Clear mutable semantics or clear immutable semantics but please, don't give us a mushy combination of the two.
In other words, the operation "append to an alias for this slice" should either consistently modify this slice or consistently not modify this slice. Behavior of "sometimes modifies this slice and sometimes doesn't" is, in my opinion, a serious API/language design failure.
In other words, the operation "append to an alias for this slice" should either consistently modify this slice or consistently not modify this slice. Behavior of "sometimes modifies this slice and sometimes doesn't" is, in my opinion, a serious API/language design failure.