Does fileDatastore not implement "matlab.io.Datastore"?

I'm currently developing a custom datastore that takes an existing datastore and adds some features.

In the constructor I would like to make sure that a passed argument is of type "matlab.io.Datastore" so I do:

assert(isa(ds, "matlab.io.Datastore"), ...)

This works fine for another custom datastore that directly implements "matlab.io.Datastore" but it does not work when das is created using

ds = fileDatastore(...)

fileDatastore. Form digging around in the source of "matlab.io.datastore.FileDatastore" I found out that it at some point implements "matlab.io.Datastore" but still above is not wokring. Am I missing somehting obvious?

Answer 1

[Shlok]

Hi Eike,

The “matlab.io.datastore.FileDatastore” class does not implement the “matlab.io.Datastore” interface. As a result, “assert(isa(ds, 'matlab.io.Datastore'), ...)” returns “false” when used for “fileDatastore()” instance.

You can verify this by using the “superclasses” function, which lists all the superclasses of a given class.

superclasses(ds)

Output:

From the output above, you can see that “matlab.io.datastore.FileDatastore” implements “matlab.io.datastore.Datastore” instead of “matlab.io.Datastore”. Therefore, you need to modify the code as follows to return “true”:

assert(isa(ds, "matlab.io.datastore.Datastore"), ...); 

To know more about “fileDatastore”, refer to the following documentation link:

https://www.mathworks.com/help/releases/R2020b/matlab/ref/matlab.io.datastore.filedatastore.html