TruffleSOM does not accept writes to method arguments

[gpummer]

SOM accepts writes to method arguments. TruffleSOM throws a runtime exception at compile time. Is this the expected behaviour?

I have written the following attached TestCase ArgumentReadonlyTest.som.txt. The runtime exception is found in the attached file
exception.txt.
('mysom' is 'som' with the change from 'som.vm.Universe' to 'trufflesom.vm.Universe'.)

Maybe the root cause has something to do with the setting von JAVA_HOME and GRAAL_HOME? I'm only able to run the provided samples in truffleSOM if JAVA_HOME is identical to GRAAL_HOME and points to the 'normal' Java VM. If GRAAL_HOME points to '... graalvm-ce-1.0.0-rc8/Contents/Home' I get the exception, that 'Caused by: java.lang.AssertionError: Only one implementation Engine.Impl allowed.'.

[smarr]

Hm, this is indeed a departure from SOM.

Though, it is the standard semantics in various Smalltalks, I believe.
So, I would tend to consider it a bug in SOM.

Beside GCBench.som, is there any other reason why writing to arguments would be desirable?

[gpummer]

I have tested this now with Pharo (6.1) which does not allow a write to an argument. I'm really fine with the readonly behaviour.

Just wondering, why this went so long (24 Oct 2013) unnoticed ;) I was surprised, because SOM accepted it. I write most source code in Java - where the write to an argument is fine, so the argument write didn't trigger anything.

[smarr]

Yeah, I don't remember any specific reason of disallowing the writes.
I think, I was just used to it from other Smalltalks, and didn't pay too much attention to SOM when implementing TruffleSOM.

But, I think, it's not a bad idea to stick more strictly to the common Smalltalks.

So, I'll close this issue, and mark it as a bug for SOM to have writable arguments.

Thanks for pointing it out :)
SOM isn't a huge project, and we haven't had a chance recently to expose it to larger number of students. So, such inconsistencies aren't necessarily noticed easily.

Thanks!

[smarr]

Hmm, needs another careful thought as per discussion on SOM-st/SOM#7