Re: GNAT 3.03 and Address Clauses

Re: GNAT 3.03 and Address Clauses

[Robert A Duff]

In article <31850E0F.136C@software.org>,
Rob Pettit  <pettit@software.org> wrote:
>        Device_Data    : Device_Data_Type;   
>        Device_Address : constant System.Address 
>           := System.Storage_Elements.To_Address(16#FFFF_0000#);
>
>        for Device_Data'Address use Device_Address;

>     address_test.ads:13:32: invalid address clause for "Device_Data"
>     address_test.ads:13:32: must be constant defined before "Device_Data" 
>        (RM 13.1(22))

Put Device_Address *before* Device_Data.

- Bob

GNAT 3.03 and Address Clauses

[Rob Pettit]

I have been trying to compile the following code as an example of using the Address 
clause in Ada 95:

     with System.Storage_Elements;     
     package Address_Test is

        type Device_Data_Type is record
           Field_1 : Integer;
           Field_2 : Integer;
        end record;

        Device_Data    : Device_Data_Type;   
        Device_Address : constant System.Address 
           := System.Storage_Elements.To_Address(16#FFFF_0000#);

        for Device_Data'Address use Device_Address;

     end Address_Test;

GNAT 3.03 subsequently gives the following error message:

     address_test.ads:13:32: invalid address clause for "Device_Data"
     address_test.ads:13:32: must be constant defined before "Device_Data" 
        (RM 13.1(22))

Can anyone provide advice for compiling this code using GNAT?
Thanks in advance!

-- Rob Pettit
--------------------------------------------------------------------    
Robert G. Pettit IV     
Member, Technical Staff  
Software Productivity Consortium
2214 Rock Hill Road                     Phone:   703-742-7318
Herndon, VA 22070                       E-Mail:  pettit@software.org
--------------------------------------------------------------------

Re: GNAT 3.03 and Address Clauses

[David Weller]

In article <31850E0F.136C@software.org>,
Rob Pettit  <pettit@software.org> wrote:
[Indicated he was having trouble with this code:]
>        Device_Data    : Device_Data_Type;   
>        Device_Address : constant System.Address 
>           := System.Storage_Elements.To_Address(16#FFFF_0000#);
>
>        for Device_Data'Address use Device_Address;
>
>     end Address_Test;
>
>GNAT 3.03 subsequently gives the following error message:
>     address_test.ads:13:32: invalid address clause for "Device_Data"
>     address_test.ads:13:32: must be constant defined before "Device_Data" 
>        (RM 13.1(22))
>
>Can anyone provide advice for compiling this code using GNAT?
>Thanks in advance!
>


The solution is pretty easy, GNAT's giving you a pretty strong hint:

        Device_Address : constant System.Address
           := System.Storage_Elements.To_Address(16#FFFF_0000#);
        Device_Data    : Device_Data_Type;

        for Device_Data'Address use Device_Address;


Will compile just fine.


(Don't feel too silly, I made the same mistake about a year ago :-)

-- 
    Visit the Ada 95 Booch Components Homepage: www.ocsystems.com/booch
           This is not your father's Ada -- lglwww.epfl.ch/Ada

Re: GNAT 3.03 and Address Clauses

[Robert Dewar]

Dave Weller said

"The solution is pretty easy, GNAT's giving you a pretty strong hint:

        Device_Address : constant System.Address
           := System.Storage_Elements.To_Address(16#FFFF_0000#);
        Device_Data    : Device_Data_Type;

        for Device_Data'Address use Device_Address;"

What happens here is that informally the To_Address call seems like
a static expression, even though it is not technially one. On the list
to do is to specially allow this particular non-static expression in this
context to reduce the number of cases of this kind.