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Subject: Re: Type_Invariant and instance creation
References: <slrnlsg4lu.i0l.lithiumcat@nat.rebma.instinctive.eu>
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On 21-Jul-14 17:29, Randy Brukardt wrote:
> I'd guess that both are wrong, although it may not have to do with this
> example.:-)  There's lots of issues with Type_Invariant (it seems SO
> simple); we've pretty much given up on making it bullet-proof. We just
> approved yet another AI on the topic (AI12-0042-1/09 -- 8 versions before
> this one!) and I suspect that we haven't found all of the problems. Both
> predicates and postconditions are in better shape, so I'd use them more than
> type invariants.


That's disappointing to hear.
I was poking around the WordPerfect SDK [WPD format], and was thinking 
Type_Invariant would be perfect for that.


     Type File_Header is record
         Padding_Prefix	: Interfaces.Unsigned_8;
         Signature	: String(1..3);
         Document_Offset	: Interfaces.Unsigned_32;
         --Product : Product_Type;
         Document_Type	: File_Types;
     end record
     with Type_Invariant =>
         File_Header.Padding_Prefix = 16#FF#
AND	File_Header.Signature = "WPC";