record question

record question

[Alfred Hilscher]

Hi,

assume that I have a record like the one below. I can assign aggregates
in the case that I have subcomponents, but how do I assign if I don't
have?

procedure RT is
  type x (i : Integer := 0) is
    record
      case i is
        when 0 => null;
        when 1..10 => s : STRING (1..10);
        when others => null;
      end case;
    end record;
    
  y : x;
begin
  y := (1, "ABC       ");  -- this is OK
  
  y := (99);   -- but, how do that ?

  y.i := 99;   -- do not work either, so how assign a value different to
1..10 ?
end RT;

Re: record question

[Petter Fryklund]

I'd  try this:

y := (i => 99);

I bet someone else is going to tell why your code is not allowed, but I
don't know.

Alfred Hilscher wrote in message <3BD9618C.D154FE0C@icn.siemens.de>...
>Hi,
>
>assume that I have a record like the one below. I can assign aggregates
>in the case that I have subcomponents, but how do I assign if I don't
>have?
>
>procedure RT is
>  type x (i : Integer := 0) is
>    record
>      case i is
>        when 0 => null;
>        when 1..10 => s : STRING (1..10);
>        when others => null;
>      end case;
>    end record;
>
>  y : x;
>begin
>  y := (1, "ABC       ");  -- this is OK
>
>  y := (99);   -- but, how do that ?
>
>  y.i := 99;   -- do not work either, so how assign a value different to
>1..10 ?
>end RT;

Re: record question

[Claude SIMON]

I think
y := (i => 99);

is better : (99) is an integer expression, not an array nor a record
aggregate.
The same problem arise when you want to pass an array of one element, you
must
write (1=> X).

Claude Simon


Alfred Hilscher a �crit :

> Hi,
>
> assume that I have a record like the one below. I can assign aggregates
> in the case that I have subcomponents, but how do I assign if I don't
> have?
>
> procedure RT is
>   type x (i : Integer := 0) is
>     record
>       case i is
>         when 0 => null;
>         when 1..10 => s : STRING (1..10);
>         when others => null;
>       end case;
>     end record;
>
>   y : x;
> begin
>   y := (1, "ABC       ");  -- this is OK
>
>   y := (99);   -- but, how do that ?
>
>   y.i := 99;   -- do not work either, so how assign a value different to
> 1..10 ?
> end RT;

Re: record question

[Ted Dennison]

In article <9rbne9$sa7$1@newstoo.ericsson.se>, Petter Fryklund says...
>
>I'd  try this:
>
>y := (i => 99);

Its the same issue with arrays. If you have multiple elements then (1, 2, 3)
will work. But if you don't, then (1) will not. Instead, you have to do
something like (1 => 1).

Of course for those of us who always use named-notation anyway, this isn't so
confusing. :-)

---
T.E.D.    homepage   - http://www.telepath.com/dennison/Ted/TED.html

No trees were killed in the sending of this message. 
However a large number of electrons were terribly inconvenienced.

Re: record question

[Ted Dennison]

In article <3BD96844.699A15BC@setra.fr>, Claude SIMON says...
>The same problem arise when you want to pass an array of one element, you
>must
>write (1=> X).

..and for an array of 0 elements (yes, those can exist), it would be (others =>
Whatever)  (replace "Whatever" with a placebo expression of the appropriate
type).

---
T.E.D.    homepage   - http://www.telepath.com/dennison/Ted/TED.html

No trees were killed in the sending of this message. 
However a large number of electrons were terribly inconvenienced.

Re: record question

[Claude SIMON]

In general (when it make sense) when I declare an array, I declare a constant of
that array type with
an empty range of  any (may be empty) value. That constant is used in place of a 0
elements aggregate.

Claude Simon

Ted Dennison a �crit :

> In article <3BD96844.699A15BC@setra.fr>, Claude SIMON says...
> >The same problem arise when you want to pass an array of one element, you
> >must
> >write (1=> X).
>
> ..and for an array of 0 elements (yes, those can exist), it would be (others =>
> Whatever)  (replace "Whatever" with a placebo expression of the appropriate
> type).
>
> ---
> T.E.D.    homepage   - http://www.telepath.com/dennison/Ted/TED.html
>
> No trees were killed in the sending of this message.
> However a large number of electrons were terribly inconvenienced.

Re: record question

[Richard Pinkall-Pollei]

>assume that I have a record like the one below. I can assign aggregates
>in the case that I have subcomponents, but how do I assign if I don't
>have?
>
> [code example moved to end of message for reference]

The record type you are using is "mutable", since it has a default
discriminant.  Thus, you can change the discriminant, but only if you
provide a complete record or aggregate in the assignment.  Thus, you
would have to use "y := ( i => 99 ) ;" since it assigns a complete
aggregate (since "i" is the only component for this discriminant
value).  You cannot use the "y.i" form, since that would technically
only assign a single component, even though the record has only one
component.

I ran your code fragment through the GNAT 3.13p compiler, just to see
if it was smart enough to realize that "y.i" was, in fact, the only
record component.  The error message resulting from the "y.i"
assignment states that the left hand of the assignment must be a
variable.  I would say that's not the real problem, but I'm not sure
why GNAT flags it this way.

>procedure RT is
>  type x (i : Integer := 0) is
>    record
>      case i is
>        when 0 => null;
>        when 1..10 => s : STRING (1..10);
>        when others => null;
>      end case;
>    end record;
>    
>  y : x;
>begin
>  y := (1, "ABC       ");  -- this is OK
>  
>  y := (99);   -- but, how do that ?
>
>  y.i := 99;   -- do not work either, so how assign a value different to
>1..10 ?
>end RT;


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Re: record question

[Jeffrey Carter]

Alfred Hilscher wrote:
> 
> procedure RT is
>   type x (i : Integer := 0) is
>     record
>       case i is
>         when 0 => null;
>         when 1..10 => s : STRING (1..10);
>         when others => null;
>       end case;
>     end record;
> 
>   y : x;
> begin
>   y := (1, "ABC       ");  -- this is OK
> 
>   y := (99);   -- but, how do that ?
> 
>   y.i := 99;   -- do not work either, so how assign a value different to
> 1..10 ?
> end RT;

(99) is a parenthesized expression, not an aggregate. An aggregate of
one value must use named notation:

(I => 99)

You may only change a discriminant of an unconstrained record variable
by assigning the entire record at once. Since I is a discriminant of
type X, "Y.I := ..." is illegal.

Thus, you must write:

Y := (I => 99);

-- 
Jeff Carter
"I wave my private parts at your aunties."
Monty Python & the Holy Grail