Re: Zero length Objects

[Jeffrey Carter <spam@spam.com>]

Nick Roberts wrote:

> As far as I am aware, the Ada standard permits types, subtypes, and
> objects of zero size. I think that X'Size must return 0 if it has
> been set to 0 (by a representation clause) for any subtype or object
> X, but there is nothing in the standard to prevent objects of zero
> size being allocated more than zero bits when they are allocated in
> memory (and I gather this is what many compilers actually do).

The 'Size of an object need not be the same as the subtype 'Size. For
example, on many systems, Integer'Size = 32, Natural'Size = 31. For

N : Natural;

N'Size is usually 32. 31 comes into play in situations such as packed types.

Similarly, for

type Size_2 is (One, Two, Three, Four);
for Size_2'Size use 2;

S : Size_2;

S'Size is usually 8.

-- 
Jeff Carter
"I'm a lumberjack and I'm OK."
Monty Python's Flying Circus
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