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deprecated_subtype_of_function

Contents

Extending 'Function' is deprecated.

Implementing 'Function' has no effect.

Mixing in 'Function' is deprecated.

Description

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The analyzer produces this diagnostic when the class Function is used in either the extends, implements, or with clause of a class or mixin. Using the class Function in this way has no semantic value, so it's effectively dead code.

Example

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The following code produces this diagnostic because Function is used as the superclass of F:

dart
class F extends Function {}

Common fixes

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Remove the class Function from whichever clause it's in, and remove the whole clause if Function is the only type in the clause:

dart
class F {}

Unless stated otherwise, the documentation on this site reflects Dart 3.7.3. Page last updated on 2025-05-08. View source or report an issue.