Println打印方括号，但接口不是切片

Question

I'm having a strange problem with interfaces, when I try to print a value Println adds square brackets. I believe this is because that interface contains slices, but I'm not sure how should iterate them.

I'm quite sure it's a newbie question but I spend alot time searching for a clue and can't find any.

Also I couldn't reproduce it without using goes, so here's the code that I actually used:

package main


import "fmt"
import "github.com/belogik/goes"
import "net/url"

func getConnection() (conn *goes.Connection) {
    conn = goes.NewConnection("localhost", "9200")

    return
}

func main() {

    conn := getConnection()
    var query = map[string]interface{}{
        "query": map[string]interface{}{
            "bool": map[string]interface{}{
                "must": map[string]interface{}{
                    "match_all": map[string]interface{}{},
                },
            },
        },
        "from": 0,
        "size": 3,
        "fields": []string{"name"},
    }
    extraArgs := make(url.Values)
    searchResults, err := conn.Search(query, []string{"myindex"}, []string{"mytype"}, extraArgs)

    if err != nil {
        panic(err)
    }

    result := searchResults.Hits.Hits

    for _,element := range result {
        name := element.Fields["name"]
        fmt.Println( name )
        fmt.Printf( "%#v
", name )
    }
}

This outputs:

[One]
[]interface {}{"One"}
[Two]
[]interface {}{"Two"}
[Three]
[]interface {}{"Three"}

However if I try to loop over the "name" like so:

for _, e := range name {
    fmt.Println( e )
}

I'm getting "cannot range over name (type interface {})"

Answer 1

Use a type assertion. For example,

package main

import "fmt"

func main() {
    m := map[string]interface{}{}
    m["name"] = []interface{}{"One"}
    fmt.Println(m)

    name := m["name"]
    fmt.Println(name)
    fmt.Printf("%#v
", name)

    for _, e := range name.([]interface{}) {
        fmt.Println(e)
    }
}

Output:

map[name:[One]]
[One]
[]interface {}{"One"}
One

The Go Programming Language Specification

Type assertions

For an expression x of interface type and a type T, the primary expression

x.(T)

asserts that x is not nil and that the value stored in x is of type T. The notation x.(T) is called a type assertion.