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From: "Jeffrey R. Carter" <spam.not.jrcarter@acm.not.spam.org>
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Subject: Re: To collection (GNAT bug)
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Dmitry A. Kazakov wrote:
> 
> No. These aren't equivalent. In many cases the programmer does not know
> what he is doing on the level of bits and bytes. Otherwise he probably
> wouldn't instantiate Unchecked_Conversion, but wrote a conversion of his
> own. He only knows the semantics of an object and asks the compiler to
> convert the types according to this semantics. It is a deal - the
> programmer knows the semantics, the compiler does the representation.

I think you misunderstand the meaning of unchecked. 'Unchecked_Access 
tells the compiler that this access value will not violate the 
accessibility rules, even though the compiler thinks it will. 
Unchecked_Deallocation tells the compiler that there are no other 
references to this designated object, even if there are. And 
Unchecked_Conversion means to interpret the bit pattern starting with 
the bits of this value as being of that type, whether it makes sense or 
not. It does not involve a change of representation. In terms of object 
code, Unchecked_Deallocation does nothing; it merely provides a way 
around the restrictions of the language.

-- 
Jeff Carter
"You empty-headed animal-food-trough wiper."
Monty Python & the Holy Grail
04