How to parse JSON array in Go

Note: This answer was written before the question was edited. In the original question &arr was passed to json.Unmarshal():

unmarshaled := json.Unmarshal([]byte(dataJson), &arr)

---

You pass the address of arr to json.Unmarshal() to unmarshal a JSON array, but arr is not an array (or slice), it is a struct value.

Arrays can be unmarshaled into Go arrays or slices. So pass arr.Array:

dataJson := `["1","2","3"]`
arr := JsonType{}
err := json.Unmarshal([]byte(dataJson), &arr.Array)
log.Printf("Unmarshaled: %v, error: %v", arr.Array, err)

Output (try it on the Go Playground):

2009/11/10 23:00:00 Unmarshaled: [1 2 3], error: <nil>

Of course you don't even need the JsonType wrapper, just use a simple []string slice:

dataJson := `["1","2","3"]`
var s []string
err := json.Unmarshal([]byte(dataJson), &s)

The return value of Unmarshal is an error, and this is what you are printing out:

// Return value type of Unmarshal is error.
err := json.Unmarshal([]byte(dataJson), &arr)

You can get rid of the JsonType as well and just use a slice:

package main

import (
    "encoding/json"
    "log"
)

func main() {
    dataJson := `["1","2","3"]`
    var arr []string
    _ = json.Unmarshal([]byte(dataJson), &arr)
    log.Printf("Unmarshaled: %v", arr)
}

// prints out:
// 2009/11/10 23:00:00 Unmarshaled: [1 2 3]

Code on play: https://play.golang.org/p/GNWlylavam

Background: Passing in a pointer allows Unmarshal to reduce (or get entirely rid of) memory allocations. Also, in a processing context, the caller may reuse the same value to repeatedly - saving allocations as well.