What is the difference between the code (i) and (ii) written below ?
(i)
var obj:Object = new Object();
obj.attribute = value ;
(ii)
var obj:Object = new Object();
obj["key"] = value;
Are there any run-time implications if I write this :
var obj:Object = new Object();
obj.somekey = value1 ;
obj["someKey"] = value2 ;
Please explain.
The difference is in the lookup mechanism: If you use the dot syntax, the compiler will know at compile time that you are accessing a property of that object. If you use the bracket syntax, the actual lookup of the property is done at runtime, and there will have to be more type checking - after all, you could compose the key string dynamically, the value could change, or you could even be calling a function instead of a variable, etc.
The result is a significant difference in performance: Bracket syntax takes about three times as long to execute as dot syntax.
Here's a little speed test to illustrate my point:
var start : int = getTimer();
var obj:Object = { something : "something" };
for (var i : int = 0; i < 100000000; i++) {
var n:String = obj.something;
}
trace ("Time with dot syntax: "+(getTimer() - start));
start = getTimer();
for (i = 0; i < 100000000; i++) {
var o:String = obj["something"];
}
trace ("Time with bracket syntax: "+(getTimer() - start));
If the two were the same, except for notation, they should take exactly the same amount of time. But as you can see, this is not the case. On my machine:
Time with dot syntax: 3937
Time with bracket syntax: 9857
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