Question

I refactored some code, and now I get this error when calling a function. But everything seems to be fine, I even compared failing_argument.GetType().AssemblyQualifiedName between the old and the new code and they are the same. Any ideas what could be wrong?

The invocation of the function is in IronPython code, the function is in C# code (an assembly which didn’t change during this refactoring).

What sort of thing could generate this error?

EDIT: full IronPython traceback:

Traceback (most recent call last):
  File "D:\Work\Framework\python\ide\tab_manager.py", line 57, in add_chart_tab
    chart_tab = ChartTab(self.__main_window, self, tab_item, name, chart_descriptor)
  File "D:\Work\Framework\python\ide\chart_tab.py", line 64, in __init__
    self.__chart = Chart(self, self.__gui_cfg, self.__base_cfg, self.__chart_descriptor, self.__scroll_bar)
  File "D:\Work\Framework\python\ide\chart.py", line 57, in __init__
    self.update_topology(empty=False)
  File "D:\Work\Framework\python\ide\chart.py", line 93, in update_topology
    self.update_config()
  File "D:\Work\Framework\python\ide\chart.py", line 111, in update_config
    self.__global.chart_view = ChartView(self.__global)
  File "D:\Work\Framework\python\ide\chart_view.py", line 33, in __init__
    self.__spans = SpanUtil.compute_spans(time_series, gap_threshold)
TypeError: expected List[DataPoint], got List[DataPoint]

Answer 1

After further debugging I managed to get a different error message from the code: Unable to cast object of type 'List[DataPoint]' to 'List[DataPoint]'

Searching for this yielded a couple of articles explaining the problem:
http://www.infinitec.de/post/2008/05/InvalidCastException-Unable-to-cast-object-of-Type-X-to-X.aspx
http://geekswithblogs.net/rupreet/archive/2010/02/16/137988.aspx

It turns out that the assembly containing DataPoint (from List[DataPoint]) it’s loaded twice in my application from two different locations. The cause in my case is that when Visual Studio builds an assembly, it also copies all the other referenced assemblies next to the newly built one in the bin folder. But I also dynamically load one of the referenced assemblies from it’s original build location.