I agree with you.

Being new to go I wonder why this is considered to be best practice.
Not using the size information when allocating the memory seems like wasteful, no? Growing arrays never comes for free.

Seems the mentioned performance requirements are not that strict..

Thanks

This is awesome

Cool: using toDoubleOrNull instead of catching the exception
Not so much: Two replace passes instead of one with a regex

Upvoted for tailrec <3

This is still O(array1.length * array2.length) - just as yours.
Replacing loops with streams is not taking away complexity.