Describes elements of best practice when writing code with Objective-C using ARC.
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Unlike regular categories, a class extension can add its own properties and instance variables to a class. If you declare a property in a class extension, like this: @interface XYZPerson () @property NSObject *extraProperty; @end
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↑これでヘッダーに載せないフィールドが書ける
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It’s also possible to use a class extension to add custom instance variables. These are declared inside braces in the class extension interface: @interface XYZPerson () { id _someCustomInstanceVariable; } ... @end
