What flag to fmt.Printf to follow pointers recursively?

Question

I'm having trouble printing a struct when failing test cases. It's a pointer to a slice of pointers to structs, or *[]*X. The problem is that I need to know the contents of the X-structs inside the slice, but I cannot get it to print the whole chain. It only prints their addresses, since it's a pointer. I need it to follow the pointers.

This is however useless since the function I want to test modifies their contents, and modifying the test code to not use pointers just means I'm not testing the code with pointers (so that wouldn't work).

Also, just looping through the slice won't work, since the real function uses reflect and might handle more than one layer of pointers.

Simplified example:

package main

import "fmt"

func main() {
    type X struct {
        desc string
    }

    type test struct {
        in   *[]*X
        want *[]*X
    }

    test1 := test{
        in: &[]*X{
            &X{desc: "first"},
            &X{desc: "second"},
            &X{desc: "third"},
        },
    }

    fmt.Printf("%#v", test1)
}

example output:

main.test{in:(*[]*main.X)(0x10436180), want:(*[]*main.X)(nil)}

(code is at http://play.golang.org/p/q8Its5l_lL )

Answer 1

I don't think fmt.Printf has the functionality you are looking for.

You can use the https://github.com/davecgh/go-spew library.

spew.Dump(test1)

Answer 2

You can use the valast (valast.String()) library alternatively. For the example the out is:

test{in: &[]*X{
    {desc: "first"},
    {desc: "second"},
    {desc: "third"},
}}

For spew (spew.Sdump()) it looks like:

(main.test) {
 in: (*[]*main.X)(0xc000098090)((len=3 cap=3) {
  (*main.X)(0xc000088300)({
   desc: (string) (len=5) "first"
  }),
  (*main.X)(0xc000088310)({
   desc: (string) (len=6) "second"
  }),
  (*main.X)(0xc000088320)({
   desc: (string) (len=5) "third"
  })
 }),
 want: (*[]*main.X)(<nil>)
}