[spockz]

Scala has had this for ages. You can have it today. Even in Java either through the Google collection library or through a library that mimics fp style programming. The name eludes me for the moment.

[gowld]

Guava, but it's not fully typesafe.

Mutable is not part of the Java meta-language used for typing.

ImmutableMap implements Map

https://guava.dev/releases/23.0/api/docs/com/google/common/c...

and throws exceptions on mutation.

https://guava.dev/releases/23.0/api/docs/src-html/com/google...