"Peter Amey" <peter.amey@praxis-cs.co.uk> a �crit dans le message de news:bl18e1$6ot2h$1@ID-69815.news.uni-berlin.de...
> Some guidance please to reduce the slight panic I am suffering from.
>
> When reading in values from an external device it is important to check
> that the value read is a valid representation for its type.  The read
> values are also considered volatile so each read returns a potentially
> different value.
> [...]

> (Horrible strawman solution: do an unchecked conversion of External_Port
> into Temp and then do the validity check).
>
Not a horrible solution. You cannot assume your value is a T until you have checked
for it!
As long as all you know is that it is a set of bits, put it in a variable appropriate for
sets of bits. *After* validity checking, you can consider it a T. And Unchecked_Conversion
is the appropriate tool for changing the view on a give set of bits.

-- 
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           J-P. Rosen (rosen@adalog.fr)
Visit Adalog's web site at http://www.adalog.fr