Extract values from a map/array object using a key path, e.g. `a[0].b.c[1].d_e.f-g`

extract.go

func ValueAtKeyPath(path string, v interface{}) interface{} {
  // Parse the path syntax
	p := make([]interface{}, 0, len(path))
	rx := regexp.MustCompile(`([a-zA-Z0-9_\-]+)|(\[(\d+)\])`)
	for _, m := range rx.FindAllStringSubmatch(path, -1) {
		if strings.HasPrefix(m[0], "[") {
			i, err := strconv.Atoi(m[len(m)-1])
			if err != nil {
				panic(err)
			}
			p = append(p, i)
		} else {
			p = append(p, m[0])
		}
	}

	// Fetch the object at the parsed path
	obj := v
	for i, k := range p {
		switch tk := k.(type) {
		case int:
			if o, ok := obj.([]interface{}); ok {
				obj = o[tk]
			} else {
				panic(fmt.Sprintf("invalid array key at %d: %s", i, k))
			}
		case string:
			if o, ok := obj.(map[string]interface{}); ok {
				obj = o[tk]
			} else {
				panic(fmt.Sprintf("invalid object key at %d: %s", i, k))
			}
		}
	}
	return obj
}