Add list option tag and getSelection

[andre2007]

Idea is, you can store arbitrary data (e.g. a class pointer) with the item. Therefore while reacting on ChangeEvent, you have all needed data.

import arsd.minigui;

class Foo
{
    int i;
}

void main()
{
    auto window = new MainWindow();
    auto list = new ListWidget(window);

    Foo foo1 = new Foo();
    foo1.i = 3;

    list.addOption("Sample", cast(ptrdiff_t) cast(void*) foo1);

    Foo foo2 = cast(Foo) cast(void*) list.options[0].tag;
    window.loop();
}

[adamdruppe]

OK, yeah, I like it. That's useful. My own concern is typing it as ptrdiff_t but storing pointers in it is technically prohibited by the GC rules; the gc might not see it and prematurely free the reference. Could of course just say that's the user's problem... but I might change that.

Gotta run i'll think about this more and probably merge it later tonight or tomorrow, just keep in mind if I change it before tagging the release you might need to adjust your code too..

[andre2007]

You are right, the sample coding has this bug. The idea is, in some cases it is sufficient to store just a number which might point to a index of another array. In more sophisticated cases you want to store a object refence. Ptrdiff_t can handle both cases.

Another option would be to have multiple tag fields:

Ptrdiff_t tag
Object tagObject
string tagString

[adamdruppe]

Yeah, could be a fancy union or something too. I think the void* is a reasonable type for the low level then maybe a template interface on top could do better.

[adamdruppe]

I just tagged a thing but haven't had time to work back on this yet, I'll get there eventually though. I have a couple projects with a Thursday deadline so hopefully my time will open up again by then. I probably do have a plan here though.

[adamdruppe]

Well, I'm finally out of the deadline crunch, the stuff that isn't done we're just living without. So got a bit of time here.

Going with just this little change to your PR for now: https://github.com/adamdruppe/arsd/commit/e36512f1d487c9c7fbc6a97842f922aff186f79c

and we'll see about a nicer api in a bit, like adding a runtime type check or something. Just didn't want to keep you waiting another eternity.

[andre2007]

Thank you Adam.