Xbase's new JvmUnknownTypeReference

#19 Xbase's new JvmUnknownTypeReference

Jul 09, 2013 | 7 minutes | Beginners, Xbase
New nice little feature of the Xtext 2.4 is the use of JvmUnknownTypeReference instead of the 'null' to represent references to missing types. In this episode, you will see the differences between Xtext 2.3 and Xtext 2.4 in creation and use of type references.
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Differences between Xtext 2.3 and Xtext 2.4

The class references can be created using JvmTypesBuilder.newTypeRef(...) extension method. In following snippet we will use references to following missing types:

  • test.MyEntity1Interface or entity.fullyQualifiedName + "Interface"
  • test.MyEntity1Factory or entity.fullyQualifiedName + "Factory"

Implementing interface, that doesn't exist

DomainmodelJvmModelInferrer.xtend 
...
acceptor.accept(entity.toClass(entity.fullyQualifiedName)).initializeLater [
  ...
  // ADDED
  superTypes += entity.newTypeRef(entity.fullyQualifiedName + "Interface")
  ...
]

 

  • Xtext 2.3 implements no interface:
src-gen/test/MyEntity1.java 
public class MyEntity1 {
  ...
}

 

  • Xtext 2.4 implements missing interface producing java compilation error:
src-gen/test/MyEntity1.java 
public class MyEntity1 implements test.MyEntity1Interface {
  ...
}

Defining field of type, that doesn't exist

DomainmodelJvmModelInferrer.xtend 
...
acceptor.accept(entity.toClass(entity.fullyQualifiedName)).initializeLater [
  ...
  // ADDED
  members += entity.toField("factory", newTypeRef(entity.fullyQualifiedName + "Factory"))
  ...
]

 

  • Xtext 2.3 defines a field of type Object and a comment with a warning:
src-gen/test/MyEntity1.java 
public class MyEntity1 {
  private Object /* problem during compilation, see error log*/ factory;
  ...
}
...

 

  • Xtext 2.4 defines a field of missing type producing java compilation error:
src-gen/test/MyEntity1.java 
public class MyEntity1 implements test.MyEntity1Interface {
  private test.MyEntity1Factory factory;
  ...
}

Appending types in the body = [ ... ] parts

  • In Xtext 2.3 you have to do a 'null' check after creating a new type reference:
DomainmodelJvmModelInferrer.xtend 
body = [
  ...                                        
  // ADDED
  val factoryTypeRef = entity.newTypeRef(entity.fullyQualifiedName + "Factory")
  if (factoryTypeRef != null) {
    newLine
    it.append(factoryTypeRef.type)
    it.append(" factory = null;")
  }
  ...
]

In case entity.fullyQualifiedName + "Factory" not found, no local variable get defined.

  • In Xtext 2.4 you can easily implement your own append(ref) method to reference missing types:
DomainmodelJvmModelInferrer.xtend 
  body = [
    ...
    // ADDED
    newLine
    val ref = entity.newTypeRef(entity.fullyQualifiedName + "Factory")
    append(ref)
    append(" a;")
  ]

...

def append(IAppendable it, JvmTypeReference typeRef) {
  if (typeRef instanceof JvmUnknownTypeReference) {
    append(typeRef.getQualifiedName('.'))
  } else {
    append(typeRef.type)
  }
}

 

In case test.MyEntity1Factory not found, the local variable still get defined:

src-gen/test/MyEntity1.java 
...

public MyEntity1(final Procedure1<MyEntity1> initializer) {
  initializer.apply(this);
  test.MyEntity1Factory a;
}
...