# subscript(_:) Accesses the environment value associated with a custom key. ``` subscript(key: K.Type) -> K.Value where K : EnvironmentKey { get set } ``` ## Overview Create a custom environment value by declaring a new property in an extension to the environment values structure and applying the [`Entry()`](/documentation/SwiftUI/Entry()) macro to the variable declaration: ``` extension EnvironmentValues { @Entry var myCustomValue: String = "Default value" } ``` You use custom environment values the same way you use system-provided values, setting a value with the [`environment(_:_:)`](/documentation/SwiftUI/View/environment(_:_:)) view modifier, and reading values with the [`Environment`](/documentation/SwiftUI/Environment) property wrapper. You can also provide a dedicated view modifier as a convenience for setting the value: ``` extension View { func myCustomValue(_ myCustomValue: String) -> some View { environment(\.myCustomValue, myCustomValue) } } ``` --- 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)