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built_in_identifier_in_declaration

Contents

The built-in identifier '{0}' can't be used as a prefix name.

The built-in identifier '{0}' can't be used as a type name.

The built-in identifier '{0}' can't be used as a type parameter name.

The built-in identifier '{0}' can't be used as a typedef name.

The built-in identifier '{0}' can't be used as an extension name.

The built-in identifier '{0}' can't be used as an extension type name.

Description

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The analyzer produces this diagnostic when the name used in the declaration of a class, extension, mixin, typedef, type parameter, or import prefix is a built-in identifier. Built-in identifiers can't be used to name any of these kinds of declarations.

Example

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The following code produces this diagnostic because mixin is a built-in identifier:

dart
extension mixin on int {}

Common fixes

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Choose a different name for the declaration.

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.