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From: dennison@telepath.com
Subject: Re: win32ada design question/problem
Date: 1998/11/18
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Date: 1998-11-18T00:00:00+00:00
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In article <36531538.483857@SantaClara01.news.InterNex.Net>,
  tmoran@bix.com (Tom Moran) wrote:
> >I think a binding done with System.Address for pointers and strings, and
> >Interfaces.C.Int for integers, would be far better.
>   Why exactly is X'Address preferable to X'Unchecked_Access?
>   Having spent a fair amount of time in the past debugging/correcting
> supposedly portable code that incorrectly assumed an access type was a
> 'Address, I'm rather sensitive to this issue.

Its preferable philosophicly when I don't know and don't *care* what type of
object it points to, other than possibly its size. This is often the case in C
bindings and OS calls.

With access objects I have three choices:
  o  Write one binding for each C-routine/passed object combination I will
     ever want to use.
     Clearly unacceptable.

  o  Arbitrarily pick some dummy access type to use for the C-routine, and
convert other accesses and addresses into it.
     In keeping with the C approach, but Evil. Can cause confusion for
maintainers and other readers, and thus may cause bugs in the future.

  o  Create and use some unconstrained data array access object.  Not evil.
But unchecked conversion or address_to_access_conversion is still required to
get a value of this type. Careless attempts to dereference the pointer may
cause problems due to lack of bounds information. Way more work than using
Address.

--
T.E.D.

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