In the context of code generation, a variable's datatype cannot be changed once it is assigned to a value. In the function you provided,
s = [];
creates an empty variable with the default data type of “double” in MATLAB. You can check its data type by running:
class(s)
in MATLAB Command Window.
From the perspective of MATLAB Coder, you tried to change the type of "s" from "double" to "struct". While in MATLAB, you can assign a variable with a value of different data type, it generally causes issues during code generation.
A workaround for this issue is to remove the first assignment to "s", so that it is never a "double" to begin with. The function becomes
function out = fnName()
s.x = 10;
end
Now, MATLAB Coder knows that "s" is intended to be a struct with field "x".
