What do the empty square brackets [] do in the expression executed by eval?

sys = eval([model '(0,[],[],''compile'')']);

[Stephen23]

This question is a reference to:

https://www.mathworks.com/matlabcentral/answers/340030-how-can-i-programmatically-call-examplemodel-compile-using-a-variable-for-my-model-name

Answer 1

[Stephen23]

"What do the empty square brackets [] do in the expression executed by eval?"

Nothing really.

MATLAB has positional input arguments. Many MATLAB functions use an empty numeric array (i.e. []) to indicate that an input argument is undefined, which allows further input arguments to be specified. In your example the 2nd and 3rd arguments are undefined, whilst the 1st and 4th arguments have defined values (i.e. 0 and the char vector 'compile' respectively).

That is all.

Read the function/model documentation to know if [] is accepted as an undefined positional input argument.

This has nothing to do with eval.

Answer 2

[Guillaume]

The same as they always do, concatenate whatever is inside the bracket. model must contain a char vector, so it just appends (0, [], [], 'compile') to whatever is in model.

A much better way of doing the same:

sys = feval(model, 0, [], [], 'compile');

don't use eval!

edit: completely misread the question. As Stephen explains, the brackets inside the call are used to tell the function called by eval to use the default value for that particular input.