On Saturday, April 29, 2017 at 9:56:20 PM UTC+8, feilengcui008 wrote:
>
> Hey, All
>
> I'm curious about what happened when map or slice is assigned to interface
> variables.
>
> I know the interface implementation in go runtime is:
> type iface struct{
> tab *itab
> data unsafe.Pointer
> }
> and the interface static and dynamic type infomation are stored in itab,
> when we use reflect.TypeOf or reflect.ValueOf,
> we can get the dynamic type infomation of this interface.
>
> But it seems that the implementations of slice or map do not have the
> underline element type infomation, here is the map implementation:
> // A header for a Go map.
> type hmap struct {
> 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)
> overflow *[2]*[]*bmap
> }
>
> So when we use reflect.TypeOf or reflect.ValueOf, the map variable will be
> transformed to interface{} and the empty interface will contains the type
> information of the map, how does this happen? where does the interface{}
> get the type information?
>
compiler knows what type the map/slice is.
>
>
> Thanks in advance.
>
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