Question

A fairly basic problem for a change. Given a class such as this:

public class X
{
    public T A;
    public T B;
    public T C;
    ...

    // (other fields, properties, and methods are not of interest here)
}

I am looking for a concise way to code a method that will return all A, B, C, ... that are not null in an enumerable collection. (Assume that declaring these fields as an array is not an option.)

public IEnumerable<T> GetAllNonNullABCs(this X x)
{
    // ?
}

The obvious implementation of this method would be:

public IEnumerable<T> GetAllNonNullABCs(this X x)
{
    var resultSet = new List<T>();

    if (x.A != null) resultSet.Add(x.A);
    if (x.B != null) resultSet.Add(x.B);
    if (x.C != null) resultSet.Add(x.C);
    ...

    return resultSet;
}

What’s bothering me here in particular is that the code looks verbose and repetitive, and that I don’t know the initial List capacity in advance.

It’s my hope that there is a more clever way, probably something involving the ?? operator? Any ideas?

---

Note about the chosen answer:

I finally went for a mix of both Bryan Watts’ and dtb’s answers that allows for a clear separation of defining the set of properties A,B,C,... and the filtering of the non-null subset:

(1) Definition of the set of included fields/properties:

IEnumerable<T> AllABCs(this X x)
{
    return new[] { x.A, x.B, x.C, ... };
}

Or alternatively:

IEnumerable<T> AllABCs(this X x)
{
    yield return x.A;
    yield return x.B;
    yield return x.C;
    ...
    yield break;
}

(2) Returning only non-null values:

IEnumerable<T> ThatAreNotNull(this IEnumerable<T> enumerable)
{
    return enumerable.Where(item => item != null);
}

IEnumerable<T> AllNonNullABCs(this X x)
{
    return AllABCs().ThatAreNotNull();
    //     ^^^^^^^^^^^^^^^^^^^^^^^^^^
    //     goal reached; it won't get shorter and clearer than this, IMO!
}

Answer 1

public static IEnumerable<T> GetAllNonNullAs(this X x)
{
    return new[] { x.A, x.B, x.C }.Where(t => t != null);
}