When I'm declaring variables as
'weak' may only be applied to class and class-bound protocol types
weak is a qualifier for reference types (as opposed to value types, such as
structs and built-in value types).
Reference types let you have multiple references to the same object. The object gets deallocated when the last strong reference stops referencing it (weak references do not count).
Value types, on the other hand, are assigned by copy. Reference counting does not apply, so
weak modifier does not make sense with them.