Type variance

[KeenS]

In client, strings at arguments should be &str and those in return value should be String, and in server, vice versa.

open issue

In server, how to settle the lifetime of return value? fn foo(&self, arg: String) -> &str will inferred to fn foo<'a>(&'a str, arg: String) -> &'a str. Is this correct (usable) ?.