Flex - Should I do a == check before I assign a boolean? - apache-flex

Question

Should I do it like this:
if (DeviceDisplay.IsSpeedAvailable == false){
DeviceDisplay.IsSpeedAvailable = true;
}
or
DeviceDisplay.IsSpeedAvailable = true;
I thought I saw that flex/as3 does an internal check on booleans before they are assigned to make sure you are re-assigning stuff but I can't find it to confirm.
I know this is small stuff but I'd like to know.

Answer 1

If you are using the [Bindable] tag for property notification, the event will not get fired if the value doesn't change. If you look at the generated code, it will check to see if the value has changed. If it has not changed, it does not fire an event. If it has changed, the event fires.
Because of this, you are only complicating your code (and being redundant) by checking before setting the value.
If you are simply setting a normal boolean (without change notification), then you don't gain anything by checking first, so you don't need to check.
If you are using some sort of custom mutator in which setting the value causes a side effect, then you should check it inside of your mutator, but never outside of it. Like this:
public function set foo(value):void {
if(value == _foo)
return;
_foo = value;
doSideEffect();
}
This is the pattern, for instance, that [Bindable] writes for you when you use it (where doSideEffect fires a change event).
In my opinion, this is the only time you should ever check the value of a bool before setting it.

Answer 2

AS doesn't do an internal check before setting a boolean, so if it is important not to reassign a value to it (such as avoiding a change listener from firing), then you should do the check first.
If it is that critical that the value not be re-assigned, you should consider writing your own setter method for it (or overriding an existing) which checks the value before setting the value. This way every assignment to that variable has the check - which means less assumptions and errors down the road.
Here's a test script to illustrate that a check isn't made - which makes sense considering that it would take extra processing to do that automatically.
<mx:Script>
<![CDATA[
import mx.controls.Alert;
private var _bool : Boolean = true;
private function set myBool ( val : Boolean ) : void {
_bool = val;
mx.controls.Alert.show('set!');
}
private function get myBool () : Boolean {
return _bool;
}
]]>
</mx:Script>
<mx:VBox>
<mx:Button label="set true" click="myBool = true;"/>
<mx:Button label="set false" click="myBool = false;"/>
</mx:VBox>