Why do I receive a warning about a value indexed with no subscripts?

Why do I receive the warning below that says a value was indexed with no subscripts, and this will be an error in a future release? 

Warning: A value of class "<some class>" was indexed with no subscripts
specified. Currently the result of this operation is the indexed value
itself, but in a future release, it will be an error.

Answer 1

[MathWorks Support Team]

Starting with MATLAB R2023a, the behavior of indexing with no subscripts remains the same and does not error, but the warning no longer appears. Using the warning command to turn the warning on or off has no effect. For more information, see the linked MATLAB release note:

https://www.mathworks.com/help/matlab/release-notes.html?category=language-programming&rntext=subscript&startrelease=R2023a&endrelease=R2023a&groupby=release&sortby=descending&searchHighlight=subscript#mw_6f66532c-0239-4787-a52a-7521affd6e6a

The source of a warning with the structure is code that uses indexing into variables with empty parentheses. This warning message is 'off' by default. In MATLAB R2017b, you can reproduce this warning by turning the warning on and indexing into an array without a subscript.

>> a = zeros(1, 3);
>> warning("on", "MATLAB:subscripting:noSubscriptsSpecified")
>> a()
Warning: A value of class "double" was indexed with no subscripts specified. Currently the result of this operation is the indexed value itself, but in a future release, it will
be an error. 

ans =

     0     0     0

If you are using MATLAB R2022b or earlier releases, you can turn off this warning. Execute this command in MATLAB to turn off the warning:

>> warning("off","MATLAB:subscripting:noSubscriptsSpecified");

[Nicholas Ayres]

I'm working within the app editor and keep receiving this warning when I'm pressing buttons within the editor.

I assume the code that runs the editor must be the thing triggering this warning? as my code does not use the above. Hopefully the whole editor does not break in a future release!

Answer 2

[James Lebak]

This warning was removed in R2023a. More details are in the release notes.