/// <summary>
/// Convert an output containing an array to an output containing the length of the array.
/// </summary>
/// <typeparam name="T">The type of elements in the array.</typeparam>
/// <param name="array">An array wrapped into <see cref="Output{T}"/>.</param>
/// <returns>An <see cref="Output{T}"/> containing the array length.</returns>
public static Output <int> Length <T>(this Output <ImmutableArray <T> > array)
=> array.Apply(xs => xs.Length);
public static Output <T1> AsT1 <T0, T1>(this Output <Union <T0, T1> > output) => output.Apply(v => v.AsT1);
public static Output <object> Value <T0, T1>(this Output <Union <T0, T1> > output) => output.Apply(v => v.Value);
public static Output <bool> IsT1 <T0, T1>(this Output <Union <T0, T1> > output) => output.Apply(v => v.IsT1);
