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*usr_50.txt* For Vim version 9.1. Last change: 2022 Jun 20 VIM USER MANUAL - by Bram Moolenaar Advanced Vim script writing |50.1| Exceptions |50.2| Function with variable number of arguments |50.3| Restoring the view Next chapter: |usr_51.txt| Create a plugin Previous chapter: |usr_45.txt| Select your language (local) Table of contents: |usr_toc.txt| ============================================================================== *50.1* Exceptions Let's start with an example: > try read ~/templates/pascal.tmpl catch /E484:/ echo "Sorry, the Pascal template file cannot be found." endtry The `read` command will fail if the file does not exist. Instead of generating an error message, this code catches the error and gives the user a message with more information. For the commands in between `try` and `endtry` errors are turned into exceptions. An exception is a string. In the case of an error the string contains the error message. And every error message has a number. In this case, the error we catch contains "E484:". This number is guaranteed to stay the same (the text may change, e.g., it may be translated). Besides being able to give a nice error message, Vim will also continue executing commands after the `:endtry`. Otherwise, once an uncaught error is encountered, execution of the script/function/mapping will be aborted. When the `read` command causes another error, the pattern "E484:" will not match in it. Thus this exception will not be caught and result in the usual error message and execution is aborted. You might be tempted to do this: > try read ~/templates/pascal.tmpl catch echo "Sorry, the Pascal template file cannot be found." endtry This means all errors are caught. But then you will not see an error that would indicate a completely different problem, such as "E21: Cannot make changes, 'modifiable' is off". Think twice before you catch any error! Another useful mechanism is the `finally` command: > var tmp = tempname() try exe ":.,$write " .. tmp exe "!filter " .. tmp :.,$delete exe ":$read " .. tmp finally delete(tmp) endtry This filters the lines from the cursor until the end of the file through the "filter" command, which takes a file name argument. No matter if the filtering works, if something goes wrong in between `try` and `finally` or the user cancels the filtering by pressing CTRL-C, the `delete(tmp)` call is always executed. This makes sure you don't leave the temporary file behind. The `finally` does not catch the exception, the error will still abort further execution. More information about exception handling can be found in the reference manual: |exception-handling|. ============================================================================== *50.2* Function with variable number of arguments Vim enables you to define functions that have a variable number of arguments. The following command, for instance, defines a function that must have 1 argument (start) and can have up to 20 additional arguments: > def Show(start: string, ...items: list<string>) The variable "items" will be a list in the function containing the extra arguments. You can use it like any list, for example: > def Show(start: string, ...items: list<string>) echohl Title echo "start is " .. start echohl None for index in range(len(items)) echon $" Arg {index} is {items[index]}" endfor echo enddef You can call it like this: > Show('Title', 'one', 'two', 'three') < start is Title Arg 0 is one Arg 1 is two Arg 2 is three ~ This uses the `echohl` command to specify the highlighting used for the following `echo` command. `echohl None` stops it again. The `echon` command works like `echo`, but doesn't output a line break. If you call it with one argument the "items" list will be empty. `range(len(items))` returns a list with the indexes, what `for` loops over, we'll explain that further down. ============================================================================== *50.3* Restoring the view Sometimes you want to jump around, make a change and then go back to the same position and view. For example to change something in the file header. This can be done with two functions: > var view = winsaveview() # Move around, make changes winrestview(view) ============================================================================== Next chapter: |usr_51.txt| Create a plugin Copyright: see |manual-copyright| vim:tw=78:ts=8:noet:ft=help:norl: