load config from env

load_config.go

package main

import "reflect"

func loadConfig(data interface{}) {
	v := reflect.ValueOf(data)
	if v.Kind() != reflect.Ptr || v.Type().Elem().Kind() != reflect.Struct {
		panic("expected a pointer to a struct")
	}

	ve := v.Elem()
	vt := ve.Type()

	for i := 0; i < vt.NumField(); i++ {
		ft := vt.Field(i)

		envName := ft.Tag.Get("env")
		if envName == "" {
			continue
		}

		envValue := os.Getenv(envName)
		if envValue == "" {
			continue
		}

		fv := ve.Field(i)
		switch ft.Type.Kind() {
		case reflect.String:
			fv.SetString(envValue)
		}
	}
}