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To prevent both memory leakage and dangling pointers, there is a policy of manual memory management based on a number, maintained by every reference type object, called its retain count. The rule is that other objects can increment or decrement an object’s retain count — and that’s all they are allowed to do. As long as an object’s retain count is positive, the object will persist. No object has the direct power to tell another object to be destroyed; rather, as soon as an object’s retain count is decremented to zero, it is destroyed automatically.

By this policy, every object that needs Jack to persis...

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Cover of iOS 11 Programming Fundamentals with Swift

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