clientv3/concurrency/stm.go
func (ws writeSet) puts() []v3.Op {
	puts := make([]v3.Op, 0, len(ws))
	for _, v := range ws {
		puts = append(puts, v.op)
	}
	return puts
}
func (ws writeSet) puts() []v3.Op {
	puts := make([]v3.Op, 0, len(ws))
	for _, v := range ws {
		puts = append(puts, v.op)
	}
	return puts
}
// puts is the list of ops for all pending writes