can golang function return interface{}{} - how to return a map list

Question

func getLatestTxs() map[string]interface{}{} {
    fmt.Println("hello")
    resp, err := http.Get("http://api.etherscan.io/api?module=account&action=txlist&address=0x266ac31358d773af8278f625c4d4a35648953341&startblock=0&endblock=99999999&sort=asc&apikey=5UUVIZV5581ENPXKYWAUDGQTHI956A56MU")
    defer resp.Body.Close()
    body, _ := ioutil.ReadAll(resp.Body)
    if err != nil {
        fmt.Errorf("etherscan访问失败")
    }
    ret := map[string]interface{}{}
    json.Unmarshal(body, &ret)
    if ret["status"] == 1 {
        return ret["result"]
    }
}

I want return map[string]interface{}{} in my code.

but i got compile error syntax error: unexpected [ after top level declaration

if i change map[string]interface{}{} to interface{}, there is no compile error any more.

Attention i use map[string]interface{}{} because i want return a map list.

for a map list use `[]` in front. e.g. `[]map[string]interface{}`. — mkopriva, Apr 25 '18 at 04:47
@mkopriva if we use `[]map[string]interface{}` it will throw an error. Since `ret["result"]` is an `interface{}` — Himanshu, Apr 25 '18 at 04:57

Charlie Tumahai · Accepted Answer · 2018-04-25T05:33:20.837

The code map[string]interface{}{} is a composite literal value for an empty map. Functions are declared with types, not values. It looks like you want to return the slice type []map[string]interface{}. Use the following function:

func getLatestTxs() []map[string]interface{} {
    fmt.Println("hello")
    resp, err := http.Get("http://api.etherscan.io/api?module=account&action=txlist&address=0x266ac31358d773af8278f625c4d4a35648953341&startblock=0&endblock=99999999&sort=asc&apikey=5UUVIZV5581ENPXKYWAUDGQTHI956A56MU")
    defer resp.Body.Close()
    body, _ := ioutil.ReadAll(resp.Body)
    if err != nil {
        fmt.Errorf("etherscan访问失败")
    }
    var ret struct {
        Status  string
        Result  []map[string]interface{}
    }
    json.Unmarshal(body, &ret)
    if ret.Status == "1" {
        return ret.Result
    }
    return nil
}

i want return a map list, `ret["result"]`, looks you are return a map, That`s right? — 眭文峰, Apr 25 '18 at 04:44

Himanshu · Answer 2 · 2018-04-25T04:58:19.733

Create return type to map[string]interface{}. Because the response returned from GET request is of type map[string]interface{} not map[string]interface{}{} which is a composite literal. So you can use it like

func getLatestTxs() map[string]interface{} {
    fmt.Println("hello")
    // function body code ....
    return ret
}

For this line

if i change map[string]interface{}{} to interface{}, there is no compile error any more.

We can convert anything to interface{} because it works as a wrapper which can wrap any type and will save the underlying type and its value. The value can be received using type assertion for an underlying type. So in your case when you are using an interface it will wrap map[string]interface{} value. For fetching the value it is required to type assert as below.

func getLatestTxs() interface{} {
    fmt.Println("hello")
    // function code .....
    //fmt.Println(ret["result"])
    return ret
}


ret["result"].(interface{}).([]interface{})

print the underlying map[string]interface{} to get the value of single object inside result

fmt.Println(ret["result"].(interface{}).([]interface{})[0].(map[string]interface{})["from"])

`fmt.Println(ret["result"].(interface{}).([]interface{}))` in your case ret["result"] is actually an `interface{}` not `map[string]interface{}` and its innner value is `[]interface{}` slice of interface — Himanshu, Apr 25 '18 at 04:50

can golang function return interface{}{} - how to return a map list

2 Answers2