[Cython] Cannot assign type 'set<size_t> &' to 'set<size_t>'

[Dimitri Tcaciuc]

Hello everyone,

Here's a small test case I'm trying to compile. I'm trying to pass a
STL set reference to a method in a template class.

x.pyx:

    from libcpp.set cimport set as cpp_set

    cdef extern from "x.hh":

        cdef cppclass Foo [T]:
            Foo()
            void set_x(cpp_set[size_t] & x)

    cpdef func():
        cdef Foo[int] foo

        cdef cpp_set[size_t] x
        cdef cpp_set[size_t] & xref = x

        foo.set_x(xref)

x.hh:

    #include <set>

    template <typename T>
    struct Foo {
        void set_x(const std::set<size_t> & x) { /* do nothing */ }
    };

To compile,

    bash $ cython --cplus x.pyx

Which results in

    foo.set_x(xref)
                 ^
------------------------------------------------------------
x.pyx:15:18: Cannot assign type 'set<size_t> &' to 'set<size_t>'


However, if I remove the template parameter from Foo, everything works.


y.pyx:

    from libcpp.set cimport set as cpp_set

    cdef extern from "y.hh":

        cdef cppclass Foo:
            Foo()
            void set_x(cpp_set[size_t] & x)

    cpdef func():
        cdef Foo foo

        cdef cpp_set[size_t] x
        cdef cpp_set[size_t] & xref = x

        foo.set_x(xref)

y.hh:

    #include <set>

    struct Foo {
        void set_x(const std::set<size_t> & x) { /* do nothing */ }
    };


>From what I can tell, the CppClassType instance the CReferenceType is
pointing to has the correct name "set<size_t>", however it's a
different class instance. The particular failing expression is in
`ExprNode.coerce_to`

    if not (str(src.type) == str(dst_type) or
dst_type.assignable_from(src_type))


I wish I could suggest a patch, but unfortunately I'm a complete
newbie to Cython internals. Perhaps someone could give a few pointers
as to what should be done to fix this?

Thanks,


Dimitri