Re: Singleton Pattern with struct

[ParticlePeter]

Yes, but this can be broken by:

import core.stdc.stdio : printf;
struct Singleton  {

private :
        this( int a = 0 ) {} ;
        static Singleton * s ;

public :
        @disable this() ;
        static Singleton* instance()  {
                if ( s is null )
                        s = new Singleton(0) ;
                return s ;
        }

        int val = 0 ;
}

void main()
{
        Singleton s = * Singleton.instance;
        printf( "%d\n", s.val ) ; //
        Singleton.instance.val = 2 ;
        printf( "%d\n", s.val ) ; //0
}

Here s is explicitly defined to be a struct object, not pointer 
(reference), so main.s is independent of further modification 
of Singleton.instance.

O.k. good to know, I'll try to avoid this. But one thing is still 
not clear,
This method here ( my first approach ) does return a reference to 
an object on the heap, right ?

static ref Singleton instance()  {
        if ( s is null )
                s = new Singleton( 0 ) ;
        return * s ;
}

so when I use it with:
auto another_s = Singleton.instance ;

Why is the s inside the struct and another_s not identical ?
Afaik that is the purpose of the ref keyword ?