Request for help from the ARG: Static constants

Request for help from the ARG: Static constants

[Randy Brukardt]

There is a language-lawyer level question that some of the ARG members have 
been discussing privately for far too long in the past week. An important 
part of the question is the compatibility effect of changing the rules to 
match the expectation. As such, I'd like to find out what various compilers 
do on the following test program. I've tried recent versions of GNAT and 
Janus/Ada, both of which reject the program citing an error at (2). [This is 
not supported by the RM wording, BTW.] If you have access to some other Ada 
compiler, please attempt to compile this program and report the result, 
either here or to me privately (randy@rrsoftware.com).

                       Randy Brukardt, ARG Editor.

--- Cut here ---

with Ada.Text_IO;
procedure SC is
   Item_Size : constant := 0;
begin
   Ada.Text_IO.Put_Line ("Start Static Constant check");
   if Item_Size > 0 then
      declare
         Length : Positive := Item_Size; -- (1)
         type Data_Index is range 1 .. Length; -- (2)
         type Data_Array is array (Data_Index) of Natural;
      begin
         Ada.Text_IO.Put_Line ("Can't get here");
      exception
         when Constraint_Error =>
            Ada.Text_IO.Put_Line ("Can't get here, either");
      end;
   else -- Do nothing
      Ada.Text_IO.Put_Line ("Nothing as expected");
   end if;
   Ada.Text_IO.Put_Line ("End Static Constant check.");
end SC;

Re: Request for help from the ARG: Static constants

[Randy Brukardt]

Tucker Taft has pointed out that I left out the keyword "constant" from my 
test program, which makes a big difference! Please try the corrected program 
below:

> There is a language-lawyer level question that some of the ARG members 
> have been discussing privately for far too long in the past week. An 
> important part of the question is the compatibility effect of changing the 
> rules to match the expectation. As such, I'd like to find out what various 
> compilers do on the following test program. I've tried recent versions of 
> GNAT and Janus/Ada, both of which reject the program citing an error at 
> (2). [This is not supported by the RM wording, BTW.] If you have access to 
> some other Ada compiler, please attempt to compile this program and report 
> the result, either here or to me privately (randy@rrsoftware.com).
>
>                       Randy Brukardt, ARG Editor.
>
> --- Cut here ---

with Ada.Text_IO;
procedure SC is
  Item_Size : constant := 0;
begin
  Ada.Text_IO.Put_Line ("Start Static Constant check");
  if Item_Size > 0 then
     declare
        Length : constant Positive := Item_Size; -- (1)
        type Data_Index is range 1 .. Length; -- (2)
        type Data_Array is array (Data_Index) of Natural;
     begin
        Ada.Text_IO.Put_Line ("Can't get here");
     exception
        when Constraint_Error =>
           Ada.Text_IO.Put_Line ("Can't get here, either");
     end;
  else -- Do nothing
     Ada.Text_IO.Put_Line ("Nothing as expected");
  end if;
  Ada.Text_IO.Put_Line ("End Static Constant check.");
end SC;

Re: Request for help from the ARG: Static constants

[tmoran]

> (2). [This is not supported by the RM wording, BTW.] If you have access to
> some other Ada compiler, please attempt to compile this program and report

An ancient ObjectAda compiler gives:

--------------------Target: Win32 (Intel) Debug--------------------
sc.adb: Warning: line 8 col 39 LRM:11.5(17), Value outside range, Constraint_Error will be raised

Front end of f:\oa722\console\sc.adb succeeded with no errors.
Tool execution has completed.