* Re: what is happening here? (access types & discriminants...)
2000-03-19 0:00 what is happening here? (access types & discriminants...) Dale Stanbrough
2000-03-19 0:00 ` Robert Dewar
@ 2000-03-19 0:00 ` Simon Wright
1 sibling, 0 replies; 5+ messages in thread
From: Simon Wright @ 2000-03-19 0:00 UTC (permalink / raw)
dale@cs.rmit.edu.au (Dale Stanbrough) writes:
> I've got the equivalent of the following code...
>
> with ada.strings.unbounded; use ada.strings.unbounded;
>
> package ua is
> type Unbounded_Array is array (Positive range <>) of Unbounded_String;
> type Unbounded_Array_Ptr is access Unbounded_Array;
>
>
> i_dont_understand : unbounded_Array_ptr (1..100);
> end ua;
>
>
> Not quite sure what the definition of i_dont_understand is doing...
Judging by this experiment,
with Ada.Strings.Unbounded; use Ada.Strings.Unbounded;
with Ada.Text_Io; use Ada.Text_Io;
procedure Ua is
type Unbounded_Array is array (Positive range <>) of Unbounded_String;
type Unbounded_Array_Ptr is access Unbounded_Array;
I_Dont_Understand : Unbounded_Array_Ptr (13 .. 42)
:= new Unbounded_Array (13 .. 42);
Me_Neither : Unbounded_Array_Ptr
:= new Unbounded_Array (14 .. 43);
begin
Put_Line ("f" & I_Dont_Understand'First'Img &
" l" & I_Dont_Understand'Last'Img);
Put_Line ("f" & Me_Neither'First'Img &
" l" & Me_Neither'Last'Img);
-- I_Dont_Understand := Me_Neither; ------------------ CE
-- Put_Line ("f" & I_Dont_Understand'First'Img &
-- " l" & I_Dont_Understand'Last'Img);
I_Dont_Understand.all := Me_Neither.all;
Put_Line ("f" & I_Dont_Understand'First'Img &
" l" & I_Dont_Understand'Last'Img);
Me_Neither := new Unbounded_Array (13 .. 43);
Put_Line ("f" & Me_Neither'First'Img &
" l" & Me_Neither'Last'Img);
end Ua;
where the commented-out bit raises Constraint_Error, we've declared
i_dont_understand as a pointer capable of pointing only to arrays with
the designated constraint.
So an array assignment (of the right length) is OK, but a pointer
assignment with different constraints isn't.
^ permalink raw reply [flat|nested] 5+ messages in thread
* what is happening here? (access types & discriminants...)
@ 2000-03-19 0:00 Dale Stanbrough
2000-03-19 0:00 ` Robert Dewar
2000-03-19 0:00 ` Simon Wright
0 siblings, 2 replies; 5+ messages in thread
From: Dale Stanbrough @ 2000-03-19 0:00 UTC (permalink / raw)
I've got the equivalent of the following code...
with ada.strings.unbounded; use ada.strings.unbounded;
package ua is
type Unbounded_Array is array (Positive range <>) of Unbounded_String;
type Unbounded_Array_Ptr is access Unbounded_Array;
i_dont_understand : unbounded_Array_ptr (1..100);
end ua;
Not quite sure what the definition of i_dont_understand is doing...
Thanks,
Dale
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: what is happening here? (access types & discriminants...)
2000-03-19 0:00 what is happening here? (access types & discriminants...) Dale Stanbrough
@ 2000-03-19 0:00 ` Robert Dewar
2000-03-20 0:00 ` Dale Stanbrough
2000-03-19 0:00 ` Simon Wright
1 sibling, 1 reply; 5+ messages in thread
From: Robert Dewar @ 2000-03-19 0:00 UTC (permalink / raw)
In article <dale-1903002134440001@192.168.0.2>,
dale@cs.rmit.edu.au (Dale Stanbrough) wrote:
> i_dont_understand : unbounded_Array_ptr (1..100);
> end ua;
>
> Not quite sure what the definition of i_dont_understand is
doing...
Not quite clear what you are asking, this is simply a
constrained subtype, no different conceptually from
x : integer range 1 .. 100;
Sent via Deja.com http://www.deja.com/
Before you buy.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: what is happening here? (access types & discriminants...)
2000-03-19 0:00 ` Robert Dewar
@ 2000-03-20 0:00 ` Dale Stanbrough
2000-03-21 0:00 ` Robert Dewar
0 siblings, 1 reply; 5+ messages in thread
From: Dale Stanbrough @ 2000-03-20 0:00 UTC (permalink / raw)
Robert Dewar wrote:
> Not quite clear what you are asking, this is simply a
> constrained subtype, no different conceptually from
>
> x : integer range 1 .. 100;
Does the declartion cause the pointer to only be able to point
at arrays from 1..100? If so I didn't know you could constrain
pointers in such a way.
Dale
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: what is happening here? (access types & discriminants...)
2000-03-20 0:00 ` Dale Stanbrough
@ 2000-03-21 0:00 ` Robert Dewar
0 siblings, 0 replies; 5+ messages in thread
From: Robert Dewar @ 2000-03-21 0:00 UTC (permalink / raw)
In article <dale-2003000749300001@192.168.0.2>,
dale@cs.rmit.edu.au (Dale Stanbrough) wrote:
> Does the declartion cause the pointer to only be able to point
> at arrays from 1..100?
yes
> If so I didn't know you could constrain
> pointers in such a way.
It is a standard Ada 83 feature ...
Sent via Deja.com http://www.deja.com/
Before you buy.
^ permalink raw reply [flat|nested] 5+ messages in thread
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2000-03-19 0:00 what is happening here? (access types & discriminants...) Dale Stanbrough
2000-03-19 0:00 ` Robert Dewar
2000-03-20 0:00 ` Dale Stanbrough
2000-03-21 0:00 ` Robert Dewar
2000-03-19 0:00 ` Simon Wright
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