gistfile1.pyx

# case 1
cdef: 
    ffi_type *f_type
    ffi_type* elements[3]

if (some condition......):
    some code........
else:
    # THIS WORKS #
    f_type.size = 0
    f_type.alignment = 0
    f_type.type = FFI_TYPE_STRUCT
    f_type.elements = elements
    elements[0] = &ffi_type_uint64
    elements[1] = &ffi_type_uint64
    elements[2] = NULL

    self.f_result_type = &f_type

#########################################################

# case 2
cdef void _resolve_complex_ffi_type(self):
    cdef: 
        ffi_type *f_type
        ffi_type* elements[3]

    self.f_result_type = <ffi_type*>malloc(sizeof(ffi_type))
    f_type = <ffi_type*>malloc(sizeof(ffi_type))

    f_type.size = 0
    f_type.alignment = 0
    f_type.type = FFI_TYPE_STRUCT
    f_type.elements = elements
    elements[0] = &ffi_type_uint64
    elements[1] = &ffi_type_uint64
    elements[2] = NULL

    self.f_result_type = f_type

.
.
.
.


if (some condition......):
    some code........
else:
    # THIS DOES NOT WORK #
    self._resolve_complex_ffi_type()