> :let {var} ?= {expr} This is a conditional variable
assignment operator,
> it only has an effect if the variable
is not yet
> defined. This statement:
>
> let foo ?= "bar"
>
> is exactly equivalent to this:
>
> if !exists("foo")
> let foo = "bar"
> endif
Along those lines, why not define a conditional attribute that would
apply to functions?
:fu[nction][!?] {name}([arguments]) [range] [abort] [dict]
...
When a function by this name already exists and
[!] or
[?] is not used an error message is given. When [!]
is
used, an existing function is silently replaced; when
[?] is used, the function is ignored.
The same goes for :command[?]
