Re: Simple program to find average of 3 numbers

["Randy Brukardt" <randy@rrsoftware.com>]

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> Matthew Heaney wrote:
> > With respect to the base range of the type, how do the declarations
> >
> >    type T is new Integer range 1 .. 100;
> >    type T is range 1 .. 100;
> >
> > differ from one another?

For the first, the base type is derived from Integer'Base. So T'Base'First =
Integer'Base'First.

OTOH, all we know about the second T is that T'First <= -100, and T'Last >=
100. (Generally, it is some power of two). Thus, the second gives more power
to the compiler, and thus is preferred.

For instance, Janus/Ada has historically used Integer'Size = 16 (that kept
all of our compilers compatible -- probably a bad choice, but it is
impossible to change without breaking a lot of user code).
    type T1 is Integer range 0 .. 100_000;
       -- Raises Constraint_Error on most versions of Janus/Ada; will work
on GNAT, etc.
    type T2 is range 0 .. 100_000;
       -- Works fine on all modern versions of Janus/Ada.

                        Randy.




> Look at the output from the program I provided.  In the first case, the
> base type has the same characteristics as Integer'Base.  In the second
> example, look at the results of the program I ran.  The compiler can
> choose any predefined integer type for the base type.  In this case,
> GNAT choose one with a range -128..127.
> --
>
>                                                         Robert I. Eachus
>
> �In an ally, considerations of house, clan, planet, race are
> insignificant beside two prime questions, which are: 1. Can he shoot? 2.
> Will he aim at your enemy?� -- from the Laiden novels by Sharon Lee and
> Steve Miller.
>