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Editorial Team
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Asked: 2026-06-02T06:57:36+00:00

In Objective-C, we can add @property and @synthesize to create a property — like

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In Objective-C, we can add @property and @synthesize to create a property — like an instance variable with getter and setter which are public to the users of this class.

In this case, isn’t it just the same as declaring an instance variable and making it public? Then there won’t be the overhead of calling the getter and setter as methods. There might be a chance that we might put in validation for the setter, such as limiting a number to be between 0 and 100, but other than that, won’t a public instance variable just achieve the same thing, and faster?

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  1. Editorial Team

    Even if you’re only using the accessors generated by @synthesize, they get you several benefits:

    1. Memory management: generated setters retain the new value for a (retain) property. If you try to access an object ivar directly from outside the class, you don’t know whether the class might retain it. (This is less of an issue under ARC, but still important.)

    2. Threadsafe access: generated accessors are atomic by default, so you don’t have to worry about race conditions accessing the property from multiple threads.

    3. Key-Value Coding & Observation: KVC provides convenient access to your properties in various scenarios. You can use KVC when setting up predicates (say, for filtering a collection of your objects), or use key paths for getting at properties in collections (say, a dictionary containing objects of your class). KVO lets other parts of your program automatically respond to changes in a property’s value — this is used a lot with Cocoa Bindings on the Mac, where you can have a control bound to the value of a property, and also used in Core Data on both platforms.

    In addition to all this, properties provide encapsulation. Other objects (clients) using an instance of your class don’t have to know whether you’re using the generated accessors — you can create your own accessors that do other useful stuff without client code needing changes. At some point, you may decide your class needs to react to an externally made change to one of its ivars: if you’re using accessors already, you only need to change them, rather than make your clients start using them. Or Apple can improve the generated accessors with better performance or new features in a future OS version, and neither the rest of your class’ code nor its clients need changes.

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