Changing sizes of variables by indexing past their size causes a known limitation, which is documented here:
https://www.mathworks.com/help/releases/R2022b/fixedpoint/ug/limitations-with-variable-size-support-for-code-generation.html#bq1h2z9-86
This specific case of indexing using "end + 1" will compile correctly in R2023a when the "Enable variable-sizing" option is set, as described here:
https://www.mathworks.com/help/releases/R2023a/coder/ug/grow-arrays-using-end-plus-one-indexing.html
In general, this issue is only caused when variables are implicitly resized using indexing operations, so the issues can be resolved by either (a) initializing the variable to the largest required size or (b) extending the variable explicitly without using indexing.
For example, the given code could be converted to the following, which compiles correctly:
function v = test_fcn()
coder.varsize("v", [1 2]);
v = zeros(1, 2); % Initialize 'v' at its maximum size, in this case a 1x2 matrix
v = [v 1]; % Was `v(end + 1) = 1`
rand;
end
An alternative solution is to pre-allocate the variables to their maximum size. For example, the given code could be converted to the following:
function v = test_fcn()
coder.varsize("v", [1 2]);
v = zeros(1, 2); % Initialize 'v' at its maximum size, in this case a 1x2 matrix
v(2) = 1;
rand;
end
