CODEWITHSUNDEEP
objective-cpointersstruct
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Reputation: 132

Why doesn't objective-c allow pointers to a struct?

I was wondering why objective-c (ARC) does not allow me to use a pointer to a struct (NSPoint, in this case)

My code works without one, I just want to question why it doesn't allow it as I have not found a reason on Google for it.

My current guess is because structs cannot contain objects, but I want to double check that; and want to know where the struct itself is saved. Thanks!

Upvotes: 2

Views: 1277

Answers (1)

MrHappyAsthma
MrHappyAsthma

Reputation: 6522

When migrating to ARC, the compiler no longer allowed this due to the complexity of how the struct containing object pointers would be initialized, copied, moved, or destroyed.

Apple called this out in the Transitioning to ARC guides line the "ARC Enforces New Rules" section.

  • You cannot use object pointers in C structures.

    • Rather than using a struct, you can create an Objective-C class to manage the data instead.

However this is now allowed in LLVM as of this commit.

To quote directly from the commit message:

Declaring __strong pointer fields in structs was not allowed in Objective-C ARC until now because that would make the struct non-trivial to default-initialize, copy/move, and destroy, which is not something C was designed to do. This patch lifts that restriction.

Special functions for non-trivial C structs are synthesized that are needed to default-initialize, copy/move, and destroy the structs and manage the ownership of the objects the __strong pointer fields point to. Non-trivial structs passed to functions are destructed in the callee function.

Upvotes: 3

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