Re: Properties

[Maciej Sobczak <see.my.homepage@gmail.com>]

On Dec 2, 4:46 pm, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:

> > Safe? What is the benefit of safe if at the same time it's pointless?
>
> > Put ("My ");
> > Put ("name ");
> > Put ("is ");
> > Put_Line ("Maciej");
>
> > I have multiple tasks doing it. What is safe for you?
>
> 1. It does not crash, the effect is defined
> 2. Put is atomic

These are very weak requirements. The information was scrambled - the
mail packages arrived at the wrong address, the missile attacked the
wrong country and the doctor removed the liver of the wrong patient.
But nothing crashed. :-)

The reasons why it's pointless to internally synchronize GUI (or
Text_IO) are exactly the same as why it's pointless to synchronize
standard containers. It's the wrong level of granularity. You might
steer away from erroneous execution, but that does not in itself make
the program correct.

> >> GUI is natively multitasking:
>
> >> 1. actions invoked by its controls are not instant: progress bar
> >> 2. some controls are active objects: animation widgets, visual effects,
> >> tooltips, hovering etc
> >> 3. indication of asynchronous events and data: oscilloscope
>
> > How is that any different from standard output?
>
> What is different/same from what?

GUI from Text_IO.

I will try to answer myself: the difference is that Text_IO, as an
abstract stream, "feels" sequential by nature, whereas GUI, with its
2D layout (+ time dimension for content changes), makes concurrency
more appealing. Still, good design principles call for decoupling of
application logic and display (maybe with some intermediate "data
model" module?) and this decoupling blurs that distinction
significantly.

I'm not convinced that GUI should be task-safe. Supporting bad
application designs would be a wrong justification.

--
Maciej Sobczak * http://www.inspirel.com