Do I have a THread-safe singleton ? If not HowTo..   Sorry. Sean K allready explains it to me, but I 've lost the info. :(
Bjoern

class Singleton(T)
{
  public:
  static T instance()
  sychronized       // according to the language spec this should work
  {
    if(_instance is null) _instance = new T;
    return _instance;
  }

  private:
  this() {}

  static T _instance;
}

class Application : Singleton!(Application)
{
}

Reply to bls,

> Do I have a THread-safe singleton ? If not HowTo..   Sorry. Sean K
> allready explains it to me, but I 've lost the info. :(
> Bjoern
> class Singleton(T)
> {
> public:
> static T instance()
> sychronized       // according to the language spec this should
> work
> {
> if(_instance is null) _instance = new T;
> return _instance;
> }
> private:
> this() {}
> static T _instance;
> }
> class Application : Singleton!(Application)
> {
> }

I think this will fail because Singleton!(Application).instance() will call Application's this() and that is private.

IMHO, a better approach (that I haven't tested) would be to use a mixin:

template Singleton(T)
{
 public:
 static T instance() sychronized
      // according to the language spec this should work
 {
   if(_instance is null) _instance = new T;
   return _instance;
 }
 private:
 this() {}
 static T _instance;
}

class Application : Singleton!(Application)
{
 mixin(Singleton!(typeof(this)));
}

BCS schrieb:
> Reply to bls,
> 
>> Do I have a THread-safe singleton ? If not HowTo..   Sorry. Sean K
>> allready explains it to me, but I 've lost the info. :(
>> Bjoern
>> class Singleton(T)
>> {
>> public:
>> static T instance()
>> sychronized       // according to the language spec this should
>> work
>> {
>> if(_instance is null) _instance = new T;
>> return _instance;
>> }
>> private:
>> this() {}
>> static T _instance;
>> }
>> class Application : Singleton!(Application)
>> {
>> }
> 
> I think this will fail because Singleton!(Application).instance() will call Application's this() and that is private.
> 
> IMHO, a better approach (that I haven't tested) would be to use a mixin:
> 
> template Singleton(T)
> {
>  public:
>  static T instance() sychronized
>       // according to the language spec this should work
>  {
>    if(_instance is null) _instance = new T;
>    return _instance;
>  }
>  private:
>  this() {}
>  static T _instance;
> }
> 
> class Application : Singleton!(Application)
> {
>  mixin(Singleton!(typeof(this)));
> }
> 
> 

Thanks BCS,

Confused  ...'cause virus infected (me) not the pc


class Application : Singleton!(Application)
{
  mixin(Singleton!(typeof(this)));
  this()
  {
    return instance(this)
  }
}

Honk, that stinks somehow !

Hope I ask not for too much, but please explain the use of the mixin
Bjoern

Reply to bls,

> BCS schrieb:
> 
>> Reply to bls,
>> 
>>> Do I have a THread-safe singleton ? If not HowTo..   Sorry. Sean K
>>> allready explains it to me, but I 've lost the info. :(
>>> Bjoern
>>> class Singleton(T)
>>> {
>>> public:
>>> static T instance()
>>> sychronized       // according to the language spec this should
>>> work
>>> {
>>> if(_instance is null) _instance = new T;
>>> return _instance;
>>> }
>>> private:
>>> this() {}
>>> static T _instance;
>>> }
>>> class Application : Singleton!(Application)
>>> {
>>> }
>> I think this will fail because Singleton!(Application).instance()
>> will call Application's this() and that is private.
>> 
>> IMHO, a better approach (that I haven't tested) would be to use a
>> mixin:
>> 
>> template Singleton(T)
>> {
>> public:
>> static T instance() sychronized
>> // according to the language spec this should work
>> {
>> if(_instance is null) _instance = new T;
>> return _instance;
>> }
>> private:
>> this() {}
>> static T _instance;
>> }
>> class Application : Singleton!(Application)
>> {
>> mixin(Singleton!(typeof(this)));
>> }
> Thanks BCS,
> 
> Confused  ...'cause virus infected (me) not the pc
> 
> class Application : Singleton!(Application)
> {
> mixin(Singleton!(typeof(this)));
> this()
> {
> return instance(this)
> }
> }
> Honk, that stinks somehow !
> 

Oops, typo!!

class Application // no ": ..."

> Hope I ask not for too much, but please explain the use of the mixin

Think of a mixin as a copy/paste + macro. Instance the template (that's the macro part) and just lump it into whatever scope you use it in (the copy/paste part). It's a quick way to do boiler plate coding.

> Bjoern
> 

BCS schrieb:
> Reply to bls,
> 
>> BCS schrieb:
>>
>>> Reply to bls,
>>>
>>>> Do I have a THread-safe singleton ? If not HowTo..   Sorry. Sean K
>>>> allready explains it to me, but I 've lost the info. :(
>>>> Bjoern
>>>> class Singleton(T)
>>>> {
>>>> public:
>>>> static T instance()
>>>> sychronized       // according to the language spec this should
>>>> work
>>>> {
>>>> if(_instance is null) _instance = new T;
>>>> return _instance;
>>>> }
>>>> private:
>>>> this() {}
>>>> static T _instance;
>>>> }
>>>> class Application : Singleton!(Application)
>>>> {
>>>> }
>>> I think this will fail because Singleton!(Application).instance()
>>> will call Application's this() and that is private.
>>>
>>> IMHO, a better approach (that I haven't tested) would be to use a
>>> mixin:
>>>
>>> template Singleton(T)
>>> {
>>> public:
>>> static T instance() sychronized
>>> // according to the language spec this should work
>>> {
>>> if(_instance is null) _instance = new T;
>>> return _instance;
>>> }
>>> private:
>>> this() {}
>>> static T _instance;
>>> }
>>> class Application : Singleton!(Application)
>>> {
>>> mixin(Singleton!(typeof(this)));
>>> }
>> Thanks BCS,
>>
>> Confused  ...'cause virus infected (me) not the pc
>>
>> class Application : Singleton!(Application)
>> {
>> mixin(Singleton!(typeof(this)));
>> this()
>> {
>> return instance(this)
>> }
>> }
>> Honk, that stinks somehow !
>>
> 
> Oops, typo!!
> 
> class Application // no ": ..."
> 
>> Hope I ask not for too much, but please explain the use of the mixin
> 
> Think of a mixin as a copy/paste + macro. Instance the template (that's the macro part) and just lump it into whatever scope you use it in (the copy/paste part). It's a quick way to do boiler plate coding.
> 
>> Bjoern
>>
> 
> 
Thanks BCS:
>>>>> class Application // no ": ..."

Ah, that makes more sense :)

Okay .
Now; to make it smart .

class Application
{
  class Singleton
  {
  }
}
You mean ... shi. ?

very very big grin
Seriously? I need a bullet proof thread safe singleton implementation ..

Hell I should change my BLS into LS , people here are sometimes confused.
Bjoern

Reply to bls,
>>> BCS schrieb:
>>>>
>>>> template Singleton(T)
>>>> {
>>>> public:
>>>> static T instance() sychronized
>>>> // according to the language spec this should work
>>>> {
>>>> if(_instance is null) _instance = new T;
>>>> return _instance;
>>>> }
>>>> private:
>>>> this() {}
>>>> static T _instance;
>>>> }
>>>> class Application : Singleton!(Application)
>>>> {
>>>> mixin(Singleton!(typeof(this)));
>>>> }

> 
> class Application // no ": ..."
> 
> Ah, that makes more sense :)
> 
> Okay .
> Now; to make it smart .
> class Application
> {
> class Singleton
> {
> }
> }
> You mean ... shi. ?
> 

Almost. It might not be important, but because Singleton is a template rather than a templated class, the inner class you show doesn't exist.

You more or less end up getting this:

class Application
{
 public:
 static Application instance() sychronized
 // according to the language spec this should work
 {
  if(_instance is null) _instance = new Application;
  return _instance;
 }
 private:
 this() {}
 static Application _instance;
}

BCS schrieb:
> Reply to bls,
>>>> BCS schrieb:
>>>>>
>>>>> template Singleton(T)
>>>>> {
>>>>> public:
>>>>> static T instance() sychronized
>>>>> // according to the language spec this should work
>>>>> {
>>>>> if(_instance is null) _instance = new T;
>>>>> return _instance;
>>>>> }
>>>>> private:
>>>>> this() {}
>>>>> static T _instance;
>>>>> }
>>>>> class Application : Singleton!(Application)
>>>>> {
>>>>> mixin(Singleton!(typeof(this)));
>>>>> }
> 
>>
>> class Application // no ": ..."
>>
>> Ah, that makes more sense :)
>>
>> Okay .
>> Now; to make it smart .
>> class Application
>> {
>> class Singleton
>> {
>> }
>> }
>> You mean ... shi. ?
>>
> 
> Almost. It might not be important, but because Singleton is a template rather than a templated class, the inner class you show doesn't exist.
> 
> You more or less end up getting this:
> 
> class Application
> {
>  public:
>  static Application instance() sychronized
>  // according to the language spec this should work
>  {
>   if(_instance is null) _instance = new Application;
>   return _instance;
>  }
>  private:
>  this() {}
>  static Application _instance;
> }
> 
> 
Okay, I see.
Last question,(promised) As far as I can remember Sean and I talked about to use volatile ...
here it is
http://www.digitalmars.com/d/archives/digitalmars/D/Threadsafe_singleton_using_volatile_synchonized_53768.html

What do you think ?
Bjoern

Reply to bls,

> Okay, I see.
> 
> Last question,(promised) As far as I can remember Sean and I talked
> 
> about to use volatile ...
> 
> here it is
> 
> http://www.digitalmars.com/d/archives/digitalmars/D/Threadsafe_singlet
> on_using_volatile_synchonized_53768.html
> 
> What do you think ?
> Bjoern

Thread safety isn't my thing, sorry.

BCS schrieb:
> Reply to bls,
> 
>> Okay, I see.
>>
>> Last question,(promised) As far as I can remember Sean and I talked
>>
>> about to use volatile ...
>>
>> here it is
>>
>> http://www.digitalmars.com/d/archives/digitalmars/D/Threadsafe_singlet
>> on_using_volatile_synchonized_53768.html
>>
>> What do you think ?
>> Bjoern
> 
> Thread safety isn't my thing, sorry.
> 
> 
Anyway, thanks for spending your time :)

BLS schrieb:
> Do I have a THread-safe singleton ? If not HowTo..   Sorry. Sean K allready explains it to me, but I 've lost the info. :(
> Bjoern
> 
> class Singleton(T)
> {
>   public:
>   static T instance()
>   sychronized       // according to the language spec this should work
>   {
>     if(_instance is null) _instance = new T;
>     return _instance;
>   }
> 
>   private:
>   this() {}
> 
>   static T _instance;
> }
> 
> class Application : Singleton!(Application)
> {
> }

Okay, I'll have to think more about this stuff.
In case that somebody can offer a templated (thread-safe and bulletproof) Singleton class. ... THANKS
Bjoern