[GD-Windows] Array foreach in scripting languages

[Carsten O. <car...@se...>]

I'm currently building a small scripting language for interactive stuff. =
Now I
know there's plenty out there, I'm just doing this for fun.
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A tricky question came up and I'd like to collect opinions and =
experiences on
this. It's about foreach for dynamic arrays. Consider this C++-like =
pseudo code:
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DynamicArray<int> list;
int i;
for(i=3D0;i<20;i++){list.Add(i);};
foreach(i in list){
    print(i);
    if(i=3D=3D8){list.Delete(12);};
};
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The obvious question is how should an active iterator react if the =
traversed list
changes? To answer this, I simply tried it out in two languages I know =
that do
provide both dynamic arrays and foreach: STL, Tcl and C#.
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In STL C++ code, I get an exception because of iterator incompatibility.
In Tcl this problem isn't one because the iterator takes a snapshot of =
the list
object on start and there's no language construct to actually change =
this instance.
In C# with the List<int> generic, I get an exception because the =
iterated object
changes (interestingly, this happens on ANY change to the list, even =
appending).
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Now what I'd like to know:
- how do other languages cope with this? (Tcl doesn't need to, C++/C# =
simply fails)
- what do YOU think would be sensible behaviour?
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Currently I'm considering having all iterators be elements of a =
double-linked list
and let the array object be the dl-list head. So if the number of array =
elements
changes, it can run through all attached iterators and fix their indices =
or stop them.
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Carsten Orthbandt
Founder + Development Director
SEK SpieleEntwicklungsKombinat GmbH
http://www.sek-ost.de

Wenn ich Visionen habe, gehe ich zum Arzt. - Helmut Schmidt
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