clientv3/op.go
func OpPut(key, val string, opts ...OpOption) Op {
	ret := Op{t: tPut, key: []byte(key), val: []byte(val)}
	ret.applyOpts(opts)
	switch {
	case ret.end != nil:
		panic("unexpected range in put")
	case ret.limit != 0:
		panic("unexpected limit in put")
	case ret.rev != 0:
		panic("unexpected revision in put")
	case ret.sort != nil:
		panic("unexpected sort in put")
	case ret.serializable:
		panic("unexpected serializable in put")
	case ret.countOnly:
		panic("unexpected countOnly in put")
	case ret.minModRev != 0, ret.maxModRev != 0:
		panic("unexpected mod revision filter in put")
	case ret.minCreateRev != 0, ret.maxCreateRev != 0:
		panic("unexpected create revision filter in put")
	case ret.filterDelete, ret.filterPut:
		panic("unexpected filter in put")
	case ret.createdNotify:
		panic("unexpected createdNotify in put")
	}
	return ret
}
func OpPut(key, val string, opts ...OpOption) Op {
	ret := Op{t: tPut, key: []byte(key), val: []byte(val)}
	ret.applyOpts(opts)
	switch {
	case ret.end != nil:
		panic("unexpected range in put")
	case ret.limit != 0:
		panic("unexpected limit in put")
	case ret.rev != 0:
		panic("unexpected revision in put")
	case ret.sort != nil:
		panic("unexpected sort in put")
	case ret.serializable:
		panic("unexpected serializable in put")
	case ret.countOnly:
		panic("unexpected countOnly in put")
	case ret.minModRev != 0, ret.maxModRev != 0:
		panic("unexpected mod revision filter in put")
	case ret.minCreateRev != 0, ret.maxCreateRev != 0:
		panic("unexpected create revision filter in put")
	case ret.filterDelete, ret.filterPut:
		panic("unexpected filter in put")
	case ret.createdNotify:
		panic("unexpected createdNotify in put")
	}
	return ret
}
// OpPut returns "put" operation based on given key-value and operation options.