Re: Introductory Ada Programming Book

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

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"Shark8" <onewingedshark@gmail.com> wrote in message 
news:4c5dfbe4-7987-48d4-8afc-817a8c134095@googlegroups.com...
On Wednesday, January 4, 2017 at 6:45:29 AM UTC-7, raph....@gmail.com wrote:
> Le mercredi 4 janvier 2017 13:49:18 UTC+1, Dmitry A. Kazakov a écrit :
>> >
>> > declare
>> >     I : Integer := 1; -- OK
>> >     J : Integer; -- Error: not initialized
>> >     K : Integer := <>; -- OK: uninitialized, I know what I am doing
>> >
>>
>> Or do it Swift's way and use flow analysis to make use of an 
>> uninitialized variable
>> a compile time error. Meh. I guess it's complicated enough as it is to 
>> implement
>> an Ada compiler :)
>
>Well, there are certain times where you *want*/*need* non-initialized 
>variables;
> it's usually at [operating] system-level, but it does exist. (A good 
> example would
> me memory-mapped I/O ports, where your 'initialization' would 
> automatically
> send something down the I/O port when you might need to send nothing.)

Right. It also might happen if the initialization is very complex and 
interrelated with initializing other variables. Forcing an initialization 
just to make the compiler happy would be confusing and potentially expensive 
(if the item is large).

I agree with Dmitry. Indeed, I tried hard in Ada 2005 to get (<>) to be an 
aggregate usable to default initialize for any type, with the intent to 
combine that with a restriction to essentially allow projects to change Ada 
to the rule Dmitry suggested. Unfortunately, various technical issues with 
private types made that much harder than originally thought, and the idea 
was dropped late in the Ada 2005 work.

The problem with requiring flow analysis in a language rule is that it 
requires lengthy specifications of exactly what flow analysis is required 
for this check, assuming that portability between implementations is 
important (and that surely is for Ada). Every compiler does some flow 
analysis, but each it likely to do it differently, in different compiler 
phases, and having program legality be implementation-defined in that way is 
a guaranteed way to have code that cannot be moved to a different 
implementation. (Exception contracts have a similar problem.)

                                         Randy.

The problem with using