Re: Syntax question: new with a constrained subtype indication

[James Alan Farrell <jfarrell@grammatech.com>]

Martin Krischik wrote:

Yes, I see it now.  Thanks.

> 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 
>