href="http://llvm.org/svn/llvm-project/lldb/trunk">Browse SVN</a></li>
<li><a href="http://llvm.org/viewvc/llvm-project/lldb/trunk">Browse ViewVC</a></li>
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