Imagine I have a very short-lived class:

void print(File f)
{
    PrinterManager pm = new PrinterManager();
    pm.print(f);
}

My understanding is that PrinterManager will be GC allocated, and when it goes out of scope, the GC will possibly clean it up at some point in the future. But I know that this class won't be used anywhere, I want to clean it up right now so that GC doesn't waste time later. In C++ it'd be handled by RAII, pm would be a unique_ptr<PrinterManager>. How to do it in D?

On Wednesday, 4 July 2018 at 15:47:25 UTC, JN wrote:
> Imagine I have a very short-lived class:
>
> void print(File f)
> {
>     PrinterManager pm = new PrinterManager();
>     pm.print(f);
> }
>
> My understanding is that PrinterManager will be GC allocated, and when it goes out of scope, the GC will possibly clean it up at some point in the future. But I know that this class won't be used anywhere, I want to clean it up right now so that GC doesn't waste time later. In C++ it'd be handled by RAII, pm would be a unique_ptr<PrinterManager>. How to do it in D?

https://dlang.org/phobos/std_typecons.html#scoped

On Wednesday, July 04, 2018 15:47:25 JN via Digitalmars-d-learn wrote:
> Imagine I have a very short-lived class:
>
> void print(File f)
> {
>      PrinterManager pm = new PrinterManager();
>      pm.print(f);
> }
>
> My understanding is that PrinterManager will be GC allocated, and when it goes out of scope, the GC will possibly clean it up at some point in the future. But I know that this class won't be used anywhere, I want to clean it up right now so that GC doesn't waste time later. In C++ it'd be handled by RAII, pm would be a unique_ptr<PrinterManager>. How to do it in D?

The typical thing to do in that case is to use a struct, not a class, since structs have RAII, and they don't need to be allocated on the heap. However, if you're stuck with a class, you can use scope. e.g.

scope pm = new PrintManager;

In that case, the class will actually be allocated on the stack instead. However, I would point out that until -dip1000 becomes the normal behavior, using scope like this is unsafe, because you have serious problems if any reference to the class object escapes, since it's stack-allocated instead of heap-allocated, and if any reference to it escapes, then it's referring to an invalid object. If you're careful, it's fine, but it is a risk, and regardless, using a struct is preferable if it's possible.

-dip1000 fully implements scope so that it verifies that no reference escapes, but it's not ready yet, let alone the default behavior.

- Jonathan M Davis

On Wednesday, 4 July 2018 at 16:02:25 UTC, Jonathan M Davis wrote:
> -dip1000 fully implements scope so that it verifies that no reference escapes, but it's not ready yet, let alone the default behavior.
>
> - Jonathan M Davis

I read the proposal about -dip1000 ( not all, some ) and there is also a scoped! template in std.typecons, so...is it better to use the scope keyword, or scoped! template

On Thursday, July 05, 2018 05:47:20 Flaze07 via Digitalmars-d-learn wrote:
> On Wednesday, 4 July 2018 at 16:02:25 UTC, Jonathan M Davis wrote:
> > -dip1000 fully implements scope so that it verifies that no reference escapes, but it's not ready yet, let alone the default behavior.
> >
> > - Jonathan M Davis
>
> I read the proposal about -dip1000 ( not all, some ) and there is also a scoped! template in std.typecons, so...is it better to use the scope keyword, or scoped! template

Long term, it will be better to use the scope keyword. Short term (i.e. until -dip1000 is the normal behavior or at least ready to use), it may be better to use scoped, since I think that the wrapper protects you at least somewhat - though the main reason that it was originally introduced is that scope on classes was going to deprecated, because we didn't want something that unsafe to be a keyword, but DIP 1000 is changing that.

- Jonathan M Davis