---
title: "subscript(dynamicMember:)"
framework: corevideo
role: symbol
role_heading: Instance Subscript
path: "corevideo/cvattachmentaccess/subscript(dynamicmember:)-1ya6s"
---

# subscript(dynamicMember:)

Get or set composite attachment value as a property of this object.

## Declaration

```swift
subscript<ModePreference, Value>(dynamicMember keyPath: KeyPath<Keys.Type, CVAttachmentCompositeKeyDefinition<ModePreference, Value>>) -> Value? where ModePreference : CVAttachmentModePreference, Value : CVAttachmentValueRepresentable { get set }
```

## Overview

Overview This subscript provides access to an attachment key as a property. The key to be accessed must be defined as a static property on the Keys type. This accessor is intended to be used with legacy keys which are not grouped together in a single container. For new keys, use CVAttachmentKeyDefinitions.Key instead of using a composite key group. enum MyImageTag: CVAttachmentValueRepresentable { 	case int(Int) 	case string(String)

static func makeFromRawAttachmentValue(_ repr: CVAttachmentRawValue) -> Self? { 		guard let kind: String = repr["com.app.MyImageTag.Kind"] else { return nil } 		switch kind { 		case "int": 			guard let value: Int = repr["com.app.MyImageTag.Value"] else { return nil } 			return .int(value) 		case "str": 			guard let value: String = repr["com.app.MyImageTag.Value"] else { return nil } 			return .string(value) 		default: 			return nil 		} 	}

var rawAttachmentValueRepresentation: CVAttachmentRawValue { 		switch self { 		case .int(let value): 			[ 				"com.app.MyImageTag.Kind": "int", 				"com.app.MyImageTag.Value": value, 			] 		case .string(let value): 			[ 				"com.app.MyImageTag.Kind": "str", 				"com.app.MyImageTag.Value": value, 			] 		} 	} }

extension CVPixelBufferAttachmentKeyDefinitions { 	/// A composite key definition which combines legacy top level raw keys 	static var myLegacyImageTag: CompositeKey<ShouldPropagate, MyImageTag> { 		["com.app.MyImageTag.Kind", "com.app.MyImageTag.Value"] 	}

/// For new code, a single key should be used 	static var myImageTag: Key<ShouldPropagate, MyImageTag> { 		"com.app.MyImageTag" 	} }

func inspect(attachments: borrowing CVAttachmentAccess<CVPixelBufferAttachmentKeyDefinitions>) { 	let value1: MyImageTag? = attachments.myLegacyImageTag 	let value2: MyImageTag? = attachments.myImageTag }