Re: Position of "use"

[Victor Porton <porton@narod.ru>]

Adam Beneschan wrote:
> On Friday, July 4, 2014 11:43:46 PM UTC-7, Victor Porton wrote:
>> What is the difference between
>> 
>> with X; use X;
>> package Y is
>> end Y;
>> 
>> and
>> 
>> with X;
>> package Y is
>>    use X;
>> end Y;
>> 
>> ?
> 
> OK, I've looked into it, and there's no difference.  I'm assuming that
> there may be more code in the specification of Y, but that in the second
> example, "use X" is the first thing in this specification.
> 
> RM 8.4(6-7) describe the "scope" of a use_clause, which is the portion of
> code that is affected by the "use".  If it's in the context clause, the
> scope is the entire declarative region of the package.  If it's inside the
> declarative region, the scope is the part of the declarative region
> starting from the "use" and ending at the end of the declarative region;
> if the "use" clause is the first thing in the region (as in the second
> example above), that means that the scope is the entire declarative region
> of the package, same as the first example.  (Note that in both cases, the
> declarative region will include child packages, if any.  This follows from
> the rules in RM 8.1.)
> 
> The scope doesn't include the context clause itself.  (The context clause
> is the "with" and "use" statements that occur before the
> "package/procedure/function" of a top-level library unit, and it may
> include pragmas.)  RM 10.1.6 says that the visibility rules don't apply to
> the context clause, and it contains special rules for context clauses. 
> Nothing in those rules says that "use" makes anything visible in a context
> clause; therefore, a "use" in a context clause has no effect on any other
> "with", "use", or "pragma" in the context clause, or in any other context
> clause (i.e. the context clause on a child package or subunit).
> 
> Therefore, the effect of a "use" that is the first thing in a package
> specification has the exact same effect as a "use" appearing in the
> context clause.
> 
>                            -- Adam

Possible reason why these two equal variants of syntax were introduced by 
Ada designers:

It would be different if we'd replace package with a procedure or a 
function, because use can apply or not apply to procedure parameters.

The same applies to generic packages.

-- 
Victor Porton - http://portonvictor.org