Wierd Squirrel Bug re: array.sort(compare_func)

[Zutty]

Hi all,

I've discovered a rather odd bug when using array.sort() with a comparison function. If I call an API function from within a comparison function I get the following error...

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dbg: [ai] [1] [S] Your script made an error: parameter 0 has an invalid type 'table' ; expected: 'instance'

For instance the following code will cause this bug. Assume that array contains objects with an id member variable...

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array.sort(function (a,b) {
	local aval = AITown.GetPopulation(a.id);
	local bval = AITown.GetPopulation(b.id);
		
	if(aval > bval) return 1
	else if(aval < bval) return -1
	return 0;
});

This is because when a squirrel function is called it requires a this environment object to work from. It would seem that an object of type table is being used, rather than an object of type instance. I can remedy this with a simple hack, by forcing my own environment object using the call() function...

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array.sort(function (a,b) {
	local aval = AITown.GetPopulation.call(a, a.id);
	local bval = AITown.GetPopulation.call(b, b.id);
	
	if(aval > bval) return 1
	else if(aval < bval) return -1
	return 0;
});

This works perfectly. The objects a and b aren't very smart choices of environment, but at least they are of the right type. Perhaps a fix for this would be to somehow cast the table that is causing this error to type instance, or just to create an instance of a dummy class.

This is in r15379. And yes I know that the above could sort of be done with an AIList valuator, but I need to sort objects not integers. The actual comparison function I'm using is more complex than this. I have just boiled it down to an example that demonstrates the bug neatly.

Just thought you'd like to know. Thanks for your attention.

----------------

Edit: by the way, if anyone is scratching their heads like I was, trying to figure out how to sort an array of objects by a variable that is not in scope, squirrel provides a thing called free variables...

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local cargo = ......

array.sort(function (a,b):(cargo) {
	return ...
}

[jui-feng]

Ah, free variables! I just passed that in as an extra parameter, but I guess free variables are the better way to go. This is a little off topic, but still: thanks!

[TrueBrain]

Ah, free variables! I just passed that in as an extra parameter, but I guess free variables are the better way to go. This is a little off topic, but still: thanks!

In fact, free variables are your worst nightmare Using lambda functions too, btw

[TrueBrain]

Hi all,

I've discovered a rather odd bug when using array.sort() with a comparison function. If I call an API function from within a comparison function I get the following error...

Code: Select all

dbg: [ai] [1] [S] Your script made an error: parameter 0 has an invalid type 'table' ; expected: 'instance'

For instance the following code will cause this bug. Assume that array contains objects with an id member variable...

One of the big design flaws of Squirrel (in my opinion, that is), is that the 'root' scope/class is in fact a 'table', where every other object you create, is an instance. So this happens from time to time. That is why we make you put everything in a class, which makes most calls with an instance .. but clearly this lambda function breaks out and is put in the root scope, with as result that the static function call is done with a table as 'self', instead of a random 'instance'. As the NoAI API is mostly static calls, it really doesn't matter what you give as first param .. it just is a bit silly that you have to worry about it

Maybe Yexo or Rubidium can find a simple way to fix it

[Yexo]

This problem was fixed in r15460.