IndexOf() not working

Question

In ActionScript 3, it seems like indexOf is not working when I try to find something like [int, int].

For example:

var array:Array = new Array();
array.push([5, 6]);
trace(array.indexOf([5, 6])); //-1

I wonder if I'm missing something here.

Answer 1

Arrays, like all non-primitive types in AS3, are checked by reference, not by value. Whenever you create a new instance of an object (like an array), the variable is actually a pointer to a location in memory where the object resides.

For this reason, your code won't work because you're comparing pointers to two different arrays. The language doesn't know (or care) about the contents of the objects, all it's looking to compare are the memory locations (ie the reference) to the two objects.

If we look at your code:

var array:Array = new Array();/
array.push([5, 6]);
trace(array.indexOf([5, 6])); //-1

You are actually declaring three different arrays, each with its own location in memory. Firs you create the array var, onto this you push a new array, and in this you then try to search for a new array (in indexOf([5, 6]) you are declaring a new array in-line). For this reason the search returns false, because the references do not match - even if the contents of the arrays do.

var array:Array = new Array();
var subArray:Array = [5, 6];
array.push(subArray);
trace(array.indexOf(subArray)); // 0

...this works because the reference to the array matches.

Primitive types - Numeric, Boolean, String, are compared by value eg

var a:int = 10; var b:int = 10; trace(a == b);//True

where reference types are not:

var a:Array = [5]; var b:Array = [5]; trace(a == b);//False

It would be time-consuming for the player to compare all properties of two different objects before declaring them 'equal' or not (as most complex data types do not have a distinct 'value' in the same way that a number does), so for anything non-primitive, lookups and comparisons are done by reference.

Hope this helps.

Answer 2

Everytime you write [5, 6] you are creating a new instance of [int, int]. When doing indexOf() and comparing objects, it only checks if that particular instance exists (by checking for a reference to the object) in the array, not another instance with the same values. You could change your code as follows for it it work as expected:

var arr0:Array = [5, 6];
var array:Array = new Array(); 
array.push(arr0); 
trace(array.indexOf(arr0)); //should print 0 now instead of -1