[Cython] cython crash: default parameters in methods of template cppclass

[Robert Bradshaw]

On Tue, Mar 22, 2011 at 7:21 AM, Simon Anders <anders at embl.de> wrote:
> Hi,
>
> I found a little bug in Cython 0.14.1.
>
> The following causes the Cython compiler to throw an exception:
>
> ---8<---
> cdef extern from "foo.h":
>   cdef cppclass foo[ T ]:
>      bar( int b = 0 )
>
> cdef foo[ int ] a
> a.bar( 1 )
> ---8<---
>
> The exception is "AttributeError: 'CFuncType' object has no attribute
> 'op_arg_struct'", thrown in line 3044, in generate_result_code. Full stack
> trace attached.
>
> The file compiles without crash if one either
>  - removes the last line, i.e. the call to the class's method, or
>  - removes the template argument, i.e., the "[ T ]" in line 2 and
>      the "[ int ]" in line 5.
>
> Hence, the issue only appears when calling methods of _templated_ classes,
> which have a _default_ value for their argument.

Default arguments in C++ are completely different from default
arguments in Cython, this is our bug for not catching that. You have
to declare this as an overloaded method

cdef extern from "foo.h":
    cdef cppclass foo[ T ]:
       bar()
       bar(int)

Btw, unless it returns an object, you probably want to declare the
return type of your methods. Perhaps we should make this a warning for
extern declarations?

- Robert