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# CFDictionaryHashCallBack

Prototype of a callback function invoked to compute a hash code for a key. Hash codes are used when key-value pairs are accessed, added, or removed from a collection.

```
typealias CFDictionaryHashCallBack = (UnsafeRawPointer?) -> CFHashCode
```

## Parameters

`value`

The value used to compute the hash code.

## Return Value

An integer that can be used as a table address in a hash table structure.

## Discussion

This callback is passed to [`CFDictionaryCreate(_:_:_:_:_:_:)`](/documentation/CoreFoundation/CFDictionaryCreate(_:_:_:_:_:_:)) in a [`CFDictionaryKeyCallBacks`](/documentation/CoreFoundation/CFDictionaryKeyCallBacks) structure.

---

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