# subscript(_:) Accesses the transaction value associated with a custom key. ``` subscript(key: K.Type) -> K.Value where K : TransactionKey { get set } ``` ## Overview Create custom transaction values by defining a key that conforms to the [`TransactionKey`](/documentation/SwiftUI/TransactionKey) protocol, and then using that key with the subscript operator of the [`Transaction`](/documentation/SwiftUI/Transaction) structure to get and set a value for that key: ``` private struct MyTransactionKey: TransactionKey { static let defaultValue = false } extension Transaction { var myCustomValue: Bool { get { self[MyTransactionKey.self] } set { self[MyTransactionKey.self] = newValue } } } ``` --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)