fun Iterable<Message>.flatten(): Sequence<SingleMessage>
扁平化消息序列.
原 this:
A <- CombinedMessage(B, C) <- D <- MessageChain(E, F, G)
结果 Sequence:
A <- B <- C <- D <- E <- F <- G
@JvmName("flatten1") fun Iterable<SingleMessage>.flatten(): Sequence<SingleMessage>