How to make mixin as sealed class in dart

Question

How I can make mixin class "C" as sealed class cannot be extended outside its library?

class A extends B with C{}
sealed class B{}
mixin class C{}

I don't want C class to be used by a class other than "A" class

Answer 1

There are some tricky ways to accomplish this purpose:

mark your mixin as private mixin as you know (privacy in dart is library level rather than class level) so it can't be used outside it's library.

class A extends B with _C{}
sealed class B{}
mixin class _C{}

another way, you can convert your mixin to sealed class which achieve your purpose also, and implement it (multiple inheritance is not allowed in dart: Diamond Problem)

class A extends B implements C{}
sealed class B{}
sealed class C{}

at last, class C can't be used outside the library in which it's declared, there may still other ways to accomplish your purpose. for more info see Class Modifiers Reference

hope it helps you.