map

简介

golang的map主要是基于hash-bucket实现

demoMap:=make(int,len)

type hmap struct {
	// Note: the format of the hmap is also encoded in cmd/compile/internal/reflectdata/reflect.go.
	// Make sure this stays in sync with the compiler's definition.
	count     int // # live cells == size of map.  Must be first (used by len() builtin)
	flags     uint8
	B         uint8  // log_2 of # of buckets (can hold up to loadFactor * 2^B items)
	noverflow uint16 // approximate number of overflow buckets; see incrnoverflow for details
	hash0     uint32 // hash seed

	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) 迁移阶段，下一个桶编号

	extra *mapextra // optional fields
}

其中:
count: 当前map中元素的个数
B: 当前map中bucket的个数
buckets: mapa当前bucket指针
oldbuckets：旧桶指针，存在于桶扩容期间