Apart from the cases that are listed above, the only other use of an explicit synthesize would be to specify a different ivar name. However conventions are important, so my advice is to always use the default naming. If you do not explicitly use synthesize the compiler will understand your property the same way if you had written.
Personally I stop using synthesize , since it's not mandatory any more. For me the only reason to use synthesize is to link an iVar to a property.
If you want to generate specific getter and setter for it. But in the given piece of code there is no iVar , I think that this synthesize is useless. But now I think the new question is "When to use iVar? Say you're writing both a custom getter and setter, but want an instance variable to back it. For an atomic property, this is as simple as wanting a custom setter: the compiler will write a getter if you specify a setter for a monatomic property, but not an atomic property. You've specified both a getter or setter, so Xcode correctly doesn't create a backing instance variable for it.
You have two choices for making it exist. You can either change the implementation to this:. You can decide which form here you want to use. And I wouldn't be surprised if Apple fixes this, or even already has. There is only one time that auto synthesise does not work: If you overwrite but the setter AND the getter method then you will need to synthesise the iVar. You are fine if you just override the setter or if you just override the getter. But if you do both then the compiler won't understand it and you will need to synthesise it manually.
Property synthesis is required when a property is declared in a protocol. It will not be automatically synthesized in an implementing interface. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. When should I use synthesize explicitly? Ask Question. Asked 8 years ago. Active 2 years, 7 months ago.
Viewed 63k times. When should I add synthesize explicitly to my code? Improve this question. Alex Zavatone 3, 32 32 silver badges 50 50 bronze badges.
The sample code might be old. Basically, use it unless it turns into a problem for example, properties in delegates will not be auto-synthesized — borrrden. And, the setting method should be named setProperty:. In this case the method would be named "setPosts", so one might call the method on an instance of our PostsController class like this: [postsController setPosts:newPosts].
Here is what the two methods would look like if we explicitly wrote the accessor methods ourselves. Beginning with Xcode 4. We simply declare the property in our interface, and Xcode takes care of the rest; creating the necessary instance variable as well as the accessor methods. This is done when compiling our code using the new LLVM compiler clang when we do not explicitly define these ourselves. We can still declare the accessor methods ourselves if we want to override this default behavior.
The getter and setter methods for an atomic property need to ensure that they do not interfere with each other when called from different threads.
For example, the getter method should not be able to retrieve a value whilst the setter is in the process of setting it. This synchronisation means that you cannot implement one of the accessors and have the compiler supply the other.
I mention it here in passing as the issue can catch you out since properties are atomic by default. So for example if we declare the following property:. This is actually an atomic property so if we add our own implementation of the getter method but do not also supply the setter we will get a compiler warning:.
The solution is to either implement the setter or change the property to nonatomic assuming you do not need the accessors to be thread-safe. There is no reason why you have to go back and start deleting synthesize statements from existing code since the default action maintains backwards compatibility. Of course if you enjoy deleting code or you are modifying a class it might be an idea to clean things up when possible.
I came across a good example of the issues you can get with existing code whilst playing around with the WorldFacts project I created recently to experiment with storyboards. This project was created using an Xcode template and includes core data. You can refer to the project in my CodeExamples repository for the final result but below are my notes on attempting to remove all of the synthesize statements from this project:.
The class implementation includes synthesize statements for each property but whoever created the template decided to use a double underscore to prefix the core data instance variable names but not the window :. The Xcode template follows the common pattern of lazily instantiating the core data stack in the getter method for each of the core data properties. I will not show the code here but they obviously refer to an instance variable with a double underscore e.
This could cause an issue if we were relying on the compiler to synthesize the instance variable. However in this case we are dealing with a readonly property where we implement the getter so the compiler will leave us alone.
This means we have to leave the synthesize statement to explicitly request the compiler generate the instance variable. You could also rename the variables to use a single underscore but in this case I saw little point in making the change. Here both the managedObjectContext and fetchedResultsController properties use a double underscore for the ivar name.
In addition we implement getter methods for both the fetchedResultsController and decimalFormatter properties. It is a keyword of Objective-C language. When you define a series of variables, you need to write a lot of getter and setter methods, and their forms are similar, so Xcode provides property and synthesize properties, property is used in t Stands for the "Objective-C" sign, which proves that you are using the Objective-C language Objective-C language keywords, property is paired with synthesize.
Property and synthesize usage in Objective-C 1.
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