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[SOLVED] Grammar Warning The rule ... may be consumed without object instantiation. [message #846089]

Sun, 15 April 2012 15:00

kon f
Messages: 28
Registered: March 2012

Junior Member

Hey Guys!

I'm reading the Xtext documentation and was playing around with some examples. I found a nice one that uses unordered groups to explain the modifiers of the Java language:

enum Visibility:
	PUBLIC='public' | PRIVATE='private' | PROTECTED='protected';

Modifier:
	(static?='static')? & (final?='final')? & visibility=Visibility;

Since the Java language also provides the none (or package) modifier, I extended the example (wrapped the visibility assignment with optional cardinality):

enum Visibility:
	PUBLIC='public' | PRIVATE='private' | PROTECTED='protected';

Modifier:
	(static?='static')? & (final?='final')? & (visibility=Visibility)?;

Now, I'm getting a warning: The rule 'Modifier' may be consumed without object instantiation. Add an action to ensure object creation, e.g. '{Modifier}'.

I found some similar issues on this website and understand the reason for the warning, but I wasn't able to get rid of it.

I don't know if my approach is straightforward. Thank you Smile

Kon

[Updated on: Sun, 15 April 2012 16:45]

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Re: Grammar Warning The rule ... may be consumed without object instantiation. [message #846104 is a reply to message #846089]

Sun, 15 April 2012 15:22

Christian Dietrich
Messages: 4412
Registered: July 2009

Senior Member

Modifier:
{Modifier} ((static?='static')? & (final?='final')? & (visibility=Visibility)?);

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Re: Grammar Warning The rule ... may be consumed without object instantiation. [message #846162 is a reply to message #846104]

Sun, 15 April 2012 16:44

kon f
Messages: 28
Registered: March 2012

Junior Member

Thank you Christian! That example worked.

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Re: Grammar Warning The rule ... may be consumed without object instantiation. [message #852807 is a reply to message #846162]

Sun, 22 April 2012 06:37

kon f
Messages: 28
Registered: March 2012

Junior Member

I just noticed that even with the cardinality set to ? for Visibility, still one instance is created at runtime. Since an enum is required to have one of its declared values, it is set to public (apparently the first one). The following input is correct for my language:

final static int SPEEDLIMIT = 30;

I actually thought, that my Modifier instance is going to look as followed (static and final are primitive values, so they always going to have a default value):

static=true
final=true
visibility=NULL

I'm using NULL value as indicator for package modifier. Am I doing something wrong? Sad

I tried the following and it works as expected:

Test:
'public' | 'private' | 'protected'
;

ModifierField:
{ModifierField}((static?='static')? & (final?='final')? & (visibility=Test)?);

Any suggestions Smile

?

Thank you!

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Re: Grammar Warning The rule ... may be consumed without object instantiation. [message #852817 is a reply to message #852807]

Sun, 22 April 2012 06:52

Christian Dietrich
Messages: 4412
Registered: July 2009

Senior Member

Hi,

the only Possibility i know is to switch to a manually maintained metamodel

~Christian

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Re: Grammar Warning The rule ... may be consumed without object instantiation. [message #852827 is a reply to message #852817]

Sun, 22 April 2012 07:06

kon f
Messages: 28
Registered: March 2012

Junior Member

Thank you Christian! Than I guess, I'll stick with my "Test" solution Wink

By the way, is this behaviour actually intended?

[Updated on: Sun, 22 April 2012 07:09]

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Re: Grammar Warning The rule ... may be consumed without object instantiation. [message #852834 is a reply to message #852827]

Sun, 22 April 2012 07:14

Christian Dietrich
Messages: 4412
Registered: July 2009

Senior Member

i guess yes. it is explained in the docs
http://www.eclipse.org/Xtext/documentation/2_1_0/020-grammar-language.php#syntax_8

Quote:

Please note, that Ecore does not support unset values for enums.

[Updated on: Sun, 22 April 2012 07:16]

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Re: Grammar Warning The rule ... may be consumed without object instantiation. [message #853715 is a reply to message #852834]

Mon, 23 April 2012 05:11

Mikael Karpberg
Messages: 8
Registered: April 2012
Location: Sweden

Junior Member

Seems like the simplest solution is to have something like this, no?

enum Visibility:
	DEFAULT_VIS='__packetvisibilitydefault' | PUBLIC='public' | PRIVATE='private' | PROTECTED='protected';

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Re: Grammar Warning The rule ... may be consumed without object instantiation. [message #854133 is a reply to message #853715]

Mon, 23 April 2012 13:45

Christian Dietrich
Messages: 4412
Registered: July 2009

Senior Member

yes

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Re: Grammar Warning The rule ... may be consumed without object instantiation. [message #856485 is a reply to message #854133]

Wed, 25 April 2012 14:02

kon f
Messages: 28
Registered: March 2012

Junior Member

Apparently, this adds an additional keyword that can be used by the user e.g.

final static __packetvisibilitydefault int SPEEDLIMIT = 30;
final static int SPEEDLIMIT = 30;

Both expressions are valid and have the same meaning. Since code competition suggests __packetvisibilitydefault as possible keyword, I'll keep using:

Visibility:
'public' | 'private' | 'protected'
;

Thanks!

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Re: Grammar Warning The rule ... may be consumed without object instantiation. [message #856559 is a reply to message #856485]

Wed, 25 April 2012 15:38

Christian Dietrich
Messages: 4412
Registered: July 2009

Senior Member

hi as said before. Maintain the meta model manually. Alternatively
overwrite completeKeyword. In the proposal provider and suppress the
super call if the keyword is the __xxxx one

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Re: [SOLVED] Grammar Warning The rule ... may be consumed without object instantiation. [message #857047 is a reply to message #846089]

Thu, 26 April 2012 03:44

kon f
Messages: 28
Registered: March 2012

Junior Member

Hey Christian,

thanks for the information, I didn't think that far - I'm new to Xtext Smile

Kon

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