Custom Errors in Modelica

In Modelica, we can create custom error types by extending the Exception class. Here’s an example that demonstrates this concept:

model CustomErrors
  class ArgError
    extends Exception;
    Integer arg;
    String message;
    
    function constructor
      input Integer arg;
      input String message;
      output ArgError error;
    algorithm
      error.arg := arg;
      error.message := message;
    end constructor;
    
    function errorMessage
      input ArgError error;
      output String message;
    algorithm
      message := String(error.arg) + " - " + error.message;
    end errorMessage;
  end ArgError;
  
  function f
    input Integer arg;
    output Integer result;
    output ArgError error;
  algorithm
    if arg == 42 then
      error := ArgError.constructor(arg, "can't work with it");
      result := -1;
    else
      result := arg + 3;
      error := ArgError.constructor(0, "");
    end if;
  end f;
  
  Integer result;
  ArgError error;
equation
  (result, error) = f(42);
  
algorithm
  if error.arg <> 0 then
    Modelica.Utilities.Streams.print(String(error.arg));
    Modelica.Utilities.Streams.print(error.message);
  else
    Modelica.Utilities.Streams.print("No error occurred");
  end if;
end CustomErrors;

In this Modelica example, we’ve created a custom error type called ArgError that extends the Exception class. It has properties for the argument and an error message, similar to the Go example.

The f function demonstrates how to use this custom error type. If the input argument is 42, it returns an ArgError instance along with a result of -1.

In the main part of the model, we call the f function with an argument of 42 and then check if an error occurred. If it did, we print the error details.

To run this Modelica model, you would typically use a Modelica simulation environment. The output would be similar to:

42
can't work with it

Note that Modelica doesn’t have a direct equivalent to Go’s errors.As function. Instead, we’re checking if an error occurred by examining the arg property of our custom error type. In a more complex system, you might implement a more sophisticated error handling mechanism.

Modelica’s approach to error handling is quite different from Go’s, as Modelica is primarily used for modeling and simulation rather than general-purpose programming. However, this example demonstrates how you can implement a similar concept of custom errors in Modelica.