I’d like to discuss the possibility to remove String.plus(Any?)
It is useful in Java for sure, which doesn’t have string interpolation. But in Kotlin, things are different
All that can be accomplished by a+b can be accomplished(more elegantly?) by using "$a$b", especially when a is String? instead of String
It’s more elegant because of the symmetry:
val a=1
val b=""
"$a$b" // consistent
a+b // compile error, though it works in Java
b+a // fine?
Moreover String.plus(Any?) hinders the possibility to define custom plus operator overload
operator fun<T>T.plus(o:Collection<T>)=ArrayList<T>(1+o.size).also{it+=this;it+=o}
This works for all types(including Int) but not String
On the front of source level compatibility, I’d argue that replacing all a+b to "$a$b" is trivial and can easily be automated