Style guidelines for allowing implementing interfaces

[pschiffmann]

The Design / types section of the style guide gives recommendations when and how to extend or mixin classes from other packages. However, using implements on a class from another package can also lead to errors, if that package uses is expressions to guard accesses to protected class members.

I just encountered this problem while working with package:built_collection. I want to write a class that implements BuiltSet, but doing that would break this line.

I guess the only way to resolve this is

AVOID implementing a class that isn’t intended to be implemented.

The other option,

DO guard accesses to protected members with a obj.runtimeType == MyClass check

would solve the implements problem, but is unnecessarily restrictive in the extends case.

Best regards,
Philipp

[munificent]

Fixed in 6836e7d.