这是地图标题的定义：
// A header for a Go map.type hmap struct { // Note: the format of the Hmap is enpred in ../../cmd/gc/reflect.c and // ../reflect/type.go. Don't change this structure without also changing that pre! count int // # live cells == size of map. Must be first (used by len() builtin) flags uint32 hash0 uint32 // hash seed B uint8 // log_2 of # of buckets (can hold up to loadFactor * 2^B items) buckets unsafe.Pointer // array of 2^B Buckets. may be nil if count==0. oldbuckets unsafe.Pointer // previous bucket array of half the size, non-nil only when growing nevacuate uintptr // progress counter for evacuation (buckets less than this have been evacuated)}计算其大小非常简单（unsafe.Sizeof）。
这是地图指向的每个单独存储区的定义：
// A bucket for a Go map.type bmap struct { tophash [bucketCnt]uint8 // Followed by bucketCnt keys and then bucketCnt values. // NOTE: packing all the keys together and then all the values together makes the // pre a bit more complicated than alternating key/value/key/value/... but it allows // us to eliminate padding which would be needed for, e.g., map[int64]int8. // Followed by an overflow pointer.}bucketCnt是一个常量，定义为：
bucketCnt = 1 << bucketCntBits // equals decimal 8bucketCntBits = 3
最终计算将为：
unsafe.Sizeof(hmap) + (len(theMap) * 8) + (len(theMap) * 8 * unsafe.Sizeof(x)) + (len(theMap) * 8 * unsafe.Sizeof(y))
theMap地图值在哪里，
x是地图键类型
y的值和地图值类型的值。
hmap与
thunk.s运行时类似，您必须通过组装与包共享结构。
