What, again?

What, again?

Posted May 12, 2007 6:55 UTC (Sat) by jwalden (guest, #41159)
In reply to: What, again? by njs
Parent article: The Rise of Functional Languages (Linux Journal)

when a resource has dynamic extent, you use a smart pointer, which has explicit semantics about when it will be freed (i.e., exactly when the last reference disappears).

That's all well and good for simple data, but it falls flat on its face with cyclic data. If your data is cyclic, you have to explicitly break it somehow, perhaps via forget, or else no member of the cycle is going to be deallocated. Consider also that if you do this, you also have to be careful that in breaking the cycle you have a (perhaps stack-allocated) smart pointer to yourself as well, or the action of forgetting may trigger a sequence of forgets which eventually causes the method of the object performing the deletion to delete itself! Smart pointers ease much of the common drudgery, but they are not a panacea.

As for the rest of your comment, it's true that having the ability to perform prompt finalization is useful, in some circumstances; it enables idioms like RAII. I do have to disagree with "you can always tell from code inspection exactly when each resource will be acquired and released", however, because determining variable lifetime (particularly effective lifetime, i.e. how long the value of a variable can influence future execution -- GC provides no solution to that problem) for values on the heap can be reduced to the halting problem.

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