Does Groovy "as" operator create a subclass at run time for User defined classes? - groovy

Question

In Groovy When I write the below code in a groovy script.
class Emp {
public String getId() {
return "12345";
}
}
def coercedInstance = [
getId: {
"99999"
}
] as Emp
println new Emp().getId()
println coercedInstance .getId()
Using the as Operator here, am I creating a sub class of the actual Emp class at runtime and providing the method body at run time?
I have seen other stack overflow articles and i have learnt that Groovy uses DefaultGroovyMethods.java & DefaultTypeTransformation.java to do the coercion. But could not figure out if it was subclassing or not.

Answer 1

Yes, an as operator creates an object which type is a subclass of the target class. Using DefaultGroovyMethods.asType(Map map, Class clazz) generates (in a memory) a proxy class that extends given base class.
class Emp {
public String getId() {
return "12345";
}
}
def coercedInstance = [
getId: {
"99999"
}
] as Emp
assert (coercedInstance instanceof Emp)
assert (coercedInstance.class != Emp)
assert (Emp.isAssignableFrom(coercedInstance.class))
println coercedInstance.dump() // <Emp1_groovyProxy#229c6181 $closures$delegate$map=[getId:coercion$_run_closure1#7bd4937b]>
What happens in your case specifically is the following:
The asType method goes to line 11816 to execute ProxyGenerator.INSTANCE.instantiateAggregateFromBaseClass(map, clazz);
In the next step, ProxyGeneratorAdapter object gets created.
In the last step, adapter.proxy(map,constructorArgs) gets called to return a newly generated class that is a proxy of the base class.