Re: Clause "with and use"

["Robert I. Eachus" <rieachus@comcast.net>]

Russ wrote:

> Not being an Ada programmer, I did not even know off the top of my
> head that "with Foo.Bar" is illegal. I'm at work, and my Ada books are
> at home, so let me ask a "newbie" question. Am I correct in assuming
> that "use Foo.Bar" *must* be preceded by "with Foo"? More
> specifically, am I correct in assuming that "use Foo.<anything>"
> *must* be preceded by "with Foo"?
> 
> If so, then the solution seems trivial to me. Let any occurence of
> "use Foo.<anything>" in the context section imply "with Foo". That is,
> for any "use" in the context section, simply take its argument and
> strip off the first "." and anything that follows it, then use that as
> the argument to the implied "with".

Unfortunately, it is not that simple.  You can with library units, and 
child packages are library units, while nested packages are not, so 
whether or not with Foo.Bar is legal in theory requires semantic 
analysis, and in practice requires searching the compilation 
environment.  So when you say "with Ada.Text_IO; use Ada.Text_IO;" yes 
there is an (implied) with of Ada, but there is also a with of 
Ada.Text_IO; then the use clause currently ONLY applies to Ada.Text_IO, 
not to Ada.  That is one of the differences I have been talking about.

> If not, I guess I just made a fool of myself. Oh well.

Just the opposite.  Now you are beginning to participate in the real 
discussion of this issue.  Personally, I don't even use a keyboard 
shortcut for the "with Ada.Text_IO; use Ada.Text_IO;" case.  I type fast 
enough, and that is one of the cases where I often do have a use clause 
in the context clause.  In fact, sometimes I get exactly that far then 
spend sometime thinking.  Do I want to create a generic template now, or 
deal with this I/O package separately?  Do I want this package to be the 
child of something, or standalone, etc.

But if there is a problem here, what we need to understand is both what 
are we trying to fix--if anything--and what are the problems that a fix 
must avoid creating.  For me, there are many packages that are 
descendents of Ada for which I almost automatically put a use clause in 
the context clause.  (There are others, such as Ada.Strings.Bounded 
where the use clause has to be for the instance I create.  Since I tend 
to instantiate them inside other library units, the use clause often 
can't go in the context clause.)  But for library units not in Ada, I 
tend to avoid use clauses in context clauses.  Add to that my typing 
speed, and as I said I don't have a problem with the current rules. 
Doesn't mean that others don't, and I certainly won't be opposed to an 
extension that has no significant drawbacks.  I might feel that there 
are other problems that are more pressing--for example the issue of 
mutually dependent abstractions--but that is an issue of prioritization.

-- 
                                           Robert I. Eachus

100% Ada, no bugs--the only way to create software.