Re: Singleton

On May 24, 8:13 pm, VK <schools_r...@[EMAIL PROTECTED]
> wrote:
> On May 24, 7:58 pm, Ugo <priv...@[EMAIL PROTECTED]
> wrote:
>
>
>
> > >>> The best way of doing something depends at least in part on what
it is
> > >>> you are trying to do.
> > >> A generic way to create a singleton object
> > > I doubt that is what Richard meant by "what it is you are trying to
> > > do". You are more likely trying to "implement a tabbed pane widget"
or
> > > "send user data to the server". Unless this is just an academic
> > > exercise.
>
> > all this things  :P
>
> > > A generic way to create a singleton object with global access is to
> > > use a object literal.
>
> > > var someSingleton = {
> > >   someProperty: function() {},
> > >   someOtherProperty: 55
> > > };
>
> > But, in this way I can not to declare "private" variables/methods in
an
> > elegant way:
>
> > I don't like it:
>
> > var singleton;
>
> > (function()
> > {
> >         // "privare" prop
> >         var a = 1;
> >         // "private" method
> >         function b( )
> >         {
> >                 alert('hi');
> >         }
>
> >         // Obj
> >         singleton = {
> >                 hi : b,
> >                 a: a
> >         };
>
> > })();
>
> The way I'm using most often - without any claims that it is the best
> out of anything:
>
> function MySingleton() {
>  if (this == self) {
>   window.alert('Conctructor called as a function');
>   return MySingleton;
>  }
>  else if (
>  !!($isInstantiated.flag) ||
>  (this instanceof MySingleton) ||
>  (MySingleton.isPrototypeOf(this))
>  ) {
>   window.alert('Only one instance is allowed');
>   return mySingleton;
>  }
>  else {
>   // instantiate your singleton
>   // with methods and properties
>   // ...
>   this.toString = $toString;
>   $isInstantiated.flag = true;
>  }
>  function $isInstantiated() {
>   return arguments.callee.flag;
>  }
>  function $toString() {
>   return ''.concat(
>    'function mySingleton() {\n',
>    '    [native code]\n',
>    '}'
>   );
>  }
>
> }
>
> The benefits as I see them:
> 1) It is much lesser convoluted as function expression ways.
> Respectively it is easier to read, to maintain and to avoid parasite
> closures.
> 2) It allows to distinct different "not allowed" situation so to
> provide more informative errors - in a real case window.alert replaced
> by throw new Error of course.
> 3) it prevents or at least makes much harder to use reliably runtime
> cloning over source code dumping and reusing in eval or new Function.

A few errors made while pulling out the code and readjusting for
posting, sorry. The corrected version would be:

function MySingleton() {
 if (this == self) {
  window.alert('Conctructor called as a function');
  return MySingleton;
 }
 else if (
 !!($isInstantiated.flag) &&
 ((this instanceof MySingleton) ||
 (MySingleton.isPrototypeOf(this)))
 ) {
  window.alert('Only one instance is allowed');
  return MySingleton;
 }
 else {
  // instantiate your singleton
  // with methods and properties
  // ...
  this.toString = $toString;
  $isInstantiated.flag = true;
 }
 function $isInstantiated() {
  return arguments.callee.flag;
 }
 function $toString() {
  return ''.concat(
   'function mySingleton() {\n',
   '    [native code]\n',
   '}'
  );
 }
}