Copy one struct to another with some uncommon fileds? : I have two structs.

    type UserStruct struct{
        UserID string `bson:"user_id" json:"user_id"`
        Address string `bson:"address" json:"address"`
        Email string `bson:"email" json:"email"`
        CreatedAt time.Time `bson:"created_at" json:"created_at"`
        PhoneNumber string `bson:"phone_number" json:"phone_number"`
        PanCard string `bson:"pancard" json:"pancard"`
        Details map[string]string `json:"details"`
         }

    type SecretsStruct struct {
       UserID string `r:"user_id" json:"user_id"`
       Secrets []string `r:"secrets" json:secrets`
       Address string `r:"address" json:"address"`
       Email string `r:"email"json:"email"`
       CreatedAt time.Time `r:"created_at"json:"created_at"`
       PhoneNumber string `r:"phone_number" json:"phone_number"`
       PanCard string `r:"pancard" json:"pancard"`
     }

I already have all the values in UserStruct, Now I want to copy fields common in both structs, from UserStruct to SecretsStruct without using reflect.  
Things to note:
1) I dont want to use reflections.
