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Match rule returning existing object ? [message #1803680]

Wed, 06 March 2019 16:55

G LG

Messages: 4
Registered: March 2019

Junior Member

Is it possible to write a matching rule that returns an existing object (result of another rule) ?

Suppose I have the following source metamodel:
SrcAbs <|- SrcA
SrcAbs <|- SrcB { elems : SrcAbs* }
SrcAbs <|- SrcC { root : SrcAbs }
...
One abstract class (SrcAbs) and many classes (SrcA, SrcB, ...) inheriting from the abstract class, and some of which contains attributes pointing to one or many elements of the abstract class type.

The target metamodel is similarly structured:
TgtAbs <|- TgtA
TgtAbs <|- TgtB { elems : TgtAbs* }
TgtAbs <|- TgtC { root : TgtAbs }

In the case of the transformation of SrcB, I want to retrun a TgtA if elems is empty, a TgtB if elems has more than 1 elements, and the transformation of elems.first() if elems has exactly 1 element.

rule A {
from f : ...!SrcB ( f.elems.isEmpty() )
to t : ...!TgtA
}
rule B {
from f : ...!SrcB ( f.elems.size() > 1 )
to t : ...!TgtB ( elems <- f.elems )
}

Can I write a matching rule to handle the case f.elems.size() = 1 ?

If not, what is the best way to handle this case if:
- I'm writing a normal module (Src -> Tgt) ?
- I'm writing a refining module (where I want only to replace TgtB with 1 element in elems by this element) ?

Thanks

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Re: Match rule returning existing object ? [message #1804229 is a reply to message #1803680]

Wed, 20 March 2019 19:39

Dennis Wagelaar

Messages: 581
Registered: September 2012
Location: Belgium

Senior Member

If you want to map multiple input elements to the same output element, you can use the Canonic Element pattern.

Cheers,
Dennis

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Re: Match rule returning existing object ? [message #1806531 is a reply to message #1804229]

Fri, 10 May 2019 08:43

G LG

Messages: 4
Registered: March 2019

Junior Member

Hi,

Thank you for your answer. However, I do not see how to use the Canonic Element pattern in my case.

What I want is, for example, the following transformation : "(C : SrcC)-root->( (B : SrcB)-elems->{ (A : SrcA) } )" into "(C' : TgtC)-root->( (A' : TgtA) )" where (O : T)-f->X means object O of type T with field f referencing X.

The semantics of the rule for SrcB with only 1 element in elems would be something like :
rule B {
from f : ...!SrcB ( f.elems.size() = 1 )
to [do not create a new object but use/return the result of the transformation of f.elems.get(0)]
}

Thanks

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Re: Match rule returning existing object ? [message #1806843 is a reply to message #1806531]

Thu, 16 May 2019 07:01

Dennis Wagelaar

Messages: 581
Registered: September 2012
Location: Belgium

Senior Member

If you want to "skip over" certain input elements, perhaps this transformation can provide some inspiration:

https://git.eclipse.org/c/mmt/org.eclipse.atl.git/tree/plugins/org.eclipse.m2m.atl.emftvm.compiler/transformations/InlineCodeblocks.atl?id=2bcbeec856bbd9b2488c17c30ffd34c5449505a0

It flattens nested blocks of instructions, where possible, and thereby "skips over" some input elements. It does differ in that this is a refining mode transformation, however.

Cheers,
Dennis

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