Singleton Pattern with struct

[Artur Skawina]

On 01/24/13 18:35, ParticlePeter wrote:
> On Thursday, 24 January 2013 at 17:21:38 UTC, Artur Skawina wrote:
>> On 01/24/13 17:52, ParticlePeter wrote:
>>> Why is the s inside the struct and another_s not identical ?
>>> Afaik that is the purpose of the ref keyword ?
>>
>> There currently are no reference variables in D [1]; the only way to get
>> a reference to something is via function arguments (including implicit
>> method ones) and function returns. So assigning a ref-return means a copy.
>>
>> You can workaround it like this:
>>
>> struct Singleton  {
>> private:
>>     this( int a = 0 ) {} ;
>>     static Singleton* s ;
>>
>> public:
>>     @disable this();
>>     @disable this(this);
>>     static instance() @property {
>>         static struct Ref(T) { T* obj; ref g() @property { return *obj; } alias g this; @disable this(this); }
>>         if ( s is null )
>>             s = new Singleton( 0 ) ;
>>         return Ref!(typeof(this))(s) ;
>>     }
>>
>>     int val = 0 ;
>> }

> Well ... I think I as well would not wanna do it like this, thanks :-)
> I'm fine with returning and using a pointer, fortunately there is no difference in syntax as in c, so it doesn't matter.

Careful, at some point you'll end up doing s[1] etc, and /then/ it matters.
The Ref struct is actually the way to deal with "ref" types in D; what I meant
by 'that's not how I'd do it' is that it might be better to use a global
(well, thread-local module-field in D) etc.

artur