Re: Optimizing Boundary Checks

[Peter Amey <peter.amey@praxis-cs.co.uk>]

[snip]
>>
>>How is it if Index_Range was defined as a subtype of Integer?
> 
> 
> Reason for asking is that I get:
> 
> t.adb:10:11: warning: value not in range of subtype of "Standard.integer" defined at line 6
> t.adb:10:11: warning: "constraint_error" will be raised at run time
> 
> if I do:
> 
>    type Items is array (1 .. 10) of Natural;
>    Boxes : Items;
> 
> begin
>    
>    Boxes(11) := 1;
> 
> 

Your array declaration declares an index subtype just as if you had done 
so explicitly with

subtype ItemRange is Integer range 1 ..10;
type Items is array (ItemRange) of Natural;

The array index in your "Boxes..." statement must be in the array index 
subtype and Gnat correctly reports that it isn't.  Gnat can't tell you 
the name of the subtype because you didn't give it one!  This is another 
reason why it is best to avoid use of anonymous types.

Peter