Go: How to pretty print nested objects with pointers values? [duplicate]

Question

How can I pretty print the object below?

package main

// OBJECT: {
//   TABLE: {
//     files: [],
//     data: {
//        CODE: {
//          name: "NAME",
//          count: 123,
//       }
//     }
//
// }

import (
    "encoding/json"
    "fmt"
    "log"
)

type Container map[string]*Table

type Table struct {
    files []string
    data  map[string]*Data
}

type Data struct {
    name  string
    count int
}

func main() {

    object := Container{
        "table1": {
            files: []string{"file-1.1"},
            data: map[string]*Data{
                "XYZ": {
                    name:  "foo",
                    count: 123,
                },
            },
        },
        "table2": {
            files: []string{
                "file-2.1",
                "file-2.2",
                "file-2.3",
            },
        },
        "table3": {files: []string{"file-3.1"}},
    }

    fmt.Printf("%#v\n", &object)
    objectJSON, err := json.MarshalIndent(object, "", "  ")
    if err != nil {
        log.Fatalf(err.Error())
    }
    fmt.Printf("%s\n", objectJSON)

}

https://go.dev/play/p/FRWZsfwgyNU

With this code, I'm only getting the first depth of my object:

&main.Container{"table1":(*main.Table)(0xc00005c020), "table2":(*main.Table)(0xc00005c040), "table3":(*main.Table)(0xc00005c060)}
{
  "table1": {},
  "table2": {},
  "table3": {}
}

Program exited.

You can have those pointer types implement the Stringer interface. — mkopriva
– mkopriva, Commented May 19, 2022 at 16:39

user229044 · Accepted Answer · 2022-05-19 16:44:27Z

2

This isn't about "depth". You can't generically pretty-print private, un-exported fields using fmt.Printf or json.Marshal. If you want the variable to appear when marshling, export them (ie, change Table.files to Table.Files. Go will marshal exported fields to arbitrary depth:

{
  "foo1": {
    "Files": [
      "file-1.1"
    ],
    "Data": {
      "XYZ": {
        "Name": "foo",
        "Count": 123
      }
    }
  },
  "foo2": {
    "Files": [
      "file-2.1",
      "file-2.2",
      "file-2.3"
    ],
    "Data": null
  },
  "foo3": {
    "Files": [
      "file-3.1"
    ],
    "Data": null
  }
}

If you want to pretty print the object using fmt.Printf("%v", ...) then you need to implement the Stringer interface on each of your class. At that point, the decision about how to print the object is entirely up to you and you can include public or private members in whatever format you'd like.

edited May 19, 2022 at 16:44

answered May 19, 2022 at 16:38

user229044♦

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2 Comments

DevonDahon Over a year ago

Thanks a lot. How come that converting to capital the first letter has so much impact ?

user229044 Over a year ago

Capitalization is visibility.Foo is public. foo is private.

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