Define default value to a variable

Question

I want to assign an expression to a variable, and if it has no value, use some default.

On almost every programming language I can use something like:

let linked_hl_id = hlID(l:linked_group) || 114

But of course it does not work, and the option I found is this eyesore using ternary and 2 lines of assignment:

let linked_hl_id = hlID(l:linked_group)
let linked_hl_id = linked_hl_id ? linked_hl_id : 114

What is a better syntax for that? Using NVIM v0.4.4.

Thanks.

Answer 1

Starting from 8.2.1794 vim has null coalescing operator aka falsy operator

let value = somevar ?? othervar ?? 100

:h ??

The expression before the '??' is evaluated.  If it evaluates to
|truthy|, this is used as the result.  Otherwise the expression after the '??'
is evaluated and used as the result.  This is most useful to have a default
value for an expression that may result in zero or empty: >
    echo theList ?? 'list is empty'
    echo GetName() ?? 'unknown'

Neovim uses quite an old vimscript so there is a doubt it would ever have this provided it is focused on lua.

There is also get function that could be used for cases like:

" my_var = g:my_var if it is defined, 100 otherwise
let my_var = get(g:, "my_var", 100)

" my_var = s:my_var if it is defined, 100 otherwise
let my_var = get(s:, "my_var", 100)