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Update C++ style guide to 3.170:
- Allow overloading a function judiciously. - _unittest and _regtest are deprecated. - Document C++0x policy. - Allow namespace aliases in .h files when inside namespaces. - Give examples for and against parentheses with return. - Update set of allowed Boost headers. - Add a caveat to the forward-declaration section, mentioning impicit constructors.
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cppguide.xml
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cppguide.xml
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@ -4,7 +4,7 @@
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<p align="right">
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Revision 3.161
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Revision 3.170
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</p>
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@ -148,7 +148,7 @@ Tashana Landray
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<STYLEPOINT title="Header File Dependencies">
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<SUMMARY>
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Don't use an <code>#include</code> when a forward declaration
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would suffice.
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would suffice.
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</SUMMARY>
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<BODY>
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<p>
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@ -178,7 +178,13 @@ Tashana Landray
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<code>Foo&</code>.
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</li>
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<li> We can declare (but not define) functions with arguments,
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and/or return values, of type <code>Foo</code>.
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and/or return values, of type <code>Foo</code>. (One
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exception is if an argument <code>Foo</code>
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or <code>const Foo&</code> has a
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non-<code>explicit</code>, one-argument constructor,
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in which case we need the full definition to support
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automatic type conversion.)
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</li>
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<li> We can declare static data members of type
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<code>Foo</code>. This is because static data members
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@ -386,7 +392,7 @@ Tashana Landray
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<p>
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<code><var>dir/foo</var>.cc</code> and
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<code><var>dir2/foo2</var>.h</code> are often in the same
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directory (e.g. <code>base/basictypes_unittest.cc</code> and
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directory (e.g. <code>base/basictypes_test.cc</code> and
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<code>base/basictypes.h</code>), but can be in different
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directories too.
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</p>
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@ -581,13 +587,35 @@ Tashana Landray
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</li>
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<li> Namespace aliases are allowed anywhere in a
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<code>.cc</code> file, and in functions and methods in
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<code>.h</code> files.
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<code>.cc</code> file, anywhere inside the named
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namespace that wraps an entire <code>.h</code> file,
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and in functions and methods.
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<CODE_SNIPPET>
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// OK in .cc files.
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// Must be in a function or method in .h files.
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// Shorten access to some commonly used names in .cc files.
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namespace fbz = ::foo::bar::baz;
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// Shorten access to some commonly used names (in a .h file).
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namespace librarian {
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// The following alias is avaliable to all files including
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// this header (in namespace librarian):
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// alias names should therefore be chosen consistently
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// within a project.
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namespace pd_s = ::pipeline_diagnostics::sidetable;
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inline void my_inline_function() {
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// namespace alias local to a function (or method).
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namespace fbz = ::foo::bar::baz;
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...
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}
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} // namespace librarian
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</CODE_SNIPPET>
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<p>
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Note that an alias in a .h file is visible to everyone
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#including that file, so public headers (those available
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outside a project) and headers transitively #included by them,
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should avoid defining aliases, as part of the general
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goal of keeping public APIs as small as possible.
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</p>
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</li>
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</ul>
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</SUBSECTION>
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@ -1474,7 +1502,7 @@ Tashana Landray
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<BODY>
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<p>
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<code>cpplint.py</code>
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is a tool that reads a source file and
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is a tool that reads a source file and
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identifies many style errors. It is not perfect, and has both false
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positives and false negatives, but it is still a valuable tool. False
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positives can be ignored by putting <code>// NOLINT</code> at
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@ -1547,10 +1575,10 @@ Tashana Landray
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<STYLEPOINT title="Function Overloading">
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<SUMMARY>
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Use overloaded functions (including constructors) only in cases
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where input can be specified in different types that contain the
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same information. Do not use function overloading to simulate
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<A HREF="#Default_Arguments">default function parameters</A>.
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Use overloaded functions (including constructors) only if a
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reader looking at a call site can get a good idea of what is
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happening without having to first figure out exactly which
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overload is being called.
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</SUMMARY>
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<BODY>
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<DEFINITION>
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@ -1574,20 +1602,18 @@ Tashana Landray
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convenient for Visitors.
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</PROS>
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<CONS>
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One reason to minimize function overloading is that
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overloading can make it hard to tell which function is being
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called at a particular call site. Another one is that most
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people are confused by the semantics of inheritance if a
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deriving class overrides only some of the variants of a
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function. Moreover, reading client code of a library may
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become unnecessarily hard because of all the reasons against
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<A HREF="#Default_Arguments">default function parameters</A>.
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If a function is overloaded by the argument types alone, a
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reader may have to understand C++'s complex matching rules in
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order to tell what's going on. Also many people are confused
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by the semantics of inheritance if a derived class overrides
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only some of the variants of a function.
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</CONS>
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<DECISION>
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If you want to overload a function, consider qualifying the
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name with some information about the arguments, e.g.,
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<code>AppendString()</code>, <code>AppendInt()</code> rather
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than just <code>Append()</code>.
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</DECISION>
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</BODY>
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</STYLEPOINT>
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@ -2517,40 +2543,97 @@ Tashana Landray
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techniques, and an excessively "functional" style of programming.
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</CONS>
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<DECISION>
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In order to maintain a high level of readability for all contributors
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who might read and maintain code, we only allow an approved subset of
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Boost features. Currently, the following libraries are permitted:
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<ul>
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<li> <a href="http://www.boost.org/libs/utility/call_traits.htm">
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Call Traits</a> from <code>boost/call_traits.hpp</code>
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</li>
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<li> <a href="http://www.boost.org/libs/utility/compressed_pair.htm">
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Compressed Pair</a> from <code>boost/compressed_pair.hpp</code>
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</li>
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<li> <a href="http://www.boost.org/libs/ptr_container/">
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Pointer Container</a> from <code>boost/ptr_container</code> except serialization
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</li>
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<li> <a href="http://www.boost.org/libs/array/">
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Array</a> from <code>boost/array.hpp</code>
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</li>
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<li> <a href="http://www.boost.org/libs/graph/">
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The Boost Graph Library (BGL)</a> from <code>boost/graph</code> except serialization
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</li>
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<li> <a href="http://www.boost.org/libs/property_map/">
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Property Map</a> from <code>boost/property_map.hpp</code>
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</li>
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<li> The part of
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<a href="http://www.boost.org/libs/iterator/">
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Iterator</a> that deals with defining iterators:
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<code>boost/iterator/iterator_adaptor.hpp</code>,
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<code>boost/iterator/iterator_facade.hpp</code>, and
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<code>boost/function_output_iterator.hpp</code></li>
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</ul>
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We are actively considering adding other Boost features to the list, so
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this rule may be relaxed in the future.
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<div>
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In order to maintain a high level of readability for all contributors
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who might read and maintain code, we only allow an approved subset of
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Boost features. Currently, the following libraries are permitted:
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<ul>
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<li> <a href="http://www.boost.org/libs/utility/call_traits.htm">
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Call Traits</a> from <code>boost/call_traits.hpp</code>
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</li>
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<li> <a href="http://www.boost.org/libs/utility/compressed_pair.htm">
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Compressed Pair</a> from <code>boost/compressed_pair.hpp</code>
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</li>
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<li> <a href="http://www.boost.org/libs/ptr_container/">
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Pointer Container</a> from <code>boost/ptr_container</code> except
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serialization and wrappers for containers not in the C++03
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standard (<code>ptr_circular_buffer.hpp</code> and
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<code>ptr_unordered*</code>)
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</li>
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<li> <a href="http://www.boost.org/libs/array/">
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Array</a> from <code>boost/array.hpp</code>
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</li>
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<li> <a href="http://www.boost.org/libs/graph/">
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The Boost Graph Library (BGL)</a> from <code>boost/graph</code>,
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except serialization (<code>adj_list_serialize.hpp</code>) and
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parallel/distributed algorithms and data structures
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(<code>boost/graph/parallel/*</code> and
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<code>boost/graph/distributed/*</code>).
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</li>
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<li> <a href="http://www.boost.org/libs/property_map/">
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Property Map</a> from <code>boost/property_map</code>, except
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parallel/distributed property maps
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(<code>boost/property_map/parallel/*</code>).
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</li>
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<li> The part of
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<a href="http://www.boost.org/libs/iterator/">
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Iterator</a> that deals with defining iterators:
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<code>boost/iterator/iterator_adaptor.hpp</code>,
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<code>boost/iterator/iterator_facade.hpp</code>, and
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<code>boost/function_output_iterator.hpp</code></li>
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</ul>
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We are actively considering adding other Boost features to the list, so
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this rule may be relaxed in the future.
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</div>
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</DECISION>
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</BODY>
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</STYLEPOINT>
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<STYLEPOINT title="C++0x">
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<SUMMARY>
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Use only approved libraries and language extensions from C++0x.
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Currently, none are approved.
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</SUMMARY>
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<BODY>
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<DEFINITION>
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C++0x is the next ISO C++ standard, currently in
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<a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3092.pdf">final
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committee draft</a> form. It contains
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<a href="http://en.wikipedia.org/wiki/C%2B%2B0x">significant
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changes</a> both to the language and libraries.
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</DEFINITION>
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<PROS>
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We expect that C++0x will become the next standard, and eventually will
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be supported by most C++ compilers. It standardizes some common C++
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extensions that we use already, allows shorthands for some operations,
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and has some safety improvements.
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</PROS>
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<CONS>
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<p>
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The C++0x standard is substantialy more complex than its predecessor
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(1,300 pages versus 800 pages), and is
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unfamilar to many developers. The long-term effects of some
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features on code readability and maintenance are unknown. We cannot
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predict when its various features will be implemented uniformly by
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tools that may be of interest (gcc, icc, clang, Eclipse, etc.).
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</p>
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<p>
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As with <a href="#Boost">Boost</a>, some C++0x extensions encourage
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coding practices that hamper readability—for example by removing
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checked redundancy (such as type names) that may be helpful to readers,
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or by encouraging template metaprogramming. Other extensions
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duplicate functionality available through existing
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mechanisms, which may lead to
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confusion and conversion costs.
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</p>
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</CONS>
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<DECISION>
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Use only C++0x libraries and language features that have been approved
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for use. Currently, no such features are approved.
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Features will be approved individually as appropriate.
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</DECISION>
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</BODY>
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</STYLEPOINT>
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@ -2665,6 +2748,7 @@ Tashana Landray
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my_useful_class.cc<br/>
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my-useful-class.cc<br/>
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myusefulclass.cc<br/>
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myusefulclass_test.cc // _unittest and _regtest are deprecated.<br/>
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</code>
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</p>
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<p>
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@ -3942,15 +4026,23 @@ Tashana Landray
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<STYLEPOINT title="Return Values">
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<SUMMARY>
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Do not surround the <code>return</code> expression with parentheses.
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Do not needlessly surround the <code>return</code> expression with
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parentheses.
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</SUMMARY>
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<BODY>
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<p>
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Return values should not have parentheses:
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Use parentheses in <code>return expr;</code> only where you would use
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them in <code>x = expr;</code>.
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</p>
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<CODE_SNIPPET>
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return x; // not return(x);
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return result; // No parentheses in the simple case.
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return (some_long_condition && // Parentheses ok to make a complex
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another_condition); // expression more readable.
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</CODE_SNIPPET>
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<BAD_CODE_SNIPPET>
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return (value); // You wouldn't write var = (value);
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return(result); // return is not a function!
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</BAD_CODE_SNIPPET>
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</BODY>
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</STYLEPOINT>
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@ -4422,7 +4514,7 @@ Tashana Landray
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<HR/>
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<p align="right">
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Revision 3.161
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Revision 3.170
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</p>
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