工厂对象实现取消引用逻辑。
稍后，你从关联设备取消画笔对象并销毁该对象。
Later on, you deselect the pen object from the device context and destroy the object.
核心数据对象去除不取消所有的关系？
Removal of core data object does not nullify all of its relations?
从堆栈中弹出对象引用并取消装箱为值类型指针。
The object reference is popped from the stack and unboxed to a value type pointer.
从堆栈中弹出对象引用并取消装箱为值类型指针。
The object reference is popped from the stack and unboxed to a value type pointer.
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