Fix issue with const reference returned results.

This is a bit of a hack, but as Cython doesn't yet understand
const overloads with different (usually const) return types,
it can't provide the right type of reference in this case.

Cython/Utility/ModuleSetupCode.c

@@ -250,7 +250,9 @@ template<typename T>
 class __Pyx_FakeReference {
   public:
     __Pyx_FakeReference() : ptr(NULL) { }
-    __Pyx_FakeReference(T& ref) : ptr(&ref) { }
+    // __Pyx_FakeReference(T& ref) : ptr(&ref) { }
+    // Const version needed as Cython doesn't know about const overloads (e.g. for stl containers).
+    __Pyx_FakeReference(const T& ref) : ptr(const_cast<T*>(&ref)) { }
     T *operator->() { return ptr; }
     operator T&() { return *ptr; }
   private:

tests/run/cpp_template_ref_args.h

@@ -5,6 +5,7 @@ template <typename T>
 struct Bar {
     Bar & ref() { return *this; }
     const Bar & const_ref() { return *this; }
+    const Bar & const_ref_const() const { return *this; }
     T value;
 };
 

tests/run/cpp_template_ref_args.pyx

 # tag: cpp
 
+from libcpp.vector cimport vector
+
 
 cdef extern from "cpp_template_ref_args.h":
 
@@ -9,6 +11,7 @@ cdef extern from "cpp_template_ref_args.h":
         T value
         Bar[T] & ref() except +
         const Bar[T] & const_ref() except +
+        const Bar[T] & const_ref_const() except +
 
     cdef cppclass Foo[T]:
         Foo()
@@ -39,3 +42,14 @@ def test_template_ref_attr(int x):
     cdef Bar[int] bar
     bar.value = x
     return bar.ref().value, bar.const_ref().value
+
+def test_template_ref_const_attr(int x):
+    """
+    >>> test_template_ref_const_attr(4)
+    4
+    """
+    cdef vector[int] v
+    v.push_back(x)
+    cdef const vector[int] *configs = &v
+    cdef int value = configs.at(0)
+    return value