API Design: Use type state pattern to avoid ambiguous option flags

For example，ZADD is a command that add member with score to sorted set, and it can accept NX or XX as option.

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ZADD key [NX | XX] [GT | LT] [CH] [INCR] score member [score member
  ...]

• XX: Only update elements that already exist. Don’t add new elements.
• NX: Only add new elements. Don’t update already existing elements. NX 與 XX 只能選一個，在 go-redis 是用這樣的 structure 來裝 argument, 但這就必須要額外的註解與檢查來告訴使用者 NX, XX 是互斥的。

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type ZAddArgs struct {
	NX      bool
	XX      bool
	LT      bool
	GT      bool
	Ch      bool
	Members []Z
}

Ref: go-redis ZAddArgs

但在 redis/rueidis 裡面提供了 command builder, Type System 就會直接禁止你同時設定 NX, XX

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client.B().Zadd().Key("1").Nx().Gt().Ch().Incr().ScoreMember().ScoreMember(1, "1").ScoreMember(1, "1").Build()