Re: Running a preprocessor from GPS?

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Fri, 31 Jul 2015 11:20:35 -0700 (PDT), EGarrulo wrote:

> On Friday, July 31, 2015 at 7:54:52 PM UTC+2, Jeffrey R. Carter wrote:
>> Many of the "design patterns" are actually implementation patterns to work
>> around deficiencies in the languages used in the book. An obvious example is the
>> "singleton pattern". In Ada, a singleton is simply a pkg. It's only a problem
>> that needs a pattern in languages that lack modules.
> 
> But a singleton would be instantiated when the "Get_Instance" function gets
> called by client code, not when a module gets loaded.  Or does Ada load a package
> at the first call?

Well, since other responses regarding singletons were IMO wrong. Here is an
answer from the OO POV.

In Ada singleton is achieved directly by the language means.

[ When Ada was designed there was no pattern stuff, which Jeffrey correctly
characterized as workarounds.  Yet Ada designers understood the problem,
maybe unconsciously, and resolved it at the language level. ]

Ada's singleton is an object of anonymous type. Many types allow object
declarations of anonymous types, which guarantees single instance, because
the type has no name.

Array singleton:

   Singleton : array (1..3) of Integer;

Task singleton:

   task Singleton is
      ...
   end task;

Protected object singleton:

   protected Singleton is
      ...
   end task;

Access type singleton (note access, not the target):

   Singleton : [not null] access ...;

For other types the singleton pattern is a declaration of the type and the
instance in the package body. This is probably what Jeffrey meant talking
about packages:

package body P is
   type Nobody_See_Me is ...;
   Singleton : Nobody_See_Me;

P.S. Get_Instance is C++ gibberish because it cannot create/return
unconstrained instances. In Ada you declare an object, singleton or not,
and that creates it. End of story.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de