How Do I Declare A Block in Objective-C?

As alocal variable:

returnType(^blockName)(parameterTypes) = ^returnType(parameters) {...};

As aproperty:

@property (nonatomic, copy,nullability)returnType(^blockName)(parameterTypes);

As amethod parameter:

- (void)someMethodThatTakesABlock:(returnType(^nullability)(parameterTypes))blockName;

As anargument to a method call:

[someObject someMethodThatTakesABlock:^returnType(parameters) {...}];

As atypedef:

typedefreturnType(^TypeName)(parameterTypes);

TypeNameblockName = ^returnType(parameters) {...};