Classes can only mix in mixins and classesDRT-W1491

The analyzer produces this diagnostic when a name in a with clause is defined to be something other than a mixin or a class.

Example

The following code produces this diagnostic because F is defined to be a function type:

typedef F = int Function(String);

class C with F {}

Common fixes

Remove the invalid name from the list, possibly replacing it with the name of the intended mixin or class:

typedef F = int Function(String);

class C {}