How does sender.selected = ! sender.selected toggle between selected states?

I'm very new to Objective-C so sorry if this is extremely obvious to many of you, but I'm trying to work out how the following piece of code is actually working:

- (IBAction)chooseColour:(UIButton *)sender {
 sender.selected = !sender.isSelected;
}

Now it obviously toggles between the selected and unselected states of the button sending the action, but what is the code 'sender.selected = !sender.isSelected' actually saying? Is it just 'set the sender selected property to the opposite (i.e. ! not) of the getter'? So if the getter is 'getting' the current selected value as true then it sets the selected property as !true i.e false. Or is this a piece of convenience code that I'm not yet privy to? Because it also seems that '!sender.isSelected' simply means not selected as in

if (!sender.isSelected){
statement
}

i.e. do statement if the sender is not selected. This is no doubt really obvious, just I'm a bit confused with it at the moment.

Thanks!

Solution

You are entirely correct, it's calling the getter to obtain the value and calling the setter with the NOT (!) of the value. It isn't Objective-C, it's plain C syntax.