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Protocols

Protocols declare methods that can be implemented by any class. Protocols are useful in at least three situations:

• To declare methods that others are expected to implement

• To declare the interface to an object while concealing its class

• To capture similarities among classes that are not hierarchically related

Contents:

Declaring Interfaces for Others to Implement
Methods for Others to Implement
Declaring Interfaces for Anonymous Objects
Non-Hierarchical Similarities
Formal Protocols
Informal Protocols
Protocol Objects
Adopting a Protocol
Conforming to a Protocol
Type Checking
Protocols Within Protocols
Referring to Other Protocols

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