2016-04-20 12:35 GMT+03:00 Bram Moolenaar <[email protected]>:
>
> Bjorn Linse wrote:
>
>> > Internally a list with a NULL pointer is supposed to be handled like an
>> > empty list. This is efficient, but tricky. Nikolai just sent a patch,
>> > hopefully that helps.
>>
>> Good, but I wonder if it is not better for getreg("a",1,1) to always
>> return a mutable list (an empty mutable list in this case)? Because as
>> it returns a mutable list for a register with contents (
>> setreg("a",'x') ) or an empty one ( setreg("a",'') ) a plugin writer
>> might come to expect that it always returns a fresh mutable list, but
>> this then fails for an undefined register ( setreg("a",[]) ). Isn't
>> API consistency better that a little bit of efficiency, in this case?
>
> The NULL is supposed to be the same as an empty, mutable list. This is
> tricky, because code that expects a list needs to check for the NULL and
> create the list if needed.
This really cannot be mutable. In many cases all function has is
typval_T* pointing to a copy of typval_T that is allocated on a stack:
e.g. `func_call` does this. Obviously changes to such typval_T* do not
affect what is stored in tho original variable. I guess fixing this
will be a major refactoring.
In addition to this
let foo = v:_null_list
let bar = foo
call add(foo, 1)
What should `bar` contain? If it is mutable empty list then it should
contain `[1]` like in
let foo = []
let bar = foo
call add(foo, 1)
but how you are going to implement this with NULL list?
>
> An alternative would be to create an empty list instead of using a NULL.
> However, that requires memory allocation and there will still always be
> the chance of getting a NULL anyway (out of memory, mistake in the code).
>
> We could also consider NULL and invalid list, but I would think that
> puts the burden on the script writer.
>
> --
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>
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