---
title: "CFSetApplyFunction(_:_:_:)"
framework: corefoundation
role: symbol
role_heading: Function
path: "corefoundation/cfsetapplyfunction(_:_:_:)"
---

# CFSetApplyFunction(_:_:_:)

Calls a function once for each value in a set.

## Declaration

```swift
func CFSetApplyFunction(_ theSet: CFSet!, _ applier: ((UnsafeRawPointer?, UnsafeMutableRawPointer?) -> Void)!, _ context: UnsafeMutableRawPointer!)
```

## Parameters

- `theSet`: The set to operate upon.
- `applier`: The callback function to call once for each value in the theSet. If this parameter is not a pointer to a function of the correct prototype, the behavior is undefined. The applier function must be able to work with all values in theSet.
- `context`: A pointer-sized program-defined value, which is passed as the second parameter to the applier function, but is otherwise unused by this function.

## Discussion

Discussion If theSet is mutable, it is unsafe for the applier function to change the contents of the collection.