The Objective-C 2.0 Programming Language: Formal Protocols

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Formal Protocols

Formal protocols are declared using the @protocol directive:

@protocol ProtocolName < protocol list >

method declarations

@end

The list of incorporated protocols and the method declarations are optional. The protocol must import the header files that declare any protocols it incorporates.

You can create a forward reference to a protocol using the @protocol directive in the following manner:

@protocol ProtocolName;

Within source code, protocols are referred to using the similar @protocol() directive, where the parentheses enclose the protocol name.

Protocol names listed within angle brackets (<...>) are used to do three different things:

In a protocol declaration, to incorporate other protocols (as shown earlier)
In a class or category declaration, to adopt the protocol (as shown in “Classes” and “Categories”)
In a type specification, to limit the type to objects that conform to the protocol

Within protocol declarations, these type qualifiers support remote messaging:

Type Qualifier	Definition
`oneway`	The method is for asynchronous messages and has no valid return type.
`in`	The argument passes information to the remote receiver.
`out`	The argument gets information returned by reference.
`inout`	The argument both passes information and gets information.
`bycopy`	A copy of the object, not a proxy, should be passed or returned.
`byref`	A reference to the object, not a copy, should be passed or returned.

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Last updated: 2008-02-05

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