Question

I have read “What’s new in Xcode”,but I can’t find the official explanation for this feature.
Where can I find the official explanation? Which documentation? Thanks.

Answer 1

You can find this in the Apple documentation in Objective-C Programming Language: Declared Properties under “Property Implementation Directives”. Whether or not an ivar is synthesized automatically depends on what runtime you are using:

There are differences in the behavior of accessor synthesis that depend on the runtime (see also “Runtime Difference”):

• For the legacy runtimes, instance variables must already be declared in the @interface block of the current class. If an instance variable of the same name as the property exists, and if its type is compatible with the property’s type, it is used—otherwise, you get a compiler error.
• For the modern runtimes (see “Runtime Versions and Platforms” in Objective-C Runtime Programming Guide), instance variables are synthesized as needed. If an instance variable of the same name already exists, it is used.

iOS always uses the modern runtime so you never need to declare ivars explicitly.