implBlog5.ts

// UserModel.ts
type UserModel = { /* ... */ }
namespace UserService {
    function fullName(): string { /* ... */ };
    // ...
}

// HappyBirthdayService.ts
function sendMessage(sessionContext: &SessionContext) {
    let message = happyBirthdayMessage(sessionContext.user);
    sendEmail(user.email, message);
}

function happyBirthdayMessage(user: UserModel) -> String {
    return `Happy Birthday, ${UserService.fullName(user)} 🎉`;
}