I updated Dart random tests. Now reduce should work.

Dart random tests called the solution function with an argument of type List<int>. I changed this type to List<num>. Dart allows List<int> when List<num> is expected because all generic parameters are covariant in Dart and so List<int> is a subtype of List<num>. On the other hand, List<E>.reduce(E combine(E, E)) has a contravariant argument (the return value of combine). That's why it was impossible to use reduce before (all generic arguments of fold are covariant so there were no issues with it).

*Post edited for not being helpful*

I had similar problems when updating versions of some Dart kata. All I can say is that the num being a supertype of int and float, connected with the way how type inference works in Dart, makes things utterly confusing.

I didnt fully grasp how it works, I remmebr that I just sprinkled type annotations and casts to num until I got it working :)

If you check the stack trace, then you can see the error is coming from reduce function itself. So, yes, problem with the code. I don't do Dart, so I don't know why, but adding [...arr] works somehow.

I believe it doesn't work for empty arrays. There is a solution that shows both methods.

We don't know. We don't now what you're logging. Closing.

Thank you for your kindly attention, i've fixed the case. Added the test case for sample and hidden ones.

Read the posts below asking the same.