CODEWITHSUNDEEP
objective-c
Joseph Lin
Joseph Lin

Reputation: 3334

In objective-c, why 'typedef NSString * MyString' is preferred over 'typedef NSString MyString'?

Option 1: typedef NSString MyString

Option 2: typedef NSString * MyString

Question

In Objective-C, both statement are valid, but from what I've seen people overwhelmingly choose option 2 over option 1. Is there a technical reason to that, or is it more of a convention?

Why I preferred option 1

Option 2 hides the fact that MyString is a pointer. This might be the intention, but in objective-c it's more often than not that you do want to know whether you're dealing with a primitive type or a reference type.

In C, at least the convention is to give it a name like MyStringRef to emphasize that it's a pointer, but I don't think I ever seen anyone does that in objective-c.

But option 1 doesn't play nicely with Swift

And then there's Swift. Both option 1 and option 2 works perfectly fine when bridged to swift, but if I try to mark option1 as a enum- typedef NSString MyString NS_STRING_ENUM; FOUNDATION_EXPORT MyString * const MyStringOne;

the compiler starts to freak out. Syntax highlight and auto-completion breaks all the time. And something like var x = MyString.one chokes the compiler straight out, leaving only the Segmentation fault: 11 error.

Upvotes: 3

Views: 910

Answers (1)

CRD
CRD

Reputation: 53000

You are correct that this pattern is used when declaring “string enums” in Objective-C.

You ask why including the * in the typedef is preferred.

Well usually the reason is just one of subjective preference, either approach is valid. Note that Core Foundation uses type names such as CFStringRef where the * is hidden but the name contains Ref to indicate this, however Objective-C does not follow and use NSStringRef.

However you have found an objective reason to follow the usual pattern - the Swift compiler (at least in Xcode 8.2.1 I used and which one you used) is a sensitive creature and blows itself up with a memory fault if you use the other pattern.

First submit a bug to Apple (test first in Xcode 9 if you have it).

Then stick with the “preferred” pattern, unless you enjoy watching Swift commit compilercide ;-)

Upvotes: 2

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