Hi Steve,
I thought it'd be useful to have some actual figures, so I put together a quick
test. Test code was as follows:
package
{
import flash.display.Sprite;
import flash.utils.getTimer;
/**
* @author Piers Cowburn
*/
public class ArrayAccessTest extends Sprite
{
private const ITERATIONS:int = 1000000;
public function ArrayAccessTest()
{
trace("Starting tests...");
var startTimer:int;
var i:int;
var j:int;
var array:Array = [new TestClass(), new TestClass(), new
TestClass()];
var vector:Vector.<TestClass> = new Vector.<TestClass>();
vector.push(new TestClass());
vector.push(new TestClass());
vector.push(new TestClass());
var numItems:int = array.length;
var implicitCast:TestClass;
var explicitCast:TestClass;
var asCast:TestClass;
//
// [Array 0a] Array access test
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
array[j].someMethod();
}
}
trace("[Array 0a] Array access test: " + (getTimer()-startTimer));
//
// [Array 1a] Implicit cast test
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
implicitCast = array[j];
implicitCast.someMethod();
}
}
trace("[Array 1a] Implicit cast test: " + (getTimer()-startTimer));
//
// [Array 2a] Explicit cast test
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
explicitCast = TestClass(array[j]);
explicitCast.someMethod();
}
}
trace("[Array 2a] Explicit cast test: " + (getTimer()-startTimer));
//
// [Array 3a] As cast test
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
asCast = array[j] as TestClass;
asCast.someMethod();
}
}
trace("[Array 3a] As cast test: " + (getTimer()-startTimer));
//
// [Array 0b] Array access test (two operations)
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
array[j].someMethod();
array[j].someOtherMethod();
}
}
trace("[Array 0b] Array access test (two operations): " +
(getTimer()-startTimer));
//
// [Array 1b] Implicit cast test (two operations)
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
implicitCast = array[j];
implicitCast.someMethod();
implicitCast.someOtherMethod();
}
}
trace("[Array 1b] Implicit cast test (two operations): " +
(getTimer()-startTimer));
//
// [Array 2b] Explicit cast test (two operations)
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
explicitCast = TestClass(array[j]);
explicitCast.someMethod();
explicitCast.someOtherMethod();
}
}
trace("[Array 2b] Explicit cast test (two operations): " +
(getTimer()-startTimer));
//
// [Array 3b] As cast test (two operations)
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
asCast = array[j] as TestClass;
asCast.someMethod();
asCast.someOtherMethod();
}
}
trace("[Array 3b] As cast test (two operations): " +
(getTimer()-startTimer));
//
// [Vector 0a] Vector access test
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
vector[j].someMethod();
}
}
trace("[Vector 0a] Vector access test: " + (getTimer()-startTimer));
//
// [Vector 1a] Implicit cast test
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
implicitCast = vector[j];
implicitCast.someMethod();
}
}
trace("[Vector 1a] Implicit cast test: " + (getTimer()-startTimer));
//
// [Vector 2a] Explicit cast test
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
explicitCast = TestClass(vector[j]);
explicitCast.someMethod();
}
}
trace("[Vector 2a] Explicit cast test: " + (getTimer()-startTimer));
//
// [Vector 3a] As cast test
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
asCast = vector[j] as TestClass;
asCast.someMethod();
}
}
trace("[Vector 3a] As cast test: " + (getTimer()-startTimer));
//
// [Vector 0b] Vector access test (two operations)
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
vector[j].someMethod();
vector[j].someOtherMethod();
}
}
trace("[Vector 0b] Vector access test (two operations): " +
(getTimer()-startTimer));
//
// [Vector 1b] Implicit cast test (two operations)
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
implicitCast = vector[j];
implicitCast.someMethod();
implicitCast.someOtherMethod();
}
}
trace("[Vector 1b] Implicit cast test (two operations): " +
(getTimer()-startTimer));
//
// [Vector 2b] Explicit cast test (two operations)
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
explicitCast = TestClass(vector[j]);
explicitCast.someMethod();
explicitCast.someOtherMethod();
}
}
trace("[Vector 2b] Explicit cast test (two operations): " +
(getTimer()-startTimer));
//
// [Vector 3b] As cast test (two operations)
startTimer = getTimer();
for (i = 0; i < ITERATIONS; ++i)
{
for (j = 0; j < numItems; ++j)
{
asCast = vector[j] as TestClass;
asCast.someMethod();
asCast.someOtherMethod();
}
}
trace("[Vector 3b] As cast test (two operations): " +
(getTimer()-startTimer));
}
}
}
And the results were:
[Array 0a] Array access test: 1631
[Array 1a] Implicit cast test: 1527
[Array 2a] Explicit cast test: 1689
[Array 3a] As cast test: 1745
[Array 0b] Array access test (two operations): 3172
[Array 1b] Implicit cast test (two operations): 2636
[Array 2b] Explicit cast test (two operations): 2817
[Array 3b] As cast test (two operations): 2841
[Vector 0a] Vector access test: 1624
[Vector 1a] Implicit cast test: 1520
[Vector 2a] Explicit cast test: 1707
[Vector 3a] As cast test: 1722
[Vector 0b] Vector access test (two operations): 3160
[Vector 1b] Implicit cast test (two operations): 2638
[Vector 2b] Explicit cast test (two operations): 2790
[Vector 3b] As cast test (two operations): 2828
I was surprised to see that using an implicit cast was fastest in all
situations, even faster than using the array access operator to make one method
call (test Array 0a vs. Array 1b). Also, you can see that storing a temporary
variable really starts to make a difference when you're making more than one
method call (difference between Array 0b and Array 1b).
HTH,
Piers
On 27 Dec 2009, at 01:26, Piers Cowburn wrote:
> *Disclaimer* This is un-benchmarked, but it's what I usually work to! If
> anyone has any corrections re. speed, I'd be glad to hear them :)
>
> AFAIK, using implicit casting rather than explicit in this case is faster, so
> A1 in your examples is faster than A2. Also, it's better to move your
> variable declaration outside the loop:
>
> var i:int = myArray.length;
> // Variable is declared once here and then reused
> var myClass:MyClass;
> while (i--)
> {
> myClass = myArray[i];
> }
>
>
> With vectors, you don't need to cast at all. However, though you can access
> your references directly from the vector using [ ], like you've done in V3,
> it will be faster to store a local reference if you're using it more than
> once. So for example:
>
> var i:int = myVector.length;
> var myClass:MyClass;
> while (i--)
> {
> // Store the reference in a temporary variable to avoid using [ ]
> unnecessarily
> myClass = myVector[i];
> myClass.someMethod();
> myClass.someOtherMethod();
> }
>
> will be faster than:
>
> var i:int = myVector.length;
> while (i--)
> {
> // This uses [ ] twice
> myVector[i].someMethod();
> myVector[i].someOtherMethod();
> }
>
>
> If you're only using the reference once though, it should be faster just to
> use [ ], so:
>
> var i:int = myVector.length;
> while (i--)
> {
> // Just using the reference once, so not defining a temporary variable:
> myVector[i].someMethod();
> }
>
> will be faster than:
>
> var i:int = myVector.length;
> var myClass:MyClass;
> while (i--)
> {
> // This is a waste as we're only using it once
> myClass = myVector[i];
> myClass.someMethod();
> }
>
>
> As I said, I don't have benchmarked figures for these, so don't take it as
> gospel, but I think this was what I read when I read it.
>
> Piers
>
>
>
>
> On 27 Dec 2009, at 00:24, Steven Sacks wrote:
>
>> var instance1:MyClass = new MyClass();
>> var instance2:MyClass = new MyClass();
>> var instance3:MyClass = new MyClass();
>>
>> var myArray:Array = [instance1, instance2, instance3];
>>
>> // QUESTION A: CASTING WITH ARRAYS
>>
>> var i:int = myArray.length;
>> while (i--)
>> {
>> // [A1] - Does Flash have to do a look up here?
>> var myClass:MyClass = myArray[i];
>>
>> // [A2] - Does casting it like this boost performance
>> var myClass:MyClass = MyClass(myArray[i]);
>>
>> // [A3] - I know using "as" is slower than direct casting
>> var myClass:MyClass = myArray[i] as MyClass;
>> }
>>
>> // QUESTION B: CASTING WITH VECTORS
>>
>> var myVector:Vector.<MyClass> = Vector.<MyClass>(myArray);
>>
>> var i:int = myVector.length;
>>
>> while (i--)
>> {
>> // [V1] - Will this avoid the lookup?
>> var myClass:MyClass = myVector[i];
>>
>> // [V2] - Or do I need to cast here even though it's a Vector?
>> var myClass:MyClass = MyClass(myVector[i]);
>>
>> // [V3] - And if so, can I do this without a lookup?
>> myVector[i].someMethod();
>>
>> // [V4] - Or do I need to do this?
>> MyClass(myVector[i]).someMethod();
>> }
>>
>>
>> Thanks in advance for anyone who can shed some light here. I believe A2/V2
>> is "fastest" but I'm not certain, and I also don't know if it's required for
>> Vector.
>> _______________________________________________
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>> [email protected]
>> http://chattyfig.figleaf.com/mailman/listinfo/flashcoders
>
>
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