Generic way to format object as subject and body?

Question

I am trying to take a list of objects and format these as an email subject and body. To illustrate what I am doing, take the following examples: ``` public string GetSubject(Person myPerson) { return String.Format("To {0}", myPerson.Name); } public string GetMessage(Person myPerson) { return String.Format("Dear {0}, Your new salary: {1}", myPerson.Name, myPerson.Salary); } public string GetSubject(VacationDay dayOff) { return String.Format("Vacation reminder!"); } public string GetMessage(VacationDay dayOff) { return String.Format("Reminder: this {0} is a vacation day!", dayOff.Name); } ``` Later I have a bunch of emails which I want to send in a batch: ``` // myEmailObjects is a "List<object>" foreach (var emailItem in myEmailObjects) { SendEmail(from, to, GetSubject(emailItem), GetMessage(emailItem)); } ``` The problem is this code doesn't compile because the compiler can't resolve which `GetSubject` and which `GetMessage` routine to call. Is there any generic way to write this with…

Accepted Answer

This is what interfaces are made for. Conceptually, an interface is like a contract that a class can sign where it obliges to define the methods that the interface specifies. Define each of the `GetSubject()` and `GetMessage()` methods as member methods of the corresponding classes instead, and then create the following interface:

```
public interface IEmailable {
    string GetSubject();
    string GetMessage();
}
```

Then, make all of the involved classes implement the interface:

```
public class VacationDay : IEmailable
```

You can now create a `List<IEmailable>()`, and you may call those two methods on its elements.

Generic way to format object as subject and body?

Solution

Problem