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See Memory Management for the implications of this constraint. The retain attribute specifies that a retain should be invoked on the object when it is assigned, and the previous value should be sent a release message. The assign attribute is the default and implies that the generated setter uses simple assignment. The assign, retain, copy, weak, and strong custom attributes govern the setter accessor method and are mutually exclusive. If this is set, only a getter method is generated when you the property in your implementation. You can choose whether the property has an associated setter accessor method by specifying the readonly custom attribute. Bear in mind that changing the default names will invariably break the dot syntax syntactic sugar that Objective-C normally provides. You can change this by using the getter=getterName and setter=setterName custom attributes. This can prove very useful you can imagine that if you wanted to build a generic class implementing a linked list, the type of object held in each node would be of type id, since you’d then be able to store any type of object.īy default, the automatically generated accessor methods created when you a property are propertyName: and setPropertyName. The id class is a generic C type that Objective-C uses to represent an arbitrary object it’s a general type representing any type of object regardless of class and can be used as a placeholder for both a class and a reference to an object instance. Here’s a weakly typed version of the declaration, where it is declared as an object of class id: id label In the first instance, we use strong typing, declaring it as an object of the class SomeClass. Here’s a strongly typed declaration: UILabel *label However, Objective-C adds an interesting twist: it supports both strongly typed and weakly typed declarations. When instance variables are themselves objects-for instance, when the ViewController class declares a UILabel variable-you should always use a pointer type.