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# deallocate

A prototype for a function callback that deallocates a given block of memory. In implementing this function, make the block of memory pointed to by `ptr` available for subsequent reuse by the allocator but unavailable for continued use by the program. The `ptr` parameter cannot be `NULL` and if the `ptr` parameter is not a block of memory that has been previously allocated by the allocator, the results are undefined; abnormal program termination can occur. You can set this callback to `NULL`, in which case the [`CFAllocatorDeallocate(_:_:)`](/documentation/CoreFoundation/CFAllocatorDeallocate(_:_:)) function has no effect.

```
var deallocate: CFAllocatorDeallocateCallBack!
```

---

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