October 2017
Intermediate to advanced
210 pages
5h 32m
English
Content preview from Swift 4 Protocol-Oriented Programming - Third Edition
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Optional requirements
There are times when we want protocols to define optional requirements. An optional requirement is a method or property that is not required to be implemented. To use optional requirements, we need to start off by marking the protocol with the @objc attribute.
It is important to note that only classes can adopt protocols that use the @objc attribute. Structures and enumerations cannot adopt these protocols.
To mark a property or method as optional, we use the optional keyword. The following example shows how we would create both an optional property and also an optional method:
@objc protocol Phone { var phoneNumber: String {get set} @objc optional var emailAddress: String {get set} func dialNumber() @objc optional func ...Become an O’Reilly member and get unlimited access to this title plus top books and audiobooks from O’Reilly and nearly 200 top publishers, thousands of courses curated by job role, 150+ live events each month,
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