Mercurial > vim
comparison runtime/doc/eval.txt @ 16615:1a911bd57f11 v8.1.1310
patch 8.1.1310: named function arguments are never optional
commit https://github.com/vim/vim/commit/42ae78cfff171fbd7412306083fe200245d7a7a6
Author: Bram Moolenaar <Bram@vim.org>
Date: Thu May 9 21:08:58 2019 +0200
patch 8.1.1310: named function arguments are never optional
Problem: Named function arguments are never optional.
Solution: Support optional function arguments with a default value. (Andy
Massimino, closes #3952)
| author | Bram Moolenaar <Bram@vim.org> |
|---|---|
| date | Thu, 09 May 2019 21:15:05 +0200 |
| parents | 1eaf34420bb3 |
| children | 4790302965fc |
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| 16614:306acde1a598 | 16615:1a911bd57f11 |
|---|---|
| 10918 However, if a composite type is used, such as |List| or |Dictionary| , you can | 10918 However, if a composite type is used, such as |List| or |Dictionary| , you can |
| 10919 change their contents. Thus you can pass a |List| to a function and have the | 10919 change their contents. Thus you can pass a |List| to a function and have the |
| 10920 function add an item to it. If you want to make sure the function cannot | 10920 function add an item to it. If you want to make sure the function cannot |
| 10921 change a |List| or |Dictionary| use |:lockvar|. | 10921 change a |List| or |Dictionary| use |:lockvar|. |
| 10922 | 10922 |
| 10923 When not using "...", the number of arguments in a function call must be equal | |
| 10924 to the number of named arguments. When using "...", the number of arguments | |
| 10925 may be larger. | |
| 10926 | |
| 10927 It is also possible to define a function without any arguments. You must | 10923 It is also possible to define a function without any arguments. You must |
| 10928 still supply the () then. | 10924 still supply the () then. |
| 10929 | 10925 |
| 10930 It is allowed to define another function inside a function body. | 10926 It is allowed to define another function inside a function body. |
| 10927 | |
| 10928 *optional-function-argument* | |
| 10929 You can provide default values for positional named arguments. This makes | |
| 10930 them optional for function calls. When a positional argument is not | |
| 10931 specified at a call, the default expression is used to initialize it. | |
| 10932 This only works for functions declared with |function|, not for lambda | |
| 10933 expressions |expr-lambda|. | |
| 10934 | |
| 10935 Example: > | |
| 10936 function Something(key, value = 10) | |
| 10937 echo a:key .. ": " .. value | |
| 10938 endfunction | |
| 10939 call Something('empty') "empty: 10" | |
| 10940 call Something('key, 20) "key: 20" | |
| 10941 | |
| 10942 The argument default expressions are evaluated at the time of the function | |
| 10943 call, not definition. Thus it is possible to use an expression which is | |
| 10944 invalid the moment the function is defined. The expressions are are also only | |
| 10945 evaluated when arguments are not specified during a call. | |
| 10946 | |
| 10947 You can pass |v:none| to use the default expression. Note that this means you | |
| 10948 cannot pass v:none as an ordinary value when an argument has a default | |
| 10949 expression. | |
| 10950 | |
| 10951 Example: > | |
| 10952 function Something(a = 10, b = 20, c = 30) | |
| 10953 endfunction | |
| 10954 call Something(1, v:none, 3) " b = 20 | |
| 10955 < | |
| 10956 *E989* | |
| 10957 Optional arguments with default expressions must occur after any mandatory | |
| 10958 arguments. You can use "..." after all optional named arguments. | |
| 10959 | |
| 10960 It is possible for later argument defaults to refer to prior arguments, | |
| 10961 but not the other way around. They must be prefixed with "a:", as with all | |
| 10962 arguments. | |
| 10963 | |
| 10964 Example that works: > | |
| 10965 :function Okay(mandatory, optional = a:mandatory) | |
| 10966 :endfunction | |
| 10967 Example that does NOT work: > | |
| 10968 :function NoGood(first = a:second, second = 10) | |
| 10969 :endfunction | |
| 10970 < | |
| 10971 When not using "...", the number of arguments in a function call must be equal | |
| 10972 to the number of mandatory named arguments. When using "...", the number of | |
| 10973 arguments may be larger. | |
| 10931 | 10974 |
| 10932 *local-variables* | 10975 *local-variables* |
| 10933 Inside a function local variables can be used. These will disappear when the | 10976 Inside a function local variables can be used. These will disappear when the |
| 10934 function returns. Global variables need to be accessed with "g:". | 10977 function returns. Global variables need to be accessed with "g:". |
| 10935 | 10978 |