On Tue, Oct 4, 2016 at 9:37 AM, CodeDmitry <[email protected]> wrote:
> Oh! I see where I got confused now!
>
> "static" variables in Pharo outlive their Playground call!
More than that. They outlive closing the image. The paradigm*** shift
you need to make is that while the lifetime of "static" variables of a
C/C++ program ends when program execution ends, and even though you
stop and start execution of the VM, the execution of the "Image"
*never* ends, it is only suspended.
Try this experiment...
In the System Browser...
Morph subclass: #MyMorph
instanceVariableNames: ''
classVariableNames: ''
package: 'AnExperiment'
MyMorph>>step
self right > Display width ifTrue: [ self left: 0 ].
self left: self left + 10.
MyMorph>>stepTime
^100
In Playground...
(m := MyMorph new) openInWorld.
"After it has been running a while, Save & Quit the image**, then
restart it. Notice the movement of the morph continues from where it
left off."
m delete. "...sometime later"
**Even copy the image and changes to another machine they start it up there.
*** and perhaps you might notice a change in your perception of "what
is possible" from exposure in your course to the "dead" language of
Smalltalk. And further, consider MyMorph is part of a control system
for a nuclear power plant or financial trading system operating 365x24
and you want to change MyMorph from moving right to moving left.
Consider how you would do that in C++ without stopping the system for
even a second, compared to doing that in Pharo. Now Pharo may not be
production ready (i.e. $$$) to run a nuclear power plant, but the
concept of making such "live" changes to compiled code is now a
concept you can carry forward to other disciplines.
cheers -ben
>
> If I call
>
> Greeter greet.
> Greeter greeting: 'Hi!'.
> Greeter greet.
>
> Even if greet sets greeting to an initial value if it is nil, it will
> forever then stay 'Hi!' until I change it or reset it.
>
> So it is not unreasonable to get a response 'Hi! Hi!' in the playground even
> though 'Hi!' only gets set after greet is called, since the global state
> outlives the Transcript!
