Singleton Pattern with struct

[Maxim Fomin]

On Thursday, 24 January 2013 at 17:00:44 UTC, Ali Çehreli wrote:
> On 01/24/2013 08:52 AM, ParticlePeter wrote:
>
> > This method here ( my first approach ) does return a
> reference to an
> > object on the heap, right ?
>
> Yes, but the caller does not get a reference.

Actually the caller gets the reference (which is a pointer from 
low-level POV), but allocates on stack struct object, and then 
does copy from returned reference to that stack object.

> > 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 ?
>
> When you print the type of another_s you will see that it is 
> not a ref, because unlike C++, D does not have local ref 
> variables; it has pointers for that purpose.
>

Yes, that the point - D does not have references like C++. And I 
should thought about C++ influence on understanding D :)

> import std.stdio;
>
> ref int foo()
> {
>     return *new int;
> }
>
> void main()
> {
>     auto i = foo();
>     writeln(typeid(i));
> }
>
> Prints 'int', not 'ref int'. So, i is a copy of the dynamically 
> created int.
>
> Ali