`nonmutating' is not defined （Ice）
说明出处：http://download.zeroc.com/Ice/3.2/IceJ-3.2.1-CHANGES
- ["nonmutating"] provides backward compatibility for idempotent
operations that were previously declared using the deprecated
'nonmutating' keyword. You can replace the 'nonmutating' keyword
with '["nonmutating"] idempotent' to maintain compatibility with
objects implemented using Ice 3.0 or 3.1.
用元数据指令=["nonmutating"]替代关键字nonmutating