Re: using `use' : what is the best practice ?

[Simon Wright <simon@pushface.org>]

milouz <a.michelizza@gmail.com> writes:

> Hi guys,

> Maybe a not so anecdotic question : when using the 'use' clause ?
>
> My first thought is that using 'use' is not good because it masks the
> package tree.

100% agree.

Well, actually more like 90%! I have no problem writing

   with Ada.Text_IO; use Ada.Text_IO;

(but, I'd most often be using Text_IO for debug trace output, not in
operational code).

And some packages (Ada.Strings.Unbounded) are designed to be "use"d.

AdaCore tend to use package renaming, eg

   package SSE renames System.Storage_Elements;

> For example, if I have 2 packages with procedures sharing the same
> name, example `P1.Foo' and `P2.Foo', my code won't be very readable if
> I only write the short name (`Foo') :
>
>    with P1; use P1;
>    with P2; use P2;
>
>    procedure Main is
>       My_Val : Integer;
>    begin
>       Foo(My_Val);  -- P1 or P2 ?

And would not even compile, if both packages contained a procedure Foo.

> But always avoiding 'use' give some rather obfuscated code, especially
> when using some specific arithmetic operator. For example, playing
> with Address arithmetic without 'use' :
> System.Storage_Elements."+"(System.Storage_Elements.Storage_Offset(N),
> A);

See "use type", designed for exactly this purpose.

http://www.adaic.org/resources/add_content/standards/05rm/html/RM-8-4.html#I3407

Although you can "use type" in the context clauses (the "with"s) I much
prefer to put them as close as possible to the actual use: eg, in the
declarative region of a subprogram.

Of course, if all the subprograms in a package need to "use type", move
the "use type" to package scope.