Tuning ELists

Just solved a serious performance problem. I programmtically constructed a rather big EMF model. It took ages so I started a profiler: Most of the time was spend in the BasicEList.contains(EObject) method. 

This is due to the fact that the corresponding EReferences have the unique flag set to true. EMF makes sure each element appears only once in the list of that reference. This is good, but performs poor for big growing lists.

As I construct the model from scratch I can make sure there will be no duplicates. So instead of

parent.getFeature().add(child);

I cast to BasicEList and call

((BasicEList<EObject>) parent.getFeature()).addUnique(child);

In my case, that reduced the execution time to a fifth !

Testing Trees

Working on parsers a lot recently, I have to write quite a bunch of tedious unit tests. Each of these tests analyses an EMF AST model which is the output of the parser. It checks if all nodes are at the right location and if all properties are set correctly. The tests look awful and debugging is a nightmare.

Using Xtext, it is quite easy to create a DSL for tree comparison. I can now describe expected tree results as

Extension {
name=Identifier(value='foo')
params=[
DeclaredParameter {
name=Identifier(value='this')
type=Identifier(value='Object')
},
DeclaredParameter {
name=Identifier(value='that')
type=Identifier(value='Object')
}]
}

where Extension, Identifier and DeclaredParameter are EClasses, name,params and type are EReferences and value is a attribute.

Writing such a DSL and an interpreter doesn't take you a day and will save you a lot of time and mental sanity in the future.