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