[C++-sig] CEGUI, Python, C++ and signature errors, oh my!

[Max Piepenbrink]

Hey everyone,

I'm working on a pretty straight forward obstacle right now. I'm doing a
game project with CEGUI (http://www.cegui.org.uk/wiki/index.php/Main_Page),
and Boost.Python (compiled as a shared lib against Stackless, actually),
I've successfully learned enough to expose some really useful stuff, I've
written converters and exposures for a few basic types of CEGUI's bread and
butter classes (UVector2, UDim, String) and exposed a whole bunch of primary
functions/properties, but I ran into an issue when setting up a specific
method. I had this issue earlier today, I was getting a signature error, it
ended up fixing itself somehow and I was never able to reproduce it in that
context (version control? what's that?), but I've run into it again and this
time it's not magically fixing itself. I've done a few hours of googling and
come across some resources that were mildly useful in exposing the issue
which I'll leave linked at the bottom. Signature errors at runtime are
common enough, but apparently very "scattered" when it comes to why people
run into it, which is why I'm having such a hard time.

I'm not a seasoned/battle hardened programmer so I hope it doesn't end up
being something really stupid! (hint: it probably will)

So let's jump into it. I'm going to go through my logic for each of my steps
to hopefully expose a possible "misunderstanding" as far as my approach is
concerned.

Here's my C++ which exposes the base Window class (no pure virtuals or
anything, it's fully usable):

class_< CEGUI::Window, boost::noncopyable >("UIWindow",no_init)
.def("__init__", make_constructor(GetWindow))
.def<void (CEGUI::Window::*)(const CEGUI::String&)>("addChildWindow",
&CEGUI::Window::addChildWindow)
.def<void (CEGUI::Window::*)(CEGUI::Window*)>("addChildWindow",
&CEGUI::Window::addChildWindow)

This works beautifully, here you can witness two overloads which both work
exactly how they should.
CEGUI::Window::addChildWindow(const CEGUI::String&)
CEGUI::Window::addChildWindow(CEGUI::Window*)
This works so well that I can use them exactly as I hoped in Python

noodle = UIWindow("Theme/Window","Noodle")
foo = UIWindow("Theme/Window","Foo")
zebra = UIWindow("Theme/Window","Zebra")
noodle.addChildWindow("foo") # adding a child by resolving reference by
String (the 2nd param of the ctor)
foo.addChildWindow(zebra) # adding a child from immediate reference

The fundamental reason this can work is because I have written a converter
for Python's str to CEGUI::String. Which leads me to my next step (and the
problem)

Let's add onto my class exposure, I want to expose two functions,
// CEGUI::Event::Group is a typedef for unsigned int
virtual CEGUI::Event::Connection subscribeScriptedEvent(const CEGUI::String&
name, Event::Group group, const CEGUI::String& subscriber_name);
virtual CEGUI::Event::Connection subscribeScriptedEvent(const CEGUI::String&
name, const CEGUI::String& subscriber_name);

So I write them out (I'm not doing any using; here, since explicit is best
in this case)
.def<CEGUI::Event::Connection(CEGUI::Window::*)(const CEGUI::String&,
CEGUI::Event::Group, const
CEGUI::String&)>("subscribeScriptedEvent",&CEGUI::Window::subscribeScriptedEvent)
.def<CEGUI::Event::Connection(CEGUI::Window::*)(const CEGUI::String&, const
CEGUI::String&)>("subscribeScriptedEvent",&CEGUI::Window::subscribeScriptedEvent)

To be sure that Connection wont cause any big trouble I wrote a dummy
converter (I don't care about it right now, I just want the base
functionality of the subscribeScriptedEvent to work, could this be the
issue? I havent sorted out how I'm going to convert Event::Connection to a
PyObject yet...)

struct CEGUI_Connection_To {
static PyObject* convert(CEGUI::Event::Connection const& s)
{
return NULL;
}
};

I registered the above convert-to, compiled, then I gave it a twirl!

ref_test.subscribeScriptedEvent("OnClicked","call_me")

Traceback (most recent call last):
  File "<string>", line 59, in <module>
Boost.Python.ArgumentError: Python argument types in
    UIWindow.subscribeScriptedEvent(UIWindow, str, str)
did not match C++ signature:
    subscribeScriptedEvent(class CEGUI::Window {lvalue}, class
CEGUI::String, cl
ass CEGUI::String)
    subscribeScriptedEvent(class CEGUI::Window {lvalue}, class
CEGUI::String, un
signed int, class CEGUI::String)

This is strange to me, since I have converters (implicitly and explicitly)
for CEGUI::Window, AND for CEGUI::String, both of which were shown to work
up above in my earlier example. It really seems like
(UIWindow, str, str) should line up with  (class CEGUI::Window {lvalue},
class CEGUI::String, class CEGUI::String) given that I am basically doing
this above just with one less CEGUI::String

My shot-in-the-dark-error-message-googling lead me to some vague
explanations of common reasons for this problem, one of which might apply to
me but I am simply too dim to comprehend:
* http://regina.sourceforge.net/docs/python-caveats.html#python-ownership goes
over some ownership concerns and how this error can sometimes be a result of
ownership issues (I'm not sure that's the problem? I played with some
Callpolicies but assumed the defaults should be fine for this relatively
simple dummy function)
* http://mail.python.org/pipermail/cplusplus-sig/2004-June/007204.html an
older posting from this very mailing list (haha!) but I simply don't
understand his solution.

I basically went through the first ~20 results from
http://www.google.com/search?sourceid=chrome&ie=UTF-8&q=did+not+match+C%2B%2B+signature:+python
and
went back through the docs trying to see what I'm messing up, but I'm
getting kind flustered and figured I'd eloquently ask it here.

It's highly likely I'm butchering Python by not using the right call policy
(I tried a few and just got hideous compile errors unrelated to syntax, put
some thought into it, got scared, ran back to
defaults/return_internal_reference<>() ), or that I'm simply forgetting a
single, important template parameter somewhere. But at this point I feel
like it SHOULD work.

I'm pretty sure I gave enough information to outline the problem/what basic
steps I took to troubleshoot, any help on the matter and illumination on my
poor understanding as to why this is happening is greatly appreciated!

Thanks,
Max Piepenbrink
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