On Sunday, April 30, 2017 at 10:54:07 AM UTC+8, feilengcui008 wrote:
>
> So, if i do this:
> //assign some var to interface type
> var i io.Reader = readerImpl
> i.Read(buf)
>
> the interface i's dynamic type infomation is filled by type deduction in
> compiling phase?
>
yes
>
> also the function table in itab field of interface implementation filling
> with the actually methods of readerImpl also happened in compiling phase?
>
compiler can, but this is done at run time.
>
> if so, this is kind of similar with C++ virtual functions?
>
yes, I think so.
>
>
> 在 2017年4月30日星期日 UTC+8上午3:23:54，T L写道：
>>
>>
>>
>> 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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