[Cython] Type inference and C++

[Vitja Makarov]

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.

-- 
vitja.