[Dwarf-Discuss] About self-referencial sized types

Pierre-Marie de Rodat derodat at adacore.com
Tue Jun 10 02:30:01 PDT 2014


Todd,

On 05/27/2014 06:16 PM, Todd Allen wrote:
> Sorry for the last response on this.  But perhaps an example from our Ada
> compiler will help you.

Well, thank you very much for this!

> Anyway, the significant thing is that we're not referencing "n" directly, but
> rather the stored values for the upper bound.  If you store the result of
> max(0,n) somewhere, you could reference it directly.  For the case of general
> expression upper bounds, you'd have to store the values somewhere (freeze them)
> in case they might produce different results on subsequent evaluations.  But I
> don't know if the max(0,n) might be a special case where you don't do that.

That's interesting. Unfortunately, we do not store the value of the 
upper bounds in the record (nor anywhere else): the only way to get it 
at runtime is to compute it from the discriminants. The discriminants 
are the only runtime arguments that can determine the array bounds, so 
there is no risk that the bound expressions would produce different 
results sometimes.

-- 
Pierre-Marie de Rodat


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