Double Entry in AILists

[Hephi]

Hi, I'm having a strange problem with AIAbstractLists

for example

local townList = AITownList();
AILog.Info("b="+townList.Begin());
while(townList.HasNext()){
AILog.Info("t="+townList.Next());
}

would return this (say there are 3 towns on the map)

b= 2
t= 1
t= 0
t= 0

As you can see the last town on the list is shown twice.
If you would sort the list it will give for example

b= 0
t= 2
t= 1
t= 1

I tried fixing this by adding townList.RemoveLast(1) before
doing the loop but then it shows like (taken last sorted example)

b= 0
t= 2
t= 2

Correctly removing the last town (1) but again repeating the last item in the list twice

So, the initial list is correct but somehow the loop iterates the last item twice.
The last call to HasNext() should return false but doesn't.
Strangely enough it does return false the time after that (otherwise it would loop infinitely)


Can someone explain to me what's happening here?
Should I give up on while-loops and use for-loops instead?

edit: using 0.7.3 on win vista

[Zutty]

Hmmm... I cant explain whats going wrong, but I would suggest that you use a foreach loop instead...

Code: Select all

foreach(townId, _ in AITownList()) {
  AILog.Info("t="+townId);
}

Note that the _ is just a dummy variable. The foreach loop takes as parameters either (value in list) or (key, value in list). If you only wanted the values then you could omit the key (though you cant omit the value and only get the key). For example...

Code: Select all

local total = 0, towns = AITownList();
towns.Valuate(AITown.GetPopulation);
foreach(population in towns) total += population;
AILog.Info("Total world population is "+total);

Hope this helps.

[Zuu]

That is awesome! Didn't knew you could use the foreach loop for AI*List. I have been using it only for Squirrel arrays. The foreach loop saves so much typing that could go wrong.

[Blustuff]

You can use foreach on tables, arrays and objects (not necessary instances, I'm not sure) which have a suitable metamethod.

[Hephi]

Thanks, I didn't know the foreach loop worked with AILists as well, I've been using it only for arrays like

foreach(route in routeArray){...}

It took me a while to understand the difference between key and value.
Now I can use

foreach(route, dummy in List)

where I could use the dummy if I had valuated the list before.

[honnes]

Just to make a guess what could have been the cause of the previous while loop. I thought that in while loops, that the condition is being checked after the while loop has taken place, so that could be why the last entry is shown twice.

If you're not a fan of the foreach in squirrel, you could use the following:

Untested, not sure if it's like this, but I guess it is:

Code: Select all

do 
{
//code
}while( <statement> )

[honnes]

That is awesome! Didn't knew you could use the foreach loop for AI*List. I have been using it only for Squirrel arrays. The foreach loop saves so much typing that could go wrong.

Never thought someone like you would still learn something in the OpenTTD developing section after being here for 6 years

Note: It's just meant as a positive joke, nothing offensive If you feel different about it, let me know and i'll delete this post

[Zuu]

Hehe, no offense taken. Yes one can never learn enough.

[Hephi]

I thought the while(){...} evaluated first and then executed and
the do{...}while() executed one time at least and then evaluated

[Blustuff]

I thought the while(){...} evaluated first and then executed and
the do{...}while() executed one time at least and then evaluated

And you were right.

Never thought someone like you would still learn something in the OpenTTD developing section after being here for 6 years

Actually, Squirrel isn't used by AI developpers for six years. I don't know when Squirrel have been choosen as the new AI language. And the manual is actually so inaccurate that the only way to know everything about squirrel is to read the source code of the compiler / virtual machine or to make thousands of weird tests.

[Hephi]

The foreach loop takes as parameters either (value in list) or (key, value in list). If you only wanted the values then you could omit the key (though you cant omit the value and only get the key).

Actually I believe you can omit the value and get the key.

Code: Select all

tile_list.AddTile(aTile);
tile_list.AddTile(bTile);
tile_list.AddTile(cTile);
foreach(tile in tile_list)
{
  AILog.Info("tile = "+tile);
} 

This would give me the tiles I put in the list without having to write foreach(tile, dummy in list).

[Zuu]

No, in that case you will get the values, not the keys.

[Hephi]

ok, I see the error of my ways now