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Alex Afanasyev, 04/01/2014 01:52 PM

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# NFD code style guidelines
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NFD adopts [NDN Platform C++, C, C#, Java and JavaScript Code Guidelines](http://named-data.net/codebase/platform/documentation/ndn-platform-development-guidelines/cpp-code-guidelines/), with the following exceptions:
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*   (amended 8) Names representing generic template types should be a single uppercase letter
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        template<class T> ...
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        template<class C, class D> ...
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    However, when template parameter represents a certain concept and expected to have a certain interface, the name should be explicitly spelled out:
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        template<class FaceBase> ...
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        template<class Packet> ...
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*   (amended 10)
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    Global variables should have `g_` prefix
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*   (amended 11)
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    **Private** class variables should have `m_` prefix.
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    **Static** class variables should have `s_` prefix.
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*   (amended 26)
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    Allow commonly used abbreviated **next/prev** pair in addition to **next/previous**
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    Pair **insert/erase** should be used for any new code, already implemented code can keep **insert/delete** if it does not conflict with C++ delete keyword.
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*   (amended 27)
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    In cases when full word is too long, a commonly accepted abbreviation can be used.  For example, **dest** instead of **destination**.
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*   (amended 31)
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    Exceptions can be used in the code, but should be used only in **exceptional** cases and not in the primary processing path.
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    Exceptions can be suffixed with either `Exception` (eg. SecurityException) or `Error` (eg. SecurityError).  Alternatively (and it is a recommended method), one should declare exception class `Exception` or `Error` as an inner class, from which the exception is thrown. For example, when declaring class Foo that can throw errors, one can write the following:
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        #include <stdexcept>
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        class Foo
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        {
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          class Error : std::runtime_exception
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          {
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          public:
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            explicit
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            Error(const std::string& what)
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              : std::runtime_error(what)
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            {
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            }
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          };
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        };  
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    In addition to that, if class Foo is a base class or interface for some class hierarchy, then child classes should should define their own `Error` or `Exception` classes that are inherited from the parent's Error class.
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*   (amended 33)
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    We will use only `.cpp` and `.hpp` extensions
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*   (removed 35)
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    Lines should be within a reasonable range. Lines longer than 100 columns should generally be avoided.
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*   (updated 37)
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    Exceptions:
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    * The following is the standard practice with ``operator<<``:
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            std::cout << "Something here "
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                      << "Something there" << std::endl;
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*   (removed 44)
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    Implicit conversion is generally allowed.
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    Implicit conversion between integer and floating point numbers can cause problems and should be avoided.
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    Implicit conversion in single-argument constructor is usually undesirable. Therefore, all single-argument constructors should be marked 'explicit', unless implicit conversion is desirable. In that case, a comment should document the reason.
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    Avoid C-style casts.  Use `static_cast`, `dynamic_cast`, `reinterpret_cast`, `const_cast` instead where appropriate.
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*   (replaced 48)
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    In most cases, class instance variables should never be declared public.
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    The concepts of information hiding and encapsulation are violated by public variables. Use private variables and access methods instead. One exception to this rule is when the class is essentially a dumb data structure with no behavior (equivalent to a C struct, also known as PODS).  In this case it is appropriate to make the instance variables public by using ``struct``.
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*   (amended 68)
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    All three presented styles ARE acceptable.  First and third ARE recommended (these are actually GNU styles).
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*   (amended 69)
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    The class declarations should have the following form:
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        class SomeClass : public BaseClass 
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        { 
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        public: 
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          ... <public methods> ...
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        protected: 
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          ... <protected methods> ...
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        private: 
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          ... <private methods> ...
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        public: 
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          ... <public data> ...
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        protected: 
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          ... <protected data> ...
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        private: 
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          ... <private data> ...
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        };
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    ``public``, ``protected``, ``private`` may be repeated several times without interleaving (e.g. public, public, public, private, private) if this allows better readability of the code.
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*   (amended 70)
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    When declaring/defining function/method, the return type should be put on a separate line before function/method name.
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    Method and function definitions should have the following form:
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        void
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        someMethod() 
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        { 
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          ... 
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        }
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*   (amended 76) No space requirement before : in switch statements
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        switch (condition) { 
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          case ABC:
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            statements; 
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            // Fallthrough 
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          case DEF: 
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            statements; 
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            break;
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          case XYZ: 
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            statements; 
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            break; 
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          default: 
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            statements; 
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            break;
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        }    
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## Python addition
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Most of the provisions in the above style guidance apply to Python as well.  For python-specific elements, [PEP 8](http://legacy.python.org/dev/peps/pep-0008/) can be used as a reference coding style.  
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The following is few rules directly adopted from [PEP 8](http://legacy.python.org/dev/peps/pep-0008/):
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* **P1**  Always surround these binary operators with a single space on either side: assignment (=), augmented assignment (+=, -= etc.), comparisons (==, <, >, !=, <>, <=, >=, in, not in, is, is not), Booleans (and, or, not).
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        def complex(real, imag=0.0):
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            value = 1.1
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            return magic(r=real + value, i=imag)
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* **P2** Don't use spaces around the = sign when used to indicate a keyword argument or a default parameter value.
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        def complex(real, imag=0.0):
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            return magic(r=real, i=imag)