Unexpected behavior of cast method

[gswifort]

The cast() method returns the requested object, even if that object has a type that does not fit into this class. Is this the correct behavior?

>>> ent_id = entsel()
>>> obj = Db.DbObject(ent_id)
>>> obj.isA().dxfName()
'TEXT'

>>> Db.Polyline(ent_id)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
PyDb.ErrorStatusException: Exception!(eNotThatKindOfClass), function openAcDbObject, Line 70, File PyDbObjectId.h:

>>> ent = Db.Entity(ent_id)
>>> Db.Polyline.cast(ent)
<PyDb.Polyline object at 0x0000013250347040>

[CEXT-Dan]

That was my intent, if fact the fist versions didn’t have a cast. I thought it was part of the ugliness of AutoCAD’s .NET interface.
It’s also very slow as it has to walk the class hierarchy. It was even an issue for Autodesk, so they added the class type to the object id.
I had to add cast back in for overrules and events, though best practice is to check the type in the id before you open it, its much faster

        db = Db.curDb()

        texts = []
        
        #if its not a text, we don't even open it
        for id in db.objectIds():
            if id.isDerivedFrom(Db.Text.desc()):
                texts.append(Db.Text(id))

the no check allows overrules to perform quite well

[CEXT-Dan]

more reading
AcRxObject::cast(), and this will be substantially slower (some tests indicate a factor of 5)
https://adndevblog.typepad.com/autocad/2012/12/issues-regarding-runtime-type-identification-and-casting-in-c.html

edit : I suppose that's pretty import to have documented

[CEXT-Dan]

I could add a safeCast method if you think we need one

[gswifort]

I think it's unnecessary, isDerivedFrom is enough