Re: Syntax question: new with a constrained subtype indication

["Alex R. Mosteo" <devnull@mailinator.com>]

James Alan Farrell wrote:
> Hi all,
> I'm working on software to analyze Ada programs using ASIS.  As such I 
> need to make sure I handle all cases in the syntax (and I'm finding that 
> in past assignments I've used only a small portion of the whole language!)
> 
> I'm currently working on a piece of code to analyze allocator 
> expressions (ARM 4.8).  The entire relevant syntax is:
> 
>  4.8:
>  allocator ::=
>     new subtype_indication | new qualified_expression
> 
>  3.2.2:
>  subtype_indication ::=  subtype_mark [constraint]
> 
>  3.2.2:
>  subtype_mark ::= subtype_name
> 
>  3.2.2:
>  constraint ::= scalar_constraint | composite_constraint
> 
>  3.2.2:
>  scalar_constraint ::=
>       range_constraint | digits_constraint | delta_constraint
> 
>  3.5
>  range_constraint ::= range range
> 
>  3.5:
>  range ::=  range_attribute_reference
>    | simple_expression .. simple_expression
> 
>  From this, it appears I should be able to do something like:
> 
> package body Mod1 is
> 
>    procedure Proc1 is
> 
>       type Vector    is array (Integer range <>) of Float;
>       type VectorPtr is access Vector;
> 
>       V : VectorPtr;
> 
>    begin
>       V := new Vector range 1 .. 10;

What I've done quite frequently is

V := new Vector (1 .. 10);

>    end Proc1;
> 
> end mod1;
> 
> Using gnat 3.15p, I get this error:
> 
> mod1.adb:15:23: incorrect constraint for this kind of type
> gnatmake: "mod1.adb" compilation error
> 
> I suspect this is a type issue, but let me know if there is something 
> incorrect in the syntax.
> 
> The thing is, I've read 4.8 of the *annotated* ARM and I don't see 
> anything to say I cannot do this.  So what am I missing?  Is there 
> something, other than that document, that spells out the allowed types 
> of constraint?
> 
> Thank you,
> James Alan Farrell