readme.md

Reasoning behind the macro

#define KINDOF_CAST(arg) ((__kindof typeof(arg))(arg))

UICollectionViewFlowLayout* flowLayout = KINDOF_CAST(self.collectionView.collectionViewLayout);

The macro works at compile time. It relies on the collectionViewLayout property declaration type. So the expression results in

UICollectionViewFlowLayout* flowLayout = (__kindof UICollectionViewLayout)(self.collectionView.collectionViewLayout);

The __kindof UICollectionViewLayout type silences the compiler's "type mismatch" warnings because UICollectionViewFlowLayout is a child of UICollectionViewLayout.

The templates above do the runtime checks so these casts might co-exist depending on the "safety" level chosen by the programmer.

objc_kind_of_compile_time_macro.h

#define KINDOF_CAST(arg) ((__kindof typeof(arg))(arg))

// By Scherbinin Anatoly from the cocoa chat ("Какао-чат: Cocoa, Xcode, objective C")

usage.mm

UICollectionViewFlowLayout* flowLayout = KINDOF_CAST(self.collectionView.collectionViewLayout);

Some runtime cast example cat be found here https://gist.github.com/dodikk/4a0f1d98faa7c1336551#file-objccastfunctions-hpp-L23