Ok, I got that, thanks for the clarification!
在 2017年7月28日星期五 UTC+8上午10:36:20，Matt Harden写道：
>
> Just to be clear, when using unsafe it's possible to do pretty much
> anything; reflect by itself doesn't give you this ability. That's by design
> AIUI.
>
> On Wed, Jul 26, 2017 at 6:53 PM feilengcui008 <feilen...@gmail.com
> <javascript:>> wrote:
>
>> Thanks for your answer :), even though the original question has been
>> deleted.
>>
>> I've used the reflect.NewAt to allocate a new memory at the same address
>> of the unexported field's reflect.Value, it seems work.
>>
>> for unexported not nil field
>>
>> if !v.CanSet() {
>> v = reflect.NewAt(v.Type(), unsafe.Pointer(v.UnsafeAddr())).Elem()
>> }
>>
>>
>> for unexported nil field
>>
>> // since v is nil value, v.Elem() will be zero value
>> // and zero value is not addressable or settable, we
>> // need allocate a new settable v at the same address
>> v = reflect.NewAt(v.Type(), unsafe.Pointer(v.UnsafeAddr())).Elem()
>> newv := reflect.New(v.Type().Elem())
>> v.Set(newv)
>>
>>
>>
>>
>> 在 2017年7月26日星期三 UTC+8上午9:08:50，Ian Lance Taylor写道：
>>
>>> On Sun, Jul 23, 2017 at 12:46 AM, feilengcui008 <feilen...@gmail.com>
>>> wrote:
>>> > Hi, all:
>>> > I'm writing a little fuzz tool for struct using reflect package,
>>> and
>>> > came across the following case, but didn't find any way to solve it
>>> >
>>> >
>>> > type TestStruct struct {
>>> > a *int // unexported nil ptr field, how to modify it?
>>> > b int // unexported not ptr field, can be modified using
>>> > reflect.NewAt
>>> > C *int // exported nil ptr field, can be modified using
>>> > reflect.New and value.Set
>>> > }
>>> >
>>> > ts := &TestStruct {} // a is nil ptr and not exported
>>> > fieldA := reflect.ValueOf(ts).Elem().Field(0)
>>> > // how to modify the value of a using the reflect value fieldA?
>>>
>>> In general you can not use reflect to set unexported fields. If that
>>> were possible, then any package could use reflect to defeat the name
>>> hiding used by any other package, which would make name hiding much
>>> less useful.
>>>
>>> Ian
>>>
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