Re: Syntax question: new with a constrained subtype indication

[Martin Krischik <krischik@users.sourceforge.net>]

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;

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

or shorter:

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

You mixed the syntax for integer types:

http://en.wikibooks.org/wiki/Programming:Ada:Types:range

with the one for arrays

http://en.wikibooks.org/wiki/Programming:Ada:Types:array

The later need the ( and ).

>     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?

Your idea was right - just a syntax problem.

Have fun

Martin 

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