Re: Side-effect arithmetic again [was: Ada ... in embedded systems]

[stt@henning.camb.inmet.com (Tucker Taft)]

John G. Volan (John_Volan@ccmail.dayton.saic.com) wrote:
: In article <dewar.827845699@schonberg> Robert Dewar, dewar@cs.nyu.edu writes:
: >John Volan said
: >
: >>    procedure Increment (This : in out Item; By: in Positive) is
: >>    begin
: >>      This := Item'Val(Item'Pos(This) + By);
: >>    end Increment;
: >
: >is that it doesn't just limit the "By" parameter to Standard.Positive,
: >it also limits the "This" parameter to possibly a relatively small
: >range of the Item type."
: >
: >Well I can't get particularly upset by that , but if you are, just
: >change this to Item'Val (Item'Pos(This) + Positive'Pos (By)).

: Okay, that leaves the exact type returned by the 'Pos functions
: ambiguous, but what does Ada95 do in that case?  Does it just default
: to Standard.Integer anyway?  (In that case, your answer doesn't really
: solve the problem.) Or can the compiler pick an integer type that's big
: enough?  Or does this simply cause a compilation error?

The 'Pos attribute returns a value of type universal_integer,
which is implicitly convertible to any integer type.  Given that
you are adding it to a value of subtype Positive, it will be
converted to Integer (since Positive is a subtype of Integer).
See RM95 3.5.5(4), 8.6(24), 6.4.1(11).

: ( Name => "John G. Volan", E_Mail => "John_Volan@dayton.saic.com",

-Tucker Taft   stt@inmet.com   http://www.inmet.com/~stt/
Intermetrics, Inc.  Cambridge, MA  USA