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[acceleo] let =null [message #1756419]

Thu, 16 March 2017 15:47

louis andia.

Messages: 47
Registered: November 2016

Member

Hello,

I have a trouble with acceleo let.
When i have something like [let var: myObject = getMyObject('objectName')] and when "getMyObject" can return null, next instructions in my template are not executed and it's like an exit without any error.
I have to use OclAny to avoid that ( [let var: OclAny= getMyObject('objectName')] .
Is it the good behavior? Am I using acceleo the wrong way? It's look like dangerous to use something else than OclAny as type for a let, if your are not sure at 100% they is any possibility than your right part return null...

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Re: [acceleo] let =null [message #1756427 is a reply to message #1756419]

Thu, 16 March 2017 17:05

Ed Willink

Messages: 7655
Registered: July 2009

Senior Member

Hi

What you observe sounds familiar. https://bugs.eclipse.org/bugs/show_bug.cgi?id=320890

(The more recent Pivot-based OCL supports multiplicities more explicitly so you should be able to declare a let variable as [1] or [?].)

Today, it seems like OclAny gives you a workaround.

Regards

Ed Willink

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Re: [acceleo] let =null [message #1756436 is a reply to message #1756427]

Thu, 16 March 2017 20:27

louis andia.

Messages: 47
Registered: November 2016

Member

Thanks you for your answer.
Yes it's look like they is a similarity between these bugs.

OclAny works but it's not perfect. You have to use oclAsType every time you want to use it, and code is less readable.

If you have any documentation about Pivot-based OCL i take it, but i doubt acceleo let using it.

In fact, you have a warning when you try to affect null value directly, but using just a if statement and it disappear:
1) Warning "Possible incompatible type between 'String' and 'OclVoid'."
[let var: String = null]
[/let]
2) No warning
[let var: String = if true then null else '' endif]
[/let]

[Updated on: Thu, 16 March 2017 20:28]

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Re: [acceleo] let =null [message #1756437 is a reply to message #1756436]

Thu, 16 March 2017 20:46

Ed Willink

Messages: 7655
Registered: July 2009

Senior Member

Hi

The Pivot-based OCL protypes solution to the many problems identified in http://www.omg.org/cgi-bin/doc?ad/14-03-05.pdf

One day it might happen. Then OCL-based specifications might follow suit.

MOFM2T 1.0 has an explicitly inconsistent let. Should it change?

MOFM2T has no active community maintaining the specification, so there is no progress/clarification/fixing wrt MOFM2T 1.0. Acceleo was revised to align with MOFM2T and makes a good attempt at implementing it, however there has been no feedback of Acceleo 'fixes' to create a MOFM2T 1.1.

IMHO M2T actually only requires two facilities not available in M2M languages: a) text output models, b) string template expressions. Better to upgrade OCL with b) and QVT with a). cf Xtend that supports M2T as part of a much more general facility.

Regards

Ed Willink

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Re: [acceleo] let =null [message #1756439 is a reply to message #1756437]

Thu, 16 March 2017 21:32

louis andia.

Messages: 47
Registered: November 2016

Member

Thanks you. I read the MOFM2T definition of let block and i understand the problem better.

I could use others blocks (elselet and else) but in my case it means code duplication instead of using an if block on a specific part.
It should be great to have a special value like "undefined" matching every type, or an option in let to authorize null value, or a finallet block to execute code regardless the value type of the let.

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Re: [acceleo] let =null [message #1756453 is a reply to message #1756439]

Fri, 17 March 2017 07:18

Ed Willink

Messages: 7655
Registered: July 2009

Senior Member

Hi

Yes, all suggestions worth considering.

You could raise an issue with the MOFM2T specification, but since no Revision Task Force has been chartered in the nine years since the standard was produced, it is clear that there is a very low level of interest in MOFM2T amongst OMG member companies or serious enthusiasts. Obeo, the developers of Acceleo, choose not to be an OMG member.

You could raise a Bugzilla against Acceleo, but as indicated in Bug 320890, MOFM2T compatibility inhibits most solutions.

Regards

Ed Willink

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