State the difference between strong, weak, read-only, and copy.

Strong: This PropertyProperty maintains a reference to PropertyProperty throughout the lifetime of an object. When you declare strong, you expect to “own” the object you are referencing. Data you assign to this PropertyProperty will not be destroyed as long as you or any other object references it strongly.

Weak: It means that you should keep the object in memory as long as someone points to it strongly, and you don’t require control over its lifetime.

Read-only: Initially, an object’s PropertyProperty can be defined, but it cannot change or alter.

Copy: This attribute is an alternative to a strong attribute. To take ownership of a current object, it creates a copy of whatever you assign to the PropertyProperty, then takes ownership of that copy.