---
title: retain
framework: foundation
role: symbol
role_heading: Instance Property
path: foundation/nsmaptablekeycallbacks/retain
---

# retain

Points to the function which increments a reference count for the given element. If NULL, then nothing is done for reference counting.

## Declaration

```swift
var retain: ((NSMapTable<AnyObject, AnyObject>, UnsafeRawPointer) -> Void)?
```