Access the x, y, z, w components using [0], [1], [2], [3] respectively.
var p : Vector4; p[3] = 5; // the same as p.w = 5
using UnityEngine; using System.Collections; public class Example : MonoBehaviour { public Vector4 p; void Example() { p[3] = 5; } }
import UnityEngine import System.Collections public class Example(MonoBehaviour): public p as Vector4 def Example() as void: p[3] = 5