Question

Assuming the following domain entity :

public enum Role
{
    User = 0,
    Moderator = 1,
    Administrator = 2
}

public class User
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }
    public Role Role { get; set; }
}

I need to know if the user can perform “Edit” action. So i’ve 2 solutions :

Create a CanEdit method inside the User entity

public class User
{
    public string FirstName { get; set; }
    public string LastName { get; set; }
    public string Email { get; set; }
    public Role Role { get; set; }

    public bool CanEdit()
    {
        return Role == Role.Moderator || Role == Role.Administrator;
    }
}

Create a CanEdit Extension Method for User type :

public static class UserExtensions
{
    public static bool CanEdit(this User user)
    {
        return user.Role == Role.Moderator || user.Role == Role.Administrator;
    }
}

Both solution works, but the question is WHEN use standard methods vs using Extensions methods ?

Answer 1

Extension methods are simply syntactic sugar for plain, ordinary static methods.

If you control the class structure, you should implement all the necessary functionality within the class. Where extension methods are really useful/necessary is if you don’t own the class that you are trying to “extend.”

For this example, I think you should put the logic inside the User class. It is a logical function of the user itself; consumers should be able to use the CanEdit() method without having to use or even know about the UserExtensions class.