*develop.txt* For Vim version 5.6. Last change: 2000 Jan 01 VIM REFERENCE MANUAL by Bram Moolenaar Development of Vim. *development* This text is important for those who want to be involved in further developing Vim. 1. Design goals |design-goals| 2. Coding style |coding-style| ============================================================================== 1. Design goals *design-goals* Most important things come first (roughly). Note that quite a few items are contradicting. This is intentional. A balance must be found between them. VIM IS... VI COMPATIBLE *design-compatible* First of all, it should be possible to use Vim as a drop-in replacement for Vi. When the user wants to, he can use Vim in compatible mode and hardly notice any difference with the original Vi. Exceptions: - We don't reproduce obvious Vi bugs in Vim. - There are different versions of Vi. I am using Version 3.7 (6/7/85) as a reference. But support for other versions is also included when possible. The Vi part of POSIX is not considered a definitive source. - Vim adds new commands, you cannot rely on some command to fail because it didn't exist in Vi. - Vim will have a lot of features that Vi doesn't have. Going back from Vim to Vi will be a problem, this cannot be avoided. - Some things are hardly ever used (open mode, sending an e-mail when crashing, etc.). Those will only be included when someone has a good reason why it should be included and it's not too much work. - For some items it is debatable whether Vi compatibility should be maintained. There will be an option flag for these. VIM IS... IMPROVED *design-improved* The IMproved bits of Vim should make it a better Vi, without becoming a completely different editor. Extensions are done with a "Vi spirit". - Use the keyboard as much as feasible. The mouse requires a third hand, which we don't have. Many terminals don't have a mouse. - When the mouse is used anyway, avoid the need to switch back to the keyboard. Avoid mixing mouse and keyboard handling. - Add commands and options in a consistent way. Otherwise people will have a hard time finding and remembering them. Keep in mind that more commands and options will be added later. - A feature that people do not know about is a useless feature. Don't add obscure features, or at least add hints in documentation that they exists. - Minimize using CTRL and other modifiers, they are more difficult to type. - There are many first-time and inexperienced Vim users. Make it easy for them to start using Vim and learn more over time. - There is no limit to the features that can be added. Selecting new features is one based on (1) what users ask for, (2) how much effort it takes to implement and (3) someone actually implementing it. VIM IS... MULTI PLATFORM *design-multi-platform* Vim tries to help as many users on as many platforms as possible. - Support many kinds of terminals. The minimal demands are cursor positioning and clear-screen. Commands should only use key strokes that most keyboards have. Support all the keys on the keyboard for mapping. - Support many platforms. A condition is that there is someone willing to do Vim development on that platform, and it doesn't mean messing up the code. - Support many compilers and libraries. Not everybody is able or allowed to install another compiler or GUI library. - People switch from one platform to another, and from GUI to terminal version. Features should be present in all versions, or at least in as many as possible with a reasonable effort. Try to avoid that users must switch between platforms to accomplish their work efficiently. - That a feature is not possible on some platforms, or only possible on one platform, does not mean it cannot be implemented. [This intentionally contradicts the previous item, these two must be balanced.] VIM IS... WELL DOCUMENTED *design-documented* - A feature that isn't documented is a useless feature. A patch for a new feature must include the documentation. - Documentation should be comprehensive and understandable. Using examples is recommended. - Don't make the text unnecessarily long. Less documentation means that an item is easier to find. VIM IS... HIGH SPEED AND SMALL IN SIZE *design-speed-size* Using Vim must not be a big attack on system resources. Keep it small and fast. - Computers are becoming faster and bigger each year. Vim can grow too, but no faster than computers are growing. Keep Vim usable on older systems. - Many users start Vim from a shell very often. Startup time must be short. - Commands must work efficient. The time they consume must be as small as possible. Useful commands may take longer. - Don't forget that some people use Vim over a slow connection. Minimize the communication overhead. - Items that add considerably to the size and are not used by many people should be a feature that can be disabled. - Vim is a component among other components. Don't turn it into a massive application, but have it work well together with other programs. VIM IS... MAINTAINABLE *design-maintain* - The source code should not become a mess. It should be reliable code. - Use the same layout in all files to make it easy to read |coding-style|. - Use comments in a useful way! - Porting to another platform should be made easy, without having to change too much platform-independent code. - Use the object-oriented spirit: Put data and code together. Minimize the knowledge spread to other parts of the code. VIM IS... FLEXIBLE *design-flexible* Vim should make it easy for users to work in their preferred styles rather than coercing its users into particular patterns of work. This can be for items with a large impact (e.g., the 'compatible' option) or for details. The defaults are carefully chosen such that most users will enjoy using Vim as it is. Commands and options can be used to adjust Vim to the desire of the user and its environment. VIM IS... NOT *design-not* - Vim is not a shell or an Operating System. You will not be able to run a shell inside Vim or use it to control a debugger. This should work the other way around: Use Vim as a component from a shell or in an IDE. - Vim is not a fancy GUI editor that tries to look nice at the cost of being less consistent over all platforms. But functional GUI features are welcomed. ============================================================================== 2. Coding style *coding-style* These are the rules to use when making changes to the Vim source code. Please stick to these rules, to keep the sources readable and maintainable. This list is not complete. Look in the source code for more examples. MAKING CHANGES *style-changes* The basic steps to make changes to the code: 1. Adjust the documentation. Doing this first gives you an impression of how your changes affect the user. 2. Make the source code changes. 3. Check ../doc/todo.txt if the change affects any listed item. 4. Make a patch with "diff -c" against the unmodified code and docs. 5. Make a note about what changed and include it with the patch. USE OF COMMON FUNCTIONS *style-functions* Some functions that are common to use, have a special Vim version. Always consider using the Vim version, because they were introduced with a reason. NORMAL NAME VIM NAME DIFFERENCE OF VIM VERSION free() vim_free() Checks for freeing NULL malloc() alloc() Checks for out of memory situation malloc() lalloc() Like alloc(), but has long argument strcpy() STRCPY() Includes cast to (char *), for char_u * args strchr() vim_strchr() Accepts special characters strrchr() vim_strrchr() Accepts special characters isspace() vim_isspace() Can handle characters > 128 iswhite() vim_iswhite() Only TRUE for Tab and space memcpy() vim_memmove() Handles overlapped copies bcopy() vim_memmove() Handles overlapped copies memset() vim_memset() Uniform for all systems NAMES *style-names* Because of the requirement that Vim runs on as many systems as possible, we need to avoid using names that are already defined by the system. This is a list of names that are known to cause trouble. The name is given as a regexp pattern. is.*() POSIX, ctype.h to.*() POSIX, ctype.h d_.* POSIX, dirent.h l_.* POSIX, fcntl.h gr_.* POSIX, grp.h pw_.* POSIX, pwd.h sa_.* POSIX, signal.h mem.* POSIX, string.h str.* POSIX, string.h wcs.* POSIX, string.h st_.* POSIX, stat.h tms_.* POSIX, times.h tm_.* POSIX, time.h c_.* POSIX, termios.h MAX.* POSIX, limits.h __.* POSIX, system _[A-Z].* POSIX, system E[A-Z0-9]* POSIX, errno.h wait don't use as argument to a function, conflicts with types.h index shadows global declaration time shadows global declaration new C++ reserved keyword try Borland C++ doesn't like it to be used as a variable. basename() GNU string function dirname() GNU string function get_env_value() Linux system function VARIOUS *style-various* Don't use '\"', some compilers can't handle it. '"' works fine. Don't use: #if HAVE_SOME Some compilers can't handle that and complain that "HAVE_SOME" is not defined. Use #ifdef HAVE_SOME or #if defined(HAVE_SOME) STYLE *style-examples* General rule: One statement per line. Wrong: if (cond) a = 1; OK: if (cond) a = 1; Wrong: while (cond); OK: while (cond) ; Wrong: do a = 1; while (cond); OK: do a = 1; while (cond); Functions start with: Wrong: int function_name(int arg1, int arg2) OK: /* * Explanation of what this function is used for. * * Return value explanation. */ int function_name(arg1, arg2) int arg1; /* short comment about arg1 */ int arg2; /* short comment about arg2 */ { int local; /* comment about local */ local = arg1 * arg2; NOTE: Don't use ANSI style function declarations. A few people still have to use a compiler that doesn't support it. SPACES AND PUNCTUATION *style-spaces* No space between a function name and the bracket: Wrong: func (arg); OK: func(arg); Do use a space after if, while, switch, etc. Wrong: if(arg) for(;;) OK: if (arg) for (;;) Use a space after a comma and semicolon: Wrong: func(arg1,arg2); for (i = 0;i < 2;++i) OK: func(arg1, arg2); for (i = 0; i < 2; ++i) Use a space before and after '=', '+', '/', etc. Wrong: var=a*5; OK: var = a * 5; In general: Use empty lines to group lines of code together. Put a comment just above the group of lines. This makes it more easy to quickly see what is being done. OK: /* Prepare for building the table. */ get_first_item(); table_idx = 0; /* Build the table */ while (has_item()) table[table_idx++] = next_item(); /* Finish up. */ cleanup_items(); generate_hash(table); vim:tw=78:ts=8:sw=8: