if error then do the or

[RizbIT]

if you have a list and you run find value and nothing is found can you just add an or to set a value

for example can you do this
var dbid = ds_list_find_value(list1,1) or 0;

so if value list position 1 is undefined then it will set var dbid as 0 ?

 

[CloseRange]

I belive just do this:

var dbid = ds_list_find_value(list1, 1);
if (is_undefined(dblid)) {
    ds_list_replace(list1, 1, 0);
    dblid = 0;
}

 

[RizbIT]

i know but im just looking at abreviating code you know..

 

[CloseRange]

hmm no I don't belive you can get simpler than that unless you are using gm2 by using ternary operators:

var dbid = ds_list_find_value(list1, 1);
      dbid = is_undefined(dbid) ? 0 : dbid;

except that code will not actually set the value in ds_list to 0.
so it's the equivalent to writing:

var dbid = ds_list_find_value(list1, 1);
if (is_undefined(dblid)) dblid = 0;

If you do need to perform this kind of check a lot then I'd suggest writing a function:

/// list_find_alternate(list, pos, default);
var r = ds_list_find_value(argument[0], argument[1]);
if(is_undefined(r)) return argument[2];
return r;

then you can call it like so:

var dbid = list_find_alternate(list1, 1, 0);

a nice 1 liner

 

[FrostyCat]

There are 3 issues with the is_undefined() solution:

• It's possible to synthetically insert undefined into a list.
• The Manual's entry on ds_list_find_value() states that 0 can sometimes be returned for out-of-bound entries.
• There have been several cases in the past of crashes on isolated exports when accessing data structures beyond bounds.

If you want to genuinely check for the out-of-bounds case, I would recommend ds_list_size(). This is perfectly stable and well-defined behaviour that has never been broken in GMS 2 history, unlike checking for undefined.

var dbid = (ds_list_size(list1) <= 1) ? 0 : list1[| 1];

On a related note, this is why I also discourage the related form below on maps for checking if a key isn't in it:

// Don't do this for checking the absence of a key
if (is_undefined(map1[? "key"])) {
  ...
}

The best-practice solution is to check ds_map_exists() instead.

// Do this instead
if (!ds_map_exists(map1, "key")) {
  ...
}

 

[RizbIT]

im trying to understand or see if using non standard (for me...) syntax in coding will make sense or things easier

for example you wrote
(is_undefined(map1[? "key"]

no what does the ? mean, why is it there, thats something id never use, however im sure it simplifies coding syntax so this is what my question ispartly about.

maybe theres a section in help file but what do i search for? 'ternary operators' ?

 

[rIKmAN]

maybe theres a section in help file but what do i search for? 'ternary operators' ?

Yeah, and accessors.