CodingStyle - standards while programming for GNU LilyPond

Han-Wen Nienhuys and Jan Nieuwenhuizen



Table of Contents



()

DESCRIPTION

We use these standards while doing programming for GNU LilyPond. If you do some hacking, we appreciate it if you would follow this rules, but if you don't, we still like you.

Functions and methods do not return errorcodes, but use assert for checking status.

A program should be light and agile, its subroutines connected like a string of pearls. The spirit and intent of the program should be retained throughout. There should be neither too little nor too much, neither needless loops nor useless variables, neither lack of structure nor overwhelming rigidity.

A program should follow the 'Law of Least Astonishment'. What is this law? It is simply that the program should always respond to the user in the way that astonishes him least.

A program, no matter how complex, should act as a single unit. The program should be directed by the logic within rather than by outward appearances.

If the program fails in these requirements, it will be in a state of disorder and confusion. The only way to correct this is to rewrite the program.

-- Geoffrey James, "The Tao of Programming"

LANGUAGES

C++, /bin/sh and python are preferred. Perl is not.

FILES

Definitions of classes that are only accessed via pointers (*) or references (&) shall not be included as include files.

filenames


	".hh"	Include files
	".cc"	Implementation files
	".icc"	Inline definition files
	".tcc"	non inline Template defs

in emacs:


	(setq auto-mode-alist
	      (append '(("\\.make$" . makefile-mode)
			("\\.cc$" . c++-mode)
			("\\.icc$" . c++-mode)
			("\\.tcc$" . c++-mode)
			("\\.hh$" . c++-mode)
			("\\.pod$" . text-mode)		
			)
		      auto-mode-alist))

The class Class_name_abbreviation is coded in class-name-abbr.*

INDENTATION

in emacs:


	(add-hook 'c++-mode-hook
		  '(lambda() (c-set-style "gnu")
		     )
		  )

If you like using font-lock, you can also add this to your .emacs:


	(setq font-lock-maximum-decoration t)
	(setq c++-font-lock-keywords-3 
	      (append
	       c++-font-lock-keywords-3
	       '(("\\b\\([a-zA-Z_]+_\\)\\b" 1 font-lock-variable-name-face)
	       ("\\b\\([A-Z]+[a-z_]+\\)\\b" 1 font-lock-type-face))
	       ))

CLASSES and TYPES:


	This_is_a_class
	AClass_name	(for Abbreviation_class_name)

MEMBERS


	Class::member()
	Type Class::member_type_
	Type Class::member_type()

the type is a Hungarian notation postfix for Type. See below

MACROS

Macros should be written completely in uppercase

The code should not be compilable if proper macro declarations are not included.

Don't laugh. It took us a whole evening/night to figure out one of these bugs, because we had a macro that looked like DECLARE_VIRTUAL_FUNCTIONS().

BROKEN CODE

Broken code (hardwired dependencies, hardwired constants, slow algorithms and obvious limitations) should be marked as such: either with a verbose TODO, or with a short "ugh" comment.

COMMENTS

The source is commented in the DOC++ style. Check out doc++ at http://www.zib.de/Visual/software/doc++/index.html


	/*
		C style comments for multiline comments.
		They come before the thing to document.
		[...]
	*/


	/**
		short description.
		Long class documentation.
		(Hungarian postfix)

		TODO Fix boring_member()
	*/
	class Class {
		/**
		  short description.
		  long description
		*/

		Data data_member_;


		/**
			short memo. long doco of member()
			@param description of arguments
			@return Rettype
		*/
		Rettype member(Argtype);

		/// memo only
		boring_member() {
			data_member_ = 121; // ugh
		}
	};

Unfortunately most of the code isn't really documented that good.

MEMBERS (2)

Standard methods:


	///check that *this satisfies its invariants, abort if not.
	void OK() const

	/// print *this (and substructures) to debugging log
	void print() const

	/**
	protected member. Usually invoked by non-virtual XXXX()
	*/
	virtual do_XXXX()

	/**add some data to *this.
	Presence of these methods usually imply that it is not feasible to this
	via  a constructor
	*/
	add (..)

	/// replace some data of *this
	set (..)

Constructor

Every class should have a default constructor.

Don't use non-default constructors if this can be avoided:


	Foo f(1)

is less readable than


	Foo f;
	f.x = 1

or


	Foo f(Foo_convert::int_to_foo (1))

HUNGARIAN NOTATION NAMING CONVENTION

Proposed is a naming convention derived from the so-called Hungarian Notation.

Hungarian

The Hungarian Notation was conceived by or at least got its name from, the hungarian programmer Charles Simonyi. It is a naming convention with the aim to make code more readable (for fellow programmers), and more accessible for programmers that are new to a project.

The essence of the Hungarian Notation is that every identifier has a part which identifies its type (for functions this is the result type). This is particularly useful in object oriented programming, where a particular object implies a specific interface (a set of member functions, perhaps some redefined operators), and for accounting heap allocated memory pointers and links.

Advantages

Another fun quote from Microsoft Secrets:

The Hungarian naming convention gives developers the ability to read other people's code relatively easily, with a minmum number of comments in the source code. Jon De Vann estimated that only about 1 percent of all lines in the Excel product code consist of comments, but the code is still very understandable due to the use of Hungarian: "if you look at our source code, you also notice very few comments. Hungarian gives us the ability to go in and read code..."

Wow! If you use Hungarian you don't have to document your software! Just think of the hours I have wasted documenting while this "silver bullet" existed. I feel so stupid and ashamed! (Didn't MMM-Brooks say `There is no silver bullet?' --HWN)

Disadvantages

  • more keystrokes (disk space!)
  • it looks silly get_slu_p()
  • it looks like code from micro suckers
  • (which) might scare away some (otherwise good?) progammers, or make you a paria in the free software community
  • it has ambiguities
  • not very useful if not used consistently
  • usefullness in very large (but how many classes is very large?) remains an issue.
  • Proposal

  • learn about cut and paste / use emacs or vi or lean to type using ten fingers
  • Use emacs dabbrev-expand, with dabbrev-case-fold-search set to nil.
  • use no, or pick less silly, abbrvs.
  • use non-ambiguous postfixes identifier_name_type_modifier[_modifier]
  • There is no need for Hungarian if the scope of the variable is small, ie. local variables, arguments in function definitions (not declarations).
  • Macros, enums and consts are all uppercase, with the parts of the names separated by underscores.

    Types

    byte
    unsigned char. (The postfix _by is ambiguous)

    b
    bool

    bi
    bit

    ch
    char

    f
    float

    i
    signed integer

    str
    string class

    sz
    Zero terminated c string

    u
    unsigned integer

    User defined types

    
    	/** Slur blah. blah.
    	(slur)
    	*/
    	class Slur {};
    	Slur* slur_p = new Slur;
    
    

    Modifiers

    The following types modify the meaning of the prefix. These are preceded by the prefixes:

    a
    array

    array
    user built array.

    c
    const. Note that the proper order is Type const i.s.o. const Type

    C
    A const pointer. This would be equivalent to _c_l, but since any "const" pointer has to be a link (you can't delete a const pointer), it is superfluous.

    l
    temporary pointer to object (link)

    p
    pointer to newed object

    r
    reference

    Adjective

    Adjectives such as global and static should be spelled out in full. They come before the noun that they refer to, just as in normal english.

    
    foo_global_i: a global variable of type int commonly called "foo".
    
    

    static class members do not need the static_ prefix in the name (the Class::var notation usually makes it clear that it is static)

    descriptio(

    loop_i
    Variable loop: an integer

    u
    Temporary variable: an unsigned integer

    test_ch
    Variable test: a character

    first_name_str
    Variable first_name: a String class object

    last_name_ch_a
    Variable last_name: a char array

    foo_i_p
    Variable foo: an Int* that you must delete

    bar_i_l
    Variable bar: an Int* that you must not delete )

    Generally default arguments are taboo, except for nil pointers.

    The naming convention can be quite conveniently memorised, by expressing the type in english, and abbreviating it

    
    	static Array<int*> foo
    
    

    foo can be described as "the static int-pointer user-array", so you get

    
    	foo_static_l_arr
    
    

    MISCELLANEOUS

    For some tasks, some scripts are supplied, notably creating patches, a mirror of the website, generating the header to put over cc and hh files, doing a release.

    Use them.

    The following generic identifications are used:

    
    	up == 1
    	left == -1
    	right == 1
    	down == -1
    
    

    Intervals are pictured lying on a horizontal numberline (Interval[-1] is the minimum). The 2D plane has +x on the right, +y pointing up.


    Please take me back to the index of LilyPond
    This page was built from lilypond-1.0.0 by


    <janneke@gnu.org>