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Define grammar in Xtext for optional array dimensions [message #1786413]

Thu, 03 May 2018 03:27

Ayman Elkfrawy

Messages: 2
Registered: April 2018

Junior Member

I'm trying to define grammar in xtext for arrays where dimensions can be empty like int[][] or int[5][10]

My grammar looks like:

ArrayType: 
     [BasicType] ('['(dimension+=Expression)?']')+;

The problem with that rule when I use int[][] is there is no way from the model to know how many [] included because dimension list would be empty.

So I wonder if there is a way in xtext to default value like 0 in case Expression wasn't found? Otherwise what is the best way to handle such situation.

Thanks in advance for your help.

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Re: Define grammar in Xtext for optional array dimensions [message #1786512 is a reply to message #1786413]

Fri, 04 May 2018 20:23

Christian Dietrich

Messages: 12237
Registered: July 2009

Senior Member

What about moving these to a subobject

ArrayThingy: component=[Sometype] dimensions += Dimension+;

Dimension: {Dimension}'[' exp=Expression? ']'^

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Re: Define grammar in Xtext for optional array dimensions [message #1786530 is a reply to message #1786512]

Sun, 06 May 2018 00:41

Ayman Elkfrawy

Messages: 2
Registered: April 2018

Junior Member

Thanks Christian,

I thought about this, but I didn't want to change my metamodel. I hoped to find some other solution, but it seems I will need to go with that one.

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Re: Define grammar in Xtext for optional array dimensions [message #1786531 is a reply to message #1786530]

Sun, 06 May 2018 06:46

Christian Dietrich

Messages: 12237
Registered: July 2009

Senior Member

You can always use node model but that sucks usability wise in that usecase

Need professional support for Xtext, Xpand, EMF?
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Blog : https://www.dietrich-it.de

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Re: Define grammar in Xtext for optional array dimensions [message #1786533 is a reply to message #1786531]

Sun, 06 May 2018 07:45

Ed Willink

Messages: 6042
Registered: July 2009

Senior Member

Hi

Changing the metamodel can be a pain, but eventually not changing the metamodel can be a greater pain. Since "[]" is significant, you might care to step back a bit and realize that the indequate distinction between "[]" and "" is actually a metamodel bug that Xtext has identified for you.

Regards

Ed Willink

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