assert-interface-in-map.go

package main

import (
	"errors"
	"fmt"
	"time"
)

func main() {
	check(extractTime(nil))
	check(extractTime(makeFields()))
}

func check(t time.Time, err error) {
	if err != nil {
		fmt.Println("Can't find time", err)
	} else {
		fmt.Printf("Time %v\n", t)
	}
}

func extractTime(fields map[string]interface{}) (time.Time, error) {
	timeField, ok := fields["time"].(string)
	if !ok {
		return time.Time{}, errors.New("Can't find time field")
	}
	return time.Parse(time.RFC3339, timeField)
}

func makeFields() map[string]interface{} {
	m := make(map[string]interface{})
	m["time"] = time.Now().UTC().Format(time.RFC3339)
	return m
}