Lua环形队列：取余循环的固定容量

local Queue = {}
Queue.__index = Queue
function Queue.new(cap)
    return {buf = {}, cap = cap, head = 1, tail = 1}
end
function Queue.push(q, v)
    if (q.tail % q.cap) + 1 == q.head then
        return false   -- 队满
    end
    q.buf[q.tail] = v
    q.tail = q.tail % q.cap + 1
    return true
end
function Queue.pop(q)
    if q.head == q.tail then return nil end
    local v = q.buf[q.head]
    q.buf[q.head] = nil
    q.head = q.head % q.cap + 1
    return v
end

local q = Queue.new(5)
for i = 1, 5 do q:push(i) end
print(q:push(6))   -- false 队满
print(q:pop())     -- 出队 1
print(q:push(6))   -- true 出队腾位后可入