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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: Teaching C/C++ from Ada perspective?
Date: Wed, 04 Jul 2018 17:01:07 +0100
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Xref: reader02.eternal-september.org comp.lang.ada:53599
Date: 2018-07-04T17:01:07+01:00
List-Id: <comp.lang.ada>

Maciej Sobczak <see.my.homepage@gmail.com> writes:

>> > Yet, the trivial update of P (like adding whitespace, which again has
>> > no semantic meaning whatsoever) forces the recompilation of Test (with
>> > GNAT). Actually, it forces the recompilation of everything. Why?
>> 
>> gprbuild:
>>   -m       Minimum Ada recompilation
>> 
>> Only rebuild if there's a semantic difference
>
> Great! Let's try it out.
> I have added a dummy declaration to P, like here:
>
> -- p.ads:
> package P is
>    pragma Pure (P);
>    type TI is new Integer;  -- new dummy definition
> end P;
>
> and... the whole project was recompiled from scratch.
>
> No other part of the project relies on this new type and in
> particular, the author of Test still could not care less about package
> P and whatever it contains.
> Yet, the author of Test had to wait for the whole project to
> recompile, because something irrelevant was added to some irrelevant
> package that he might not even know that exists in the project.
>
> I presume that the -m switch was supposed to handle a trivial (and
> perhaps frequent) case of editing comments and whitespace. There is
> some added value in this, but it is easy to replicate for C++ and
> sorry, but I don't call it "semantic" if it cannot figure out even the
> most basic cases like the one above.

I think we'll have to agree to differ on what "semantic" means, then.

> My claim that Ada and C++ compilers have the same challenges when it
> comes to handling the physical project structure holds.

Indeed.