Question

Is it possible to enforce rules or throw an error when using object initializers in C#? I’d like to throw a compiler error or warning if an object is initialized but is missing a certain property.

public class Party
{
    public string Name { get; set; }
    public string Date { get; set; }
    public Location Location { get; set; }
}

public class SignUpForParty
{
    public void DoSomething()
    {
        Party party = new Party()
        {
            Name = "New Years Party!",
            Date = "Dec 31, 1999"
            // Show WARNING/ERROR here because no Location given
        };
    }
}

Essentially, I’m looking for a way to ensure that all objects of type Party are created with valid data for every instance.

Obviously I could do this with overloaded constructors, but in some cases I have a lot of properties and writing constructors to match is messy. I’d like to follow a cleaner C# style.

Obj p = new Obj(1, 2, 3,...n); // too many properties to be pretty

Answer 1

Obviously I could do this with overloaded constructors, but in some cases I have a lot of properties and writing constructors to match is messy. I’d like to follow a cleaner C# style.

Object initializers really shouldn’t be considered alternatives to writing a constructor.

You should always include constructors in your types if you have requirements like this. It is a good idea to create a default set of constructors (or use optional arguments on one constructor) which at least provide a guarantee that the object will always be created in a valid, meaningful state.

Object initializers are helpful for optional properties, but shouldn’t be relied upon for requirements of your type itself.