Custom Exceptions are broken or mis-documented (Monkey C, SDK and/or documentation bug)

> Many of the examples omit necessary using statements. They typically assume that the reader is familiar enough with the language to know they are necessary.

Okay.

> That code sample does not generate that warning; nothing uses the name UnknownTypeException.

My bad. I copy&pasted the wrong message ^^
The message was of course: `Class 'AppSpecificException' does not initialize its super class, 'Exception'`

I updated the initial post. This is resolved though, because of the typo in the documentation.

Thanks for pointing that out. Sometimes you are too blind to see stuff like that after hours xD

> 4. Compiler goes rouge if custom exception does not have an initializer

> I'd like to see a test case. I know that if you fail to initialize the base class properly you can encounter a system error, but I'd like to see what you're talking about.

I attached a zip with an example. Notice how the stack trace show `source\Test\ClassThatIsNotUsedAnywhere.mc:3` as the source for the exception.

This is mainly a confusing bug for the developers themselves.RougeException.zip

> You can implement an exception factory. I'm not certain why you'd want to do such a thing, but you most definitely can do it.

Could you give me a hint on how to that?

The following does not work:

using Toybox.Lang;

class UnknownTypeException extends Lang.Exception {

    public function initialize(msg) {
        Lang.Exception.initialize();


        self.mMessage = msg;
    }

    public static function create() {
    	return new self("foo");
    }
}

Calling

throw UnknownTypeException.create();

Triggers this during automatic build:

BUILD: ERROR: App.mc:23,36:  missing ';' at '('
BUILD: ERROR: App.mc:23,37:  mismatched input ')' expecting {'{', '(', '[', ':', '+', '-', '~', '!', 'new', 'true', 'false', 'null', 'NaN', '$', IntNumber, HexNumber, OctalNumber, FloatNumber, Id, String, Char}

and calling this:

var e = UnknownTypeException.create();
throw e;

Triggers no error during automatic build, but causes this during the app run:

Error: Unhandled Exception
Exception: UnexpectedTypeException: Expected Class definition, given Object
Stack: 
  - create() at UnknownTypeException.mc:13
  ...

During writing this down, I found that the above code for the factory does not work, because I have used `self` instead of `UnknownTypeException` for the instantiation.

So this would be the correct code:

using Toybox.Lang;

class UnknownTypeException extends Lang.Exception {

    public function initialize(msg) {
        Lang.Exception.initialize();


        self.mMessage = msg;
    }

    public static function create() {
    	return new UnknownTypeException("foo");
    }
}

This code works. (Yeah :D)

I can life with the workaround of putting the exception in a variable before throwing it.

I'm pretty sure Travis has posted code in the past the does the checking with instanceOf to determine the object type.  You could just do something with an enum to return the type and not mess with exceptions, and have a "TypeUnknown" enum if you all through all the if() {} else if() {} conditions.

I use instanceOf in a number of thing, but there it's to insure a type, or possibly follow a different code path based on the type.

"If I see data is an InstanceOf Number in onBackgroundData, it's an error code, else it's real data"

> I've been scratching my head all day trying to figure out what you want to do, and finally found the base code for what you are trying in the programmer's guide.  This is likely really old and updated).

This is why I posted the link for the documentation I was referring to :D

I wanted to give as much context as possible.

If by "API Guide" you mean this site: https://developer.garmin.com/connect-iq/api-docs/Toybox/Lang/Exception.html

and by

> Notice the examples are blank.

There is no actual javascript to toggle the code examples, then I am with you. I am having them both (Programmers guide and API Docs) open all the time.

The problem with the hidden examples on the API docs page above is, that the `<code>` has a class `source_code` which has `display: none` by default.

I am using the API docs that came with the SDK 3.2.2-2020-08-28 for Windows right now, because the bug is already fixed there (no toggles, just showing the examples).

As for

> What is it you want to do?

I am potentially writing a Barrel, to determine the native type of a value (string, number etc.). As far as I saw there is a construct for `instanceof`, but not something like `typeof`(JS).
For that I want to have an exception if the type can not be determined.
The exception can be handle by the app developer who uses the Barrel so there is no crash or something.

Please point me in the right direction, if I have missed something that might already exist.

If you have further questions, please, let me know :)

The typographical error has been fixed, but it won't be published until the next time we push documentation.

> 1. It misses the import for `Toybox.Lang`, so it does not work properly out of the box. Please fix.

Many of the examples omit necessary using statements. They typically assume that the reader is familiar enough with the language to know they are necessary.

> 2. It triggers a build warning: `Unable to detect scope 'UnknownTypesException' for the symbol 'initialize'.`

That code sample does not generate that warning; nothing uses the name UnknownTypeException.

> 3. When the exception is used with a message (`throw new AppSpecificException("foo");`) it triggers this error:

Yes, that is because there is a typographical error. In the code you copy/pasted, the function name is initalize, but it should be initialize.

> 4. If you just deleted the body of the custom exception in hope of the parent have the correct default behavior, the code goes completely rouge

I don't understand what you're doing, so I can't comment.

> Also hard-coded user path in error messages? I'll talk to that rayburn guy ;)

Full paths to source files are built into the debug information when the API is compiled. They could be stripped out.

> Also if you call `new Toybox.Lang.UnexpectedTypeException("ss")`, so with too less arguments, the same error is triggered, although there are not **too many**, but **less than needed** arguments given

If you call new Toybox.Lang.UnexpectedTypeException("ss") you will get Error: Not Enough Arguments Error. This is entirely correct and expected. The documentation for UnexpectedTypeException says that the initialize method takes 3 parameters, and you are passing only 1.

> 1. Please update the documentation

I'll fix the typographical error that I mentioned in my response to #3 above.

> 2. SDK does not trigger wrong warnings for parents of exception not being initialized

Yes, it absolutely does.

using Toybox.Application;
using Toybox.WatchUi;
using Toybox.Lang;
using Toybox.System;

class AppSpecificException extends Lang.Exception {
    function initialize(msg) {
        //Exception.initialize();
        mMessage = msg;
    }
}

class MyUnepxectedTypeException extends Lang.UnexpectedTypeException {
	function initialize(msg) {
		//UnexpectedTypeException.initialize(msg, null, null);
	}
}

.. produces this output when compiled with warnings enabled:

BUILD: WARNING: marqadventurer: /eclipse-workspace/Exceptions/source/ExceptionsApp.mc:7: \
  Class 'AppSpecificException' does not initialize its super class, 'Exception'
BUILD: WARNING: marqadventurer: /eclipse-workspace/Exceptions/source/ExceptionsApp.mc:14: \
  Class 'MyUnepxectedTypeException' does not initialize its super class, 'UnexpectedTypeException'

> 3. Custom Exceptions can not have messages

Yes, they most certainly can. Just be sure to properly spell the word initialize and you'll be fine.

> 4. Compiler goes rouge if custom exception does not have an initializer

I'd like to see a test case. I know that if you fail to initialize the base class properly you can encounter a system error, but I'd like to see what you're talking about.

> 5. Please make exception factories a thing :)

You can implement an exception factory. I'm not certain why you'd want to do such a thing, but you most definitely can do it.