Can I use an instantiated Object as an Array Key?

Question

For example:

$product = new Product(\"cat\");

if(isset($sales[$product])){
     $sales[$product]++;
}
else{
     $sales[$product] = 1;
}

Answer 1

From the docs:

Arrays and objects can not be used as keys. Doing so will result in a warning: Illegal offset type.

You could give each instance a unique ID or override __toString() such that it returns something unique and do e.g.

$array[(string) $instance] = 42;