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D - Singleton class or struct: how to?

reply "Kris" <someidiot earthlink.net> writes:
What is the best way in D to declare a singleton? Currently I use:

// the singleton type
class Bar
{
    void func();
}

// the singleton instance
struct Foo
{
   static Bar bar;

   static this()
   {
   bar = new Bar();
   }
}

// usage
void test()
{
    Foo.bar.func();
}

However, a user can happily instantiate additional instances of the
singleton simply by

void test()
{
    Foo myFoo;
}

which is not cool. Also, a user can {Foo.bar = null;} since bar is not
const. I tried using the 'final' keyword, but that doesn't appear to have an
effect.

Ideas? Comments?

- Kris
Mar 26 2004
next sibling parent reply "Matthew" <matthew stlsoft.org> writes:
Just make the ctor private.

But I tend to agree with other commentators on this NG on this subject,
which is that D's module functionality - which, btw, is deterministic,
unlike that of C++ - renders the representation of singletons as objects
rather jejune. :-)


"Kris" <someidiot earthlink.net> wrote in message
news:c420o8$65e$1 digitaldaemon.com...

 What is the best way in D to declare a singleton? Currently I use:

 // the singleton type
 class Bar
 {
     void func();
 }

 // the singleton instance
 struct Foo
 {
    static Bar bar;

    static this()
    {
    bar = new Bar();
    }
 }

 // usage
 void test()
 {
     Foo.bar.func();
 }

 However, a user can happily instantiate additional instances of the
 singleton simply by

 void test()
 {
     Foo myFoo;
 }

 which is not cool. Also, a user can {Foo.bar = null;} since bar is not
 const. I tried using the 'final' keyword, but that doesn't appear to have


an

 effect.

 Ideas? Comments?

 - Kris
Mar 26 2004
parent reply "Kris" <someidiot earthlink.net> writes:
"Matthew" <matthew stlsoft.org> wrote in message
news:c422t8$9ji$1 digitaldaemon.com...

 Just make the ctor private.


Did you mean this Matthew?

class Foo
{
    private this(){}
}

the private attribute is thoroughly ignored by the compiler ...

BTW, I searched (via Outlook) for other threads on Singleton, but didn't
find anything. Is there someplace to search the "older" threads?
(digitalmars/d/index does not support search).

Thanks;
Mar 26 2004
next sibling parent reply Manfred Nowak <svv1999 hotmail.com> writes:
On Fri, 26 Mar 2004 12:49:56 -0800, Kris wrote:

[...]

 BTW, I searched (via Outlook) for other threads on Singleton, but didn't
 find anything.


http://www.digitalmars.com/drn-bin/wwwnews?D/21642
==
<bu0da8$1qic$1 digitaldaemon.com>

So long!
Mar 26 2004
parent "Kris" <someidiot earthlink.dot.dot.dot.net> writes:
Cheers Manfred!


"Manfred Nowak" <svv1999 hotmail.com> wrote in message
news:c42omb$1bhu$1 digitaldaemon.com...

 On Fri, 26 Mar 2004 12:49:56 -0800, Kris wrote:

 [...]

 BTW, I searched (via Outlook) for other threads on Singleton, but didn't
 find anything.


 http://www.digitalmars.com/drn-bin/wwwnews?D/21642
 ==
 <bu0da8$1qic$1 digitaldaemon.com>

 So long!
Mar 26 2004
prev sibling parent reply "Matthew" <matthew stlsoft.org> writes:
"Kris" <someidiot earthlink.net> wrote in message
news:c424kb$c4f$1 digitaldaemon.com...

 "Matthew" <matthew stlsoft.org> wrote in message
 news:c422t8$9ji$1 digitaldaemon.com...

 Just make the ctor private.


 Did you mean this Matthew?

 class Foo
 {
     private this(){}
 }


Yep.


 the private attribute is thoroughly ignored by the compiler ...


It sounds flippant, but I wouldn't worry about it. You shouldn't get
confused between a language feature and a compiler bug, which will likely be
fixed in the next release (as most do).
Mar 30 2004
parent "Kris" <someidiot earthlink.dot.dot.dot.net> writes:
Thanks.

"Matthew" <matthew stlsoft.org> wrote in message
news:c4dkp1$8hh$3 digitaldaemon.com...

 "Kris" <someidiot earthlink.net> wrote in message
 news:c424kb$c4f$1 digitaldaemon.com...

 "Matthew" <matthew stlsoft.org> wrote in message
 news:c422t8$9ji$1 digitaldaemon.com...

 Just make the ctor private.


 Did you mean this Matthew?

 class Foo
 {
     private this(){}
 }


 Yep.


 the private attribute is thoroughly ignored by the compiler ...


 It sounds flippant, but I wouldn't worry about it. You shouldn't get
 confused between a language feature and a compiler bug, which will likely


be

 fixed in the next release (as most do).
Mar 31 2004
prev sibling parent reply Stephan Wienczny <wienczny web.de> writes:
Kris wrote:

 
 Ideas? Comments?
 
 - Kris
 
 


Use a module:

//Your singleton
module bar;

void func()
{

}

usage:

module xyz;

void another_func()
{
	bar.func();
}

Stephan
Mar 26 2004
parent reply "Kris" <someidiot earthlink.net> writes:
Cool. Thanks Stephan.

In this particular case, I'd really like to keep the extended namespace
intact, as in Foo.bar.func().  Is that possible using the module-technique?

- Kris


"Stephan Wienczny" <wienczny web.de> wrote in message
news:c42345$9uo$1 digitaldaemon.com...

 Kris wrote:

 Ideas? Comments?

 - Kris


 Use a module:

 //Your singleton
 module bar;

 void func()
 {

 }

 usage:

 module xyz;

 void another_func()
 {
 bar.func();
 }

 Stephan
Mar 26 2004
parent J Anderson <REMOVEanderson badmama.com.au> writes:
Kris wrote:


Cool. Thanks Stephan.

In this particular case, I'd really like to keep the extended namespace
intact, as in Foo.bar.func().  Is that possible using the module-technique?

- Kris
  


Surround it in structs and make everything static.

-- 
-Anderson: http://badmama.com.au/~anderson/
Mar 26 2004