AS3 Array "for each ... in" performance vs. for loop, and guaranteed in order?
actionscript-3, flash
Solution
As demonstrated by Jackson Dunstan, who compared `for`, `for each` and `for in` with different collections (arrays, vectors, etc), the performance ranking is (from fastest to slowest):
- `for`
- `for each`
- `for in` (extremely slow)
In all cases `for` is the fastest of all. In particular when used with arrays or vectors, `for` has an overwhelming performance. Those are the numbers for all collections (smaller means faster):
Problem
This question is really twofold: How does `for each` looping over an Array compare performance-wise with a simple `for` loop through its elements? Does a loop guarantee in order traversal? The following code says yes: ``` var sample_array:Array = []; for (var i:uint = 0; i < 10000; i++) sample_array.push(i); i = 0; for each(var value:uint in sample_array) { sample_array[i++] = value; } trace('in order was:', check_in_order(sample_array)); function check_in_order(array:Array):Boolean { for (var i:uint = 0, l:uint = array.length; i < l; ++i) { if (array[i] != i) return false; } return true; } ``` but I have heard other (senior-level) engineers swear up and down that the traversal does not always proceed in ascending order! Is this true?