property inheritance: Auto property synthesis will not synthesize property
inheritance, objective-c, properties
Solution
You need to declare the property as read-write on the owning class (`A`), and then redeclare on the subclass (`B`) to make the compiler aware that you want to use it there. So, `A` hosts the accessor method and `B` uses it. Generally you don't want `B` to create another accessor method so you can use `@dynamic` to tell the compiler that the superclass (technically, just another class) will provide the implementation.
Note that you can also declare a category (not extension) on `A`, in `B`.m which declares the accessor method explicitly (not using a property, just a method) as that is what you're actually interested in (you don't actually want any of the other things that a property specifies and you don't really want the maintenance overhead of ensuring that the property attributes match in the super and subclass)...
Problem
Abstract: This question is about inheritance of properties in combination with different read/write accesses from inside and outside of the classes inheriting the property from one another. Details: I have one class `A` and another class `B`, which inherits from `A`. There is the property `someProperty` declared in `A`. I want the property to be readonly from outside these classes and read/write from inside. With only one class, this is dead-simple: You declare the property in the `.h` as readonly and you declare it again as readwrite in the .m inside of a category. Done. But with the two classes, one deriving from the other, I get the below compiler warning in `B`: Auto property synthesis will not synthesize property 'someProperty' because it is 'readwrite' but it will be synthesized 'readonly' via another property Here is the code: A.h: ``` #import <Foundation/Foundation.h> @interface A : NSObject // This property shall be readonly from outside, but read/write from subclasses @property (readonly) SInt32 someProperty; @end ``` A.m: ``` #import "A.h" @implementation A @end ``` B.h: ``` #import <Foundation/Foundation.h> #import "A.h" @interface B : A @end ``` B.m: ``` #import "B.h" @interface B () // compiler warning in the following property declaration: // /Users/.../B.m:12:41: Auto property synthesis will not synthesize property // 'someProperty' because it is 'readwrite' but it will be synthesized // 'readonly' via another property @property (readwrite) SInt32 someProperty; @end @implementation B @end ``` Why does this warning appear and how should I structure my code to avoid it?