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

If the object is a simple predefined classes made with new stdClass() it may be valid option to use the json representation of this class with json_encode.

$product = new stdClass();
$product->brand = "Acme";
$product->name = "Patator 3.14";

$product_key = json_encode($product);

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

But keep in mind that the equality of two objects is always a business model choice and must be carefully designed.