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Memory and ARC

Core Foundation and ARC

When you handle a Core Foundation object returned by a C API like SecItemCopyMatching or CGImageSource in Swift, when do you use Unmanaged, takeRetainedValue(), and takeUnretainedValue()? Tie it to the Create/Get rule.

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Core Foundation encodes ownership in the function name: a Create/Copy function returns a +1 value the caller owns, so you take it with takeRetainedValue(), and a Get function returns +0, so you use takeUnretainedValue(). With an Unmanaged result that choice is yours, and getting it backwards means either a leak or an over-release crash.

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