delve can't print interface inner member except `data` property

[runningbar]

1. What version of Delve are you using (dlv version)?
   1.2.0

2. What version of Go are you using? (go version)?
   go1.11.6 linux/amd64 and go1.12.1 darwin/amd64

3. What operating system and processor architecture are you using?
   linux/amd64 and darwin/amd64

4. What did you do?
   I want to print interface.tab for iface and interface._type for eface and I failed, however gdb can do the job

5. What did you expect to see?
   see tab and _type value

6. What did you see instead?
   I see this

(dlv) p i.tab
Command failed: i has no member tab

example code

$cat main.go
package main

func main() {
    var a int = 1
    var i interface{}
    i = a
    _ = i
}
$ dlv debug main.go
...
(dlv) p i
interface {}(int) 1
(dlv) p i._type
Command failed: i (type int) is not a struct

I declear i as an interface which underlay is eface type, I want to display the eface member value, but I failed.

[aarzilli]

If you want to see an interface variable as its underlying runtime struct type you have to manually cast to either runtime.iface or runtime.eface:

(dlv) p *((*runtime.eface)(uintptr(&i)))
runtime.eface {
    _type: *runtime._type {
        size: 8,
        ptrdata: 0,
        hash: 4149441018,
        tflag: tflagUncommon|tflagExtraStar|tflagNamed (7),
        align: 8,
        fieldalign: 8,
        kind: 2,
        alg: *(*runtime.typeAlg)(0x4c3050),
        gcdata: *1,
        str: 775,
        ptrToThis: 30080,},
    data: unsafe.Pointer(0xc000038770),}

It's inconvenient but it's also rarely useful compared to having member access autodereference interfaces.

[runningbar]

If you want to see an interface variable as its underlying runtime struct type you have to manually cast to either runtime.iface or runtime.eface:

(dlv) p *((*runtime.eface)(uintptr(&i)))
runtime.eface {
  _type: *runtime._type {
      size: 8,
      ptrdata: 0,
      hash: 4149441018,
      tflag: tflagUncommon|tflagExtraStar|tflagNamed (7),
      align: 8,
      fieldalign: 8,
      kind: 2,
      alg: *(*runtime.typeAlg)(0x4c3050),
      gcdata: *1,
      str: 775,
      ptrToThis: 30080,},
  data: unsafe.Pointer(0xc000038770),}

It's inconvenient but it's also rarely useful compared to having member access autodereference interfaces.

I got it, thank you very very much!