Expression help - Error: cannot assign value

[Phi.Def]

Hi, I have a simple 2-item array (an x/y point position) and I want to change the value of the first item, but I'm getting an "Error: cannot assign value" on the line that attempts to change that value. Can anyone tell me what's going wrong? Here's my code:

xyPos = effect("Down Position")("Point");
if (thisComp.layer("Control").effect("Center Letter")("Checkbox") > 0){
xyPos[0] = xyPos[0]+88;
}
xyPos

Thanks!

[Phi.Def]

Note: I've tried the following command instead:

xyPos[0] = 88

...and it still gives the same error.

[Mylenium]

Booleans are explicit, so you can do a proper true/ false check and of course all the rest like not returning a full array to AE or providing a fallback when the condition isn't met. This should work:

Ref = effect("Down Position")("Point");
Switch=thisComp.layer("Control").effect("Center Letter")("Checkbox");

if (xySwitch != 0){
xPos = Ref[0]+88;
}
else{
xPos=Ref[0]:
}

[xPos,Ref[1]]

Mylenium

[Dan Ebberts · Accepted solution]

I think it will work if you change your first line to this:

xyPos = effect("Down Position")("Point").value;

[Phi.Def]

This worked perfectly. Can you explain to me why? Why is the ".value" needed?

Thanks!

[Dan Ebberts]

effect("Down Position")("Point") is an object representing the Point Control. Sometimes you can get away with referencing an object like that and the expression engine will figure out that you really wanted to use the value of that object, but not always. Sometimes you have to tell it explicitly with .value. So you can either just always stick .value in there when referencing expression controls, or do it when that error pops up.