Re: Interface/Implementation (was Re: Design by Contract)

["Samuel T. Harris" <s_harris@hso.link.com>]

Marc Wachowitz wrote:
> 
> Joachim Durchholz <joachim.durchholz@munich.netsurf.de> wrote:
> > Ada, if we have a name clash, we're forced to
> > type the full module name wherever a clashing name is used (at least
> > that's what I remember, corrections welcome!).
> 
> If you merely import a package, by means of a "with" clause, you cannot
> get any name clashes at all, no matter what's in the package, since every
> reference is qualified with the package name.
> 
> If you don't like some name, e.g. of a package or a type or a variable or
> a routine or an exception, you can introduce another name for it (which
> may be local, but can also be exported by a package). This can as well be
> used to introduce non-qualified names specifically for that imported stuff
> which you want, without being bothered by whatever else the package exports,
> or might export in the future.

For Joachim's benefit, this is done via a renaming declaration for
packages, subprograms, and variables; and a subtype for types.
There are no renames declarations for types.

> 
> Only if you really call for it, by means of a "use" clause, all the stuff
> exported by an imported package will become visible in the client's scope,
> and thus be a potential source for name clashes (for routines only where
> overloading can't resolve the conflict). Many people don't like use-clauses,
> and some projects don't allow them. They are never necessary at all, only a
> way to reduce typing (i.e. on the keybord, this isn't about type checking).
> 
> -- Marc Wachowitz <mw@ipx2.rz.uni-mannheim.de>

Again, to expand. It is useful to use 'use' clauses to achieve
visibility
to the operations for direct use in expressions. Conservative projects
which frown on "use" clauses in the context usually allow "use" clauses
in the limited declarative scope of subprograms and block statements.
While this does introduce multiple "use" clauses everywhere they are
needed, such a convention does limited the potential for "problems"
with global use of "use".

-- 
Samuel T. Harris, Senior Engineer
Hughes Training, Inc. - Houston Operations
2224 Bay Area Blvd. Houston, TX 77058-2099
"If you can make it, We can fake it!"