# go get gopkg.in/yaml.v2
# vi test.yml

first: test
secound:
  a1: count1
  a2:
  - count2
  - count3
  a3:
    b1: count4

# vi main.go

package main

import(
  "fmt"
  "io/ioutil"
  "strconv"
  "gopkg.in/yaml.v2"
)

func main() {
  // test.ymlを読み込む
  buf, err := ioutil.ReadFile("test.yml")
  if err != nil {
    fmt.Print("error: Failed to read the file\n")
    return
  }

  // 読み込んだファイルを map[interface {}]interface {}にマッピングする
  t := make(map[interface {}]interface {})
  err = yaml.Unmarshal(buf, &t)
  if err != nil {
    panic(err)
  }

  fmt.Print(t["first"])  // test
  fmt.Print("\n")

  // t["secound"]を(map[interface {}]interface {})で型変換
  fmt.Print(t["secound"].(map[interface {}]interface {})["a1"])  //count1
  fmt.Print("\n")

  // len() 配列の要素数を返す
  fmt.Print(len(t["secound"].(map[interface {}]interface {})))
  fmt.Print("\n")

  // []interface {}型の配列
  fmt.Print(t["secound"].(map[interface {}]interface {})["a2"].([]interface {})[0])  // count2
  fmt.Print("\n")

  fmt.Print(t["secound"].(map[interface {}]interface {})["a3"].(map[interface {}]interface {})["b1"]) // count4
  fmt.Print("\n")

  // 規則的に命名されていれば、いくつあるか確認できる
  flag, i := 0, 0
  for flag == 0 {
    i++
    switch t["secound"].(map[interface {}]interface {})["a"+strconv.Itoa(i)].(type) {
      case nil:
        flag = 1
    }
  }
  fmt.Printf("a%d is not found\n", i)  // a4 is not found
}

# go run main.go
test
count1
3
count2
count4
a4 is not found