Tab completion of struct within cell

Hello together,

I am working on a large object-oriented database where it happens that I store structs or instances of classes within a cell. However, I experience that the autocomplete or tab completion function of Matlab does not work anymore after the cell. So, for example I define a struct "structTest":

structTest.a = 2;
structTest.b = 4;

The autocompletion works fine:

Now I save this struct within the cell "cellTest":

cellTest = cell(2,1);
cellTest{1,1} = structTest;

Unfortunately, the autocompletion does not work anymore:

Similarly, the problem occurs when I save instances of classes within a cell.

After reading about .json files for tab completion of functions and overriding the properties(obj) function in the class definition with fieldnames(obj), I still don't have a clue on how to deal with this. Especially since fieldnames(cellTest{1,1}) works just fine:

>> fieldnames(cellTest{1,1})

ans =

  2×1 cell array

    {'a'}
    {'b'}
    

Any suggestions on this? It would be of great advantage, as users sometimes have to navigate quite deeply into the database.

Thank you very much for your help,

Anna

Answer 1

[Guillaume]

The reason why tab completion doesn't work for the content of a cell array can easily be explained: matlab does not look into the cell array to see what type of data is stored there.

Now you could argue that maybe it should but maybe it shouldn't. After all, cell arrays are used to store heterogeneous data, so most likely while it may be a structure in there now, maybe it will be a double next time. cell content tend to change type more often than variables do. And if all the cells are always a structure, why aren't you using a structure array instead? Tab completion will work without problems on a structure array.

In any case, the current version of matlab does not look inside the cell array, so there's no work around.

[Guillaume]

Anna's comment posted as an answer moved here:

Thank you very much for your quick answer. Then I'll be hoping for a change in future releases...

I see your point with the structs inside a cell, but unfortunately this does not work for instances of classes when I want to be able of storing a previously unknown number of instances within one data type...

[Guillaume]

By default, class instances are arrays, so you don't need a cell array for that (unless you've coded the class in a way that completely breaks if the instances are not scalar, or you've specifically disallowed array creation).

Even if you want to store polymorphic objects, if they all inherit from the same base class, you can all store them in a plain array, as long as the base class inherits from matlab.mixin.Heterogeneous.

But yes, sometimes you have to use a cell array and you won't get tab completion.

[Anna]

"By default, class instances are arrays, so you don't need a cell array for that (unless you've coded the class in a way that completely breaks if the instances are not scalar, or you've specifically disallowed array creation). "

I didn't know that - just tried it and it works fantastically! Thanks for the hint!

Answer 2

[Ken Atwell]

If you can try the just-released R2019a, MATLAB will now tab completion in this situation.

[Anna]

Oh really? Great!! I'll propably wait until the release of 2019b, but then will definitively upgrade! Thank you very much for this information!