Stop Implicit Type Conversion in Coder

Hello All

As per ISO 26262, for ASIL B to ASIL D, there must not be an implicit data type conversion. But in MATLAB, we can have

testValue = uint8(2);
testValue = -126; % It is perfectly fine but shall throw a warning or error

Is there anyway to throw a compile time warning here? Suggestions are welcome.

Answer 1

[Thomas Blazek]

So, MATLAB is dynamically typed. That means, by assignment, you overwrite the type. It is not a type conversion, it is literally setting a new type. And, MATLAB is very liberal about it. Furthermore, it is interpreted, not compiled, therefore no compile-time checks are possible.

That said, there is a workaround if you really want to be sure. You can Define the following Class

classdef Uint8Class
   properties
      value = []
   end
   methods
      function obj = set.value(obj,in)
         if in >= 0 && in < 256
            obj.value = in;
         else
            error('Not a Uint8')
         end
      end
      function out = get.value(obj)
         out = uint8(obj.value);
      end
   end
end
x = Uint8Class;
x.value = 3; % works
display(x.value)
x.value = -2 % Raises an error

The way this works is that it overrides get and set methods of "x". Then, you can write your own checks on assignment. The downside is that you have to address the value by "variable.value" instead of just "variable", but it does allow for checks as you want them, and even "fails in a meaningful way".

[Abhishek Kumar]

I understand that MATLAB is a dynamically typed language but he question here is regarding a standard which MATLAB Supports (ISO 26262). So if we use MATLAB/Simulink Check, is it possible to get an Error without changing the Class Definition. I would not want to create a DataType Class anyway. Your workaround is quite smart though.

[Thomas Blazek]

Ah ok, sorry I didn't quite catch that, in that case I do not have an idea, Sorry.