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extension_declares_constructor

Extensions can't declare constructors.

Description

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The analyzer produces this diagnostic when a constructor declaration is found in an extension. It isn't valid to define a constructor because extensions aren't classes, and it isn't possible to create an instance of an extension.

Example

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The following code produces this diagnostic because there is a constructor declaration in E:

dart
extension E on String {
  E() : super();
}

Common fixes

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Remove the constructor or replace it with a static method.