C++: Add "reference_wrapper" declarations to "libcpp.functional" (GH-…

…5671)

Cython/Includes/libcpp/functional.pxd

@@ -19,3 +19,8 @@ cdef extern from "<functional>" namespace "std" nogil:
         # https://github.com/cython/cython/issues/3193
         greater() except +
         bool operator()(const T& lhs, const T& rhs) except +
+
+    cdef cppclass reference_wrapper[T]:
+        reference_wrapper()
+        reference_wrapper(T)
+        T& get() const

tests/run/cpp_stl_cpp11.pyx

@@ -12,6 +12,20 @@ from libcpp.pair cimport pair
 from libcpp.map cimport map
 from libcpp.set cimport set
 from libcpp.deque cimport deque
+from libcpp.functional cimport reference_wrapper
+
+
+def test_reference_wrapper():
+    """
+    >>> test_reference_wrapper()
+    'pass'
+    """
+    cdef:
+        int x = 1
+        vector[reference_wrapper[int]] ref_wrap_vector
+    ref_wrap_vector.push_back(reference_wrapper[int](x))
+    assert ref_wrap_vector[0].get() == 1
+    return "pass"
 
 
 def test_vector_functionality():