convert type []interface {} to type []string

[Tong Sun]

I got "need type assertion" error when trying to convert interface {} array to string array. 

Having looked at the following two answers, 

http://stackoverflow.com/questions/14289256/cannot-convert-data-type-interface-to-type-string-need-type-assertion

http://stackoverflow.com/questions/27244663/cannot-use-temp-type-interface-as-type-string-in-argument-to-equalstringa

I'm still can't get my special case working -- I'm Unmarshaling the following yaml into a `map[interface{}]interface{}` structure:

const data = `

Colors:

  - red

  - blue

  - white

`

m := make(map[interface{}]interface{})

err := yaml.Unmarshal([]byte(data), &m)

The unmarshalled data is apparently some kind of string array. How can tell Go to treat them so? 

The code is kind of long, but I've got the part up to "fmt.Println("\nNext")" working. It is the next two lines I'm struggling to get working. 

Please help. 

PS. Full source code also available at http://pastie.org/10263472

Thanks

package main

import (
	"fmt"
	"os"
	"strings"
	"text/template"

	"gopkg.in/yaml.v2"
)

const data = `
Colors:
  - red
  - blue
  - white
`

const templ1 = `{{range .Colors}}{{.}}, {{end}}`
const templ2 = `{{join .Colors}}`

func main() {

	m := make(map[interface{}]interface{})

	err := yaml.Unmarshal([]byte(data), &m)
	checkError(err)
	fmt.Printf("--- m:\n%v\n\n", m)

	d, err := yaml.Marshal(&m)
	checkError(err)
	fmt.Printf("--- m dump:\n%s\n\n", string(d))

	t := template.New("Test template")
	t, err = t.Parse(templ1)
	checkError(err)

	err = t.Execute(os.Stdout, m)
	checkError(err)

	colors := []string{"red", "white", "blue"}
	t = template.Must(template.New("").Funcs(funcs).Parse(templ2))
	err = t.Execute(os.Stdout, struct{ Colors []string }{colors})
	checkError(err)

	fmt.Println("\nNext")
	fmt.Println(strings.Join(m["Colors"].([]string), ", "))
	err = t.Execute(os.Stdout, struct{ Colors []string }{m["Colors"].([]string)})
	checkError(err)

}

var funcs = template.FuncMap{
	"join": func(s []string) string { return strings.Join(s, ", ") },
}

func checkError(err error) {
	if err != nil {
		fmt.Println("Fatal error ", err.Error())
		os.Exit(1)
	}
}

[Tong Sun]

On Sun, Jun 28, 2015 at 5:46 PM, Tong Sun <sunto...@gmail.com> wrote:

The code is kind of long, but I've got the part up to "fmt.Println("\nNext")" working. It is the next two lines I'm struggling to get working. 

I didn't mean that the custom template function `join` has to keep its interface, I was just trying to show it was working before. What ever will make the next two lines work will do. 

Thanks

[Kiki Sugiaman]

Unfortunately you can only type assert the way you did for interface{}.
For []interface{}, you have to do it element by element.

http://play.golang.org/p/Nq8efe5eWh

[Tamás Gulácsi]

Why can't you unmarshal into a map[string]interface{} ?

[Tong Sun]

That's a good idea. 

Hmm..., on second thought, that wouldn't matter, would it? Because I'll still end up with an interface {} array right? 

On Mon, Jun 29, 2015 at 12:38 AM, Tamás Gulácsi <tgula...@gmail.com> wrote:

Why can't you unmarshal into a map[string]interface{} ?

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