---
title: "init(type:value:)"
framework: corebluetooth
role: symbol
role_heading: Initializer
path: "corebluetooth/cbmutabledescriptor/init(type:value:)"
---

# init(type:value:)

Creates a mutable descriptor with a specified value.

## Declaration

```swift
init(type UUID: CBUUID, value: Any?)
```

## Parameters

- `UUID`: A 128-bit UUID that identifies the characteristic. You must use only one of the two currently supported descriptor types: doc://com.apple.corebluetooth/documentation/CoreBluetooth/CBUUIDCharacteristicUserDescriptionString or doc://com.apple.corebluetooth/documentation/CoreBluetooth/CBUUIDCharacteristicFormatString. For more details about these descriptor types, see doc://com.apple.corebluetooth/documentation/CoreBluetooth/CBUUID.
- `value`: The descriptor value to cache. You must provide a non-nil value. Once published, you can’t update the value dynamically.

## Return Value

Return Value A newly initialized mutable descriptor.

## Discussion

Discussion The value type of value depends on the type of descriptor: The value type of CBUUIDCharacteristicUserDescriptionString is a string you use to provide a human-readable description of the characteristic’s value. The value type of a CBUUIDCharacteristicFormatString is an NSData object that you use to specify how to format the characteristic’s value for presentation purposes. If you want to create a local characteristic format descriptor, the descriptor’s value must conform to the attribute value of the characteristic format descriptor as defined in the Bluetooth 4.0 specification, Volume 3, Part G, Section 3.3.3.5. For more information, see Core Bluetooth Programming Guide.