[Cython] Type inference and C++

[Stefan Behnel]

Vitja Makarov, 23.07.2012 07:13:
> Here is part of original testcase:
> 
> from cython.operator cimport dereference as d
> from cython.operator cimport preincrement as incr
> from libcpp.vector cimport vector
> 
> def reverse_iteration_test(L):
>     v = new vector[int]()
>     for a in L:
>         v.push_back(a)
>     it = v.rbegin()
>     while it != v.rend():
>         a = d(it)
>         incr(it)
>         print(a)
> 
> It doesn't work with local type inference enabled since `a` in
> for-loop is infered as pyobject and in while loop it's inferred as
> reverse_iterator.
> 
> Then I tried to comment out for loop and compile it with
> upstream/master, same error here:
> 
> note: cpp_stl_vector.pyx:8:6: inferred 'v' to be of type 'vector[int] *'
> note: cpp_stl_vector.pyx:11:7: inferred 'it' to be of type 'reverse_iterator'
> note: cpp_stl_vector.pyx:13:10: inferred 'a' to be of type 'reverse_iterator'
> 
> Error compiling Cython file:
> ------------------------------------------------------------
> ...
>     v = new vector[int]()
>     #for a in L:
>     #    v.push_back(a)
>     it = v.rbegin()
>     while it != v.rend():
>         a = d(it)
>             ^
> ------------------------------------------------------------
> 
> cpp_stl_vector.pyx:13:13: Cannot assign type 'int &' to 'reverse_iterator'
> 
> Error compiling Cython file:
> ------------------------------------------------------------
> ...
>     #    v.push_back(a)
>     it = v.rbegin()
>     while it != v.rend():
>         a = d(it)
>         incr(it)
>         print(a)
>               ^
> ------------------------------------------------------------
> 
> cpp_stl_vector.pyx:15:15: Cannot convert 'reverse_iterator' to Python object
> 
> 
> I think it's not correct to infer `a` as reverse_iterator because it's
> not an iterator it's vector's item.

Right. DereferenceNode should implement infer_type().

Stefan