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In Objc I use CGImageRelease method after the treatment of an image. But in Swift this method is not available.

On the Apple documentation after Retaining and Releasing Images there is a 2 Objective-C symbols hidden

My question is, why is there no more CGImageRelease in Swift ? And have we to call another method to replace it ?

Thanks !

Shruti Thombre
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Jean Lebrument
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2 Answers2

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CGImage is now managed by ARC. CGImageRelease() is no longer required on it. You can know this by looking in CGImage.h and noting that it includes the macro CF_IMPLICIT_BRIDGING_ENABLED. This indicates that Apple has audited this file to make sure it conforms to memory-management naming conventions so ARC can memory manage objects returned from functions in this file.

EDIT: I was reading over this and realized I was misleading. I don't mean to say that CGImageRelease isn't needed in ObjC (which is pretty much what I implied here…) I just mean that because of the auditing, Swift is able to handle it. In ObjC code, you still need to release these objects.

Rob Napier
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  • I doubt it. ARC introduces a number of restrictions that are pretty easy to avoid in ObjC, but extremely common in C. You can't put an ARC-managed element in a `struct` for instance. It is tricky to pass an ARC-managed element as a `void*`. Apple's focus is on Swift, and I doubt they would spend a lot of time enhancing C. They would tend, IMO, to spend that time improving Swift as a replacement for whatever you were doing in C. – Rob Napier Mar 18 '15 at 14:55
  • If _CGImageRelease_ is not needed anymore why memory usage is increasing everytime we use _context.createCGImage_ – Hope Dec 21 '15 at 07:57
  • @the It depends on the specifics of your case. Open a question that with code that reproduces your symptom and a description of exactly what you're seeing. – Rob Napier Dec 21 '15 at 13:15
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There is no more CGImageRelease in Swift, and there is no another method to replace it.

  • Swift uses ARC exclusively, so there’s no room for a call to CFRelease or __bridge_retained.
  • For types returned from C functions, we can call takeRetainedValue() / takeUnretainedValue() to get a Swift-managed value.
  • With the macro CF_IMPLICIT_BRIDGING_ENABLED, that turn on the Clang arc_cf_code_audited, Swift can handle the memory management for return value

For detail: https://nshipster.com/unmanaged/

Jirui
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