In our sample, all we have to worry about is the reference counters-both the global and the object counter-and the "database" structures.
在我们的例子里,我们全部要关心的是引用计数—全局和对象计数—和“数据库”结构。
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Overhead in memory is very small: You basically have a 4- byte overhead per interface (the vtable pointers in the object's instance data) plus 4 bytes for the referencecounter.