Access-to-Constant parameters

[m_cubed@my-deja.com]

Ada provides access-to-variable parameters in
operation signatures which allow dispatching.
For example:

type State Type is tagged private;

Set_Exercise_Mode (
  State_Ptr: access State_Type;
  Exercise_Mode: in Exercise_Mode_Type);

What it doesn't seem to provide is
access-to-constant parameters for dispatching
operations. For example, it would be useful to
do the following to ensure that the query doesn't
update the object being queried (hypothetical
syntax):

function Exercise_Mode (
  State_Ptr: access constant State_Type)
  return Exercise_Mode_Type;

Is there any way of doing this, or am I forced
to sacrifice dispatching by using a specific
access-to-constant type as the formal parameter?
For example:

type State_Type is tagged private;

type RO_Access_State_Type is
  access constant State_Type;

function Exercise_Mode (
  State_Ptr: RO_Access_State_Type)
  return Exercise_Mode_Type;


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