---
title: retain
framework: corefoundation
role: symbol
role_heading: Instance Property
path: corefoundation/cfbagcallbacks/retain
---

# retain

The callback used to retain each value as they are added to the collection. If NULL, values are not retained. See CFBagRetainCallBack for a descriptions of this function’s parameters.

## Declaration

```swift
var retain: CFBagRetainCallBack!
```