Thin delegate adapter

[Dmitry Olshansky]

On 13.01.2011 2:16, Guilherme Vieira wrote:
> No sh*t..?! @__@ That's so cool! But is it smart enough to know the 
> stack frame doesn't need to go to heap in this case? (since it returns 
> a heap object referecing another heap object, i.e. can it untangle `b' 
> from the stack?)

Ehm, it can optimize certain cases but for the moment it doesn't.
Still, it needs to store b somewhere, right? and delegate is 2 pointers 
in fact, so b should go on heap anyway. So it narrows down to if it can 
save only parts of the stack frame ...
>
> -- 
> Atenciosamente / Sincerely,
> Guilherme ("n2liquid") Vieira
>
>
> On Wed, Jan 12, 2011 at 11:49 AM, Dmitry Olshansky 
> <dmitry.olsh at gmail.com <mailto:dmitry.olsh at gmail.com>> wrote:
>
>     On 12.01.2011 16:07, Guilherme Vieira wrote:
>
>         Ah, I totally missed that. But what if `s' went out of the
>         scope and the scope ended? Wouldn't the scope reference (the
>         one containing `b') be lost and cause memory corruption?
>
>         E.g.:
>
>            Switch make_switch()
>            {
>                auto s = new Switch();
>                auto b = new ToggleButton();
>
>                s.watch = (Switch.State state) { b.toggled =
>         cast(bool)(state); };
>
>
>                return s;
>            }
>
>
>     That's the main point of built-in delegates - the compiler detects
>     them and places the enclosing stack frame on heap, so it's all
>     sort of cool magic that just works :)
>
>         -- 
>         Atenciosamente / Sincerely,
>         Guilherme ("n2liquid") Vieira
>
>         On Wed, Jan 12, 2011 at 10:57 AM, Dmitry Olshansky
>         <dmitry.olsh at gmail.com <mailto:dmitry.olsh at gmail.com>
>         <mailto:dmitry.olsh at gmail.com <mailto:dmitry.olsh at gmail.com>>>
>         wrote:
>
>            On 12.01.2011 15:41, Guilherme Vieira wrote:
>
>                Hi,
>
>                I'm wondering if a delegate adapter template like isn't
>         handy
>                for Phobos (it may be especially useful for std.signal):
>
>                   class Switch
>                   {
>                       enum State { ON, OFF }
>
>                       void trigger()
>                       {
>                           switch (mState)
>                           {
>                               case State.ON: mState = State..OFF; break;
>                               case State.OFF: mState = State.ON; break;
>                               default: break;
>                           }
>
>                           if (watch !is null) watch(mState);
>                       }
>
>                       void delegate(State s) watch;
>
>                       private State mState;
>                   }
>
>                   class ToggleButton
>                   {
>                       @property toggled(bool toggled)
>                       {
>                           writeln("ToggleButton.toggled(", toggled, ")");
>                       }
>                   }
>
>                   void main()
>                   {
>                       scope s = new Switch();
>                       scope b = new ToggleButton();
>
>                       s.watch = &b.toggled; // error: invalid conversion
>                       s.watch = adapt!("obj.toggled = cast(bool)(a)",
>                Switch.State)(b);
>
>                       s.trigger(); // prints `ToggleButton.toggled(true)`
>                       s.trigger(); // prints `ToggleButton.toggled(false)`
>                       s.trigger(); // prints `ToggleButton.toggled(true)`
>                       s.trigger(); // prints `ToggleButton.toggled(false)`
>                   }
>
>
>                Yes, it urges to be polished. Particularly, it doesn't
>         support
>                multiple arguments. I also wanted to place the argument
>         type
>                tuple somwhere else (actually wanted to hide it completely,
>                but I think that's not possible).
>
>                Feedback?
>
>                --         Atenciosamente / Sincerely,
>                Guilherme ("n2liquid") Vieira
>
>            How is it better then built-in language feature? This works
>         just fine:
>               void main()
>               {
>            //they can't be scope  and compiler enforces this (+ scope is
>            deprecated)
>            //actually, the orignal code is unsafe - what hapens if adapted
>            delegate escapes current scope?
>                   auto s = new Switch();
>                   auto b = new ToggleButton();
>
>
>                   s.watch = (Switch.State a){ b.toggled = cast(bool)a; };
>
>                   s.trigger(); // prints `ToggleButton.toggled(true)`
>                   s.trigger(); // prints `ToggleButton.toggled(false)`
>                   s.trigger(); // prints `ToggleButton.toggled(true)`
>                   s.trigger(); // prints `ToggleButton.toggled(false)`
>               }
>
>            --     Dmitry Olshansky
>
>
>
>     -- 
>     Dmitry Olshansky
>


-- 
Dmitry Olshansky