I am not that familiar with Kotlin, but these seems better than the syntax primitives from a language design perspective (I greatly recommend the “Growing a language” presentation done by Guy Steele), these are ordinary functions that are well-known from other parts of the language, not an added “hack” that has a one-off use. If you were to use a concurrent hashmap implementation you no no longer can use the syntactic sugar, and writing against an implementation is quite common in Java (which plays quite a big role in the design of Kotlin), e.g. having a List in the interface, instead of ArrayList.