1. type hmap struct {
    2.    count        int  //元素个数
    3.    flags        uint8  
    4.    B            uint8 //扩容常量
    5.    noverflow    uint16 //溢出 bucket 个数
    6.    hash0        uint32 //hash 种子
    7.    buckets      unsafe.Pointer //bucket 数组指针
    8.    oldbuckets   unsafe.Pointer //扩容时旧的buckets 数组指针
    9.    nevacuate    uintptr  //扩容搬迁进度
    10.    extra        *mapextra //记录溢出相关
    11. }
    1. type bmap struct {
    2.    tophash        [bucketCnt]uint8  
    3.    // Followed by bucketCnt keys
    4.    //and then bucketan Cnt values  
    5.    // Followed by overflow pointer.
    6. }