Re: Ada-Singleton-Why does it work like this?

["patrick.gunia@googlemail.com" <patrick.gunia@googlemail.com>]

On 25 Mrz., 12:10, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:
> On Wed, 25 Mar 2009 03:07:18 -0700 (PDT), patrick.gu...@googlemail.com
> wrote:
>
> > Maybe I´m getting something wrong, but from my point of view,
> > Singleton offers more possibilities than just the execution of some
> > code on elaboration of some module.I like the dynamic version Ludovic
> > described. It also offers the possibility to change the number of
> > instances later on and thus increases the adaptability.
>
> Sorry, but a singleton with more than one instance is not a singleton.

This is arguable. Gamma et al. tell explictily in their work, that it
´s one advantage of the Singleton-pattern that the number of creatable
instances can be fixed later on without major code changes. Thus I
think of the pattern more like a possibility to gain control over the
number of instantiations of a concrete class, not necessarily
restricted to one, though limited.


> > When you say
> > that Singleton isn´t necessary in Ada this might come from the fact
> > that it can´t be implemented as in other languages, though using such
> > a construct might increase readability of the code.
>
> No, it is rather so, that the problems solved in other languages using the
> singleton pattern, in Ada are solved using different patterns.
>
> There is a general note about software design patterns, that they usually
> indicate some language deficiency. If a language has a construct to express
> the idea behind the pattern, then it is not a pattern anymore. Pattern
> assumes some manual, yet routine work on the programmer side, which cannot
> be taken over by the language, because ...

This might be true for some simple patterns like Singleton, though I
think that most patterns solve problems which are language
independent, thus not aiming at a language deficiency. For example
patterns for using frameworks or letting different interfaces
communicate with each other. It seems to me that this is an
architectural question, not a language question.