[etoys-dev] duplicates and siblings

Rita Freudenberg rita at isg.cs.uni-magdeburg.de
Thu Feb 24 10:32:57 EST 2011

Thanks for all your answers! The quick guides are great! Steve, thank you very much for pointing me to the chapter about siblings, this really got lost when I imported the manual to the new booki-system. Now I'll look at the old site more carefully to find what else I might have missed. Fortunately, it is not lost yet. 
Derek, I agree that it is a good idea to orientate ourselfs on existing software terminology. For the manual, we need to use the terms we find in Etoys. But terms can be discussed and changed in later versions, if we have a good reason. 

Here is the new link to the reference manual. Please help us review the "Getting Started" and "User Interface" chapters!


On Feb 23, 2011, at 4:32 PM, Steve Thomas wrote:

> There is a chapter (on hold in the manual that discusses siblings, thanks to Karl for adding this) excerpts from that re-written below.
> When you make a copy of an object any changes made to the copy or the original only affect the object changed. 
> Siblings are related in that they share certain things in common, in particular: scripts and variable definitions.  So if you add a variable to one sibling, all siblings will have their own instance of that variable with the same name. The same name, but the values can be different. For example if I add a variable called "speed" to one sibling, all siblings will have a variable with that name. But I can have one sibling with speed=5 and another with speed=10. Same variable name different values.
> Also if I add a script to one sibling, all siblings will have the same script (and same scripting tiles, if I change it in any sibling at anytime). But although siblings share a script, each sibling has its own private "status" for that script, i.e. remembers separately whether the script as used by this instance is "normal", "paused,", or "ticking", or set to trigger on mouse-up, etc.; and what the tick-rate is. 
> So why would you use siblings? Well besides teaching one of the most fundamental concepts of object oriented programming, you could use siblings in a game to make characters that have similar behaviors (aka scripts) but different looks (you can change the looks by either re-drawing the sketch or by setting the Sketch's graphic (if the object is a Sketch or image you copied in) or changing its size and colors.  You could also have ships in a game that keep track of how many times they were hit (using a variable to count the # of hits). That way you can program a basic ship once and make multiple siblings. Then if you decide to change the behavior (ex: modify a script, or add a new variable), you can change it once and all the siblings are changed. 
> Siblings could also be used to try to simulate or model real world behavior.  For example deer population or some other animal.  You could create an Object that simulates the behavior of a deer: searches for food, ages, breeds (at a certain age), etc. and make sibling copies of that one object. Then each Sibling (aka individual instance of the Class Deer which you have defined) could age, search for food (and find it or not which could affect its life expectancy), etc at its own rate.  You could also create predators and food that grows. Then run multiple simulations varying the amount of food, starting number of dear, # of predators, etc. 
> If the "all instances" box is not checked in AllPlayers, you'll see the scripts for only one player of each sibling group. This will give you "control" over the scripts of only one of the players. If you want to be able to "control" scripts for both of the siblings, make sure the "all 
> instances" checkbox is checked.
> On Wed, Feb 23, 2011 at 9:36 AM, Rita Freudenberg <rita at isg.cs.uni-magdeburg.de> wrote:
> Hi,
> I'm working on the Etoys reference manual right now, and on one place I want to describe the difference between sibling and duplicate. I hope someone here can help me. Here is what I wrote, is this correct? (the green double boxes refer to the green halo icon).
> ------------------
> The green double boxes in the top right duplicates the object. If you hold down the shift key you will create a sibling object. There is a difference between siblings and duplicates. At the moment of creation, it is the same, you will get a copy of the object and all it's scripts. But if you later change an existing script of the original object, the same script of the siblings will change automatically, too. The same script of the duplicates will stay the same as of the moment of the duplication.
> Thanks,
> Rita
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