CODEWITHSUNDEEP
iphoneobjective-ciossyntax
Robert
Robert

Reputation: 38213

Objective C: Is there a difference between these two statements?

Setup:

@interface Base : NSObject {}
@end

@interface Subclass : Base {}
@end

…

Subclass* sub = …;

Is there a difference between:

// No explicit cast.
Base* base = sub;

and:

// Explicit cast, but does this actually DO anything different at runtime?
Base* base = (Base*) sub;

Upvotes: 2

Views: 159

Answers (4)

zoul
zoul

Reputation: 104065

Treating a subclass like its parent class is quite common and safe. (Unless you’re misusing inheritance in your design.) The cast does nothing extra in runtime and is not needed during compilation; it’s completely useless as far as the machine is concerned.

Upvotes: 3

Daniel Bleisteiner
Daniel Bleisteiner

Reputation: 3310

Your casted statement is only valid if base really points to an instance of ClassSuper. Since ClassBase includes more types then ClassSuper your cast might fail during runtime!

Your first statement though won't fail because Objective-C doesn't really care about the type during assignment. So your ClassSuper* super is more an id super during runtime. The cast though will be verified and throw errors if not fulfilled.

Upvotes: -1

Kay
Kay

Reputation: 13146

Hmmh Warning: incompatible Objective-C types initializing 'struct AbstractClass *', expected 'struct ConcreteClass *'

Upvotes: 0

hoha
hoha

Reputation: 4428

You will get a compiler warning about ClassSuper* super = base; since not every ClassBase instance is ClassSuper instance. So if you really know what you do you should make explicit cast to stop compiler from whining.

Upvotes: 0

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