Re: with and use

["Jeffrey D. Cherry" <yrrehcdj@hcetu.ten>]

[-- Warning: decoded text below may be mangled, UTF-8 assumed --]
[-- Attachment #1: Type: text/plain, Size: 2649 bytes --]

David Rasmussen <pinkfloydhomer@yahoo.com> wrote in news:3D2C3A69.8070207
@yahoo.com:

> Jean-Pierre Rosen wrote:
> > "David Rasmussen" <pinkfloydhomer@yahoo.com> a �crit dans le message
> > news: 3D2C2FF9.4020300@yahoo.com...
> >

<snip>

> >> Secondly, where is with and use typically used, and what is the
> >> difference between them?
> >>
> >
> > A with clause means that a compilation unit needs the services from
> > another *compilation unit* (i.e. a package, subprogram or generic
> > which is separately compiled).
> >
> > A use clause factors out a *package*, i.e. you don't have to repeat
> > the package name in front of every element. Since a package can (but
> > needs not) be a compilation unit, there are cases where both clauses
> > can be applied, but they are really orthogonals.
> >
> 
> So with corresponds roughly to an #include of some header file that 
> defines prototypes etc. for some other compilation unit in C++, and use 
> corresponds roughly to "using namespace Whatever", assuming that the 
> things included were in a seperate namespace?
> 
> "with" and only appear at the top of a unit. Where can "use" appear?
> 
> /David
> 

You are quite correct here to associate the Ada "use" clause with the C++ 
"using namespace" using-directive.  You are also reasonably correct regarding 
the "with" clause, but I would qualify the C++ equivalent a bit further.  I 
would say the Ada "with" clause more closely corresponds to a #include of 
some header file that defines a namespace containing function prototypes 
and/or other declarations.

The Ada "with" clause should appear in what would be the C++ global scope if 
C++ were limited to a single class, namespace, or function per translation 
unit.  The Ada "use" clause can appear in what would be the C++ global scope 
or in the C++ block scope.

One final note would be that the Ada "use" clause is only valid for packages.  
It cannot be used for a "with"ed subpgrogram or generic unit.  If the generic 
unit is a package, the "use" clause can be issued after the instantiation.  
For example:

   with Some_Generic_Package;

   procedure Main is

      package Instance is new Some_Generic_Package( ... );
      use Instance;

   begin -- Main
      null;
   end Main;

This shows the "with" clause pulling a generic package (a C++ template unit) 
into the Main procedure's context, instantiating the package in the 
declarative region, and then making the contents of the new package directly 
visible via a "use" clause (in a C++ block scope).

Hope that helps!


-- 
Regards,
Jeffrey D. Cherry
Senior IV&V Analyst
Northrop Grumman Information Technology