c_element_type now raises MethodNotDefined.

theano/gof/op.py

@@ -1406,9 +1406,10 @@ class COp(Op):
             wrapper = self.params_type
             params = [('APPLY_SPECIFIC_WRAPPER', wrapper.name)]
             for i in range(wrapper.length):
-                field_c_element_type = wrapper.types[i].c_element_type()
-                if field_c_element_type:
-                    params.append(('DTYPE_PARAM_' + wrapper.fields[i], field_c_element_type))
+                try:
+                    params.append(('DTYPE_PARAM_' + wrapper.fields[i], wrapper.types[i].c_element_type()))
+                except utils.MethodNotDefined:
+                    pass
             return params
         return []
 

theano/gof/type.py

@@ -46,7 +46,7 @@ class CLinkerType(CLinkerObject):
          - For ``GpuArrayType(dtype='int32', ...)``: should return ``"ga_int"``.
 
         """
-        return ''
+        raise MethodNotDefined("c_element_type", type(self), self.__class__.__name__)
 
     def c_is_simple(self):
         """