Thin delegate adapter

[Guilherme Vieira]

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?)

-- 
Atenciosamente / Sincerely,
Guilherme ("n2liquid") Vieira


On Wed, Jan 12, 2011 at 11:49 AM, Dmitry Olshansky <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>> 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
>
>
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