Still not sure how GetComponent works

using UnityEngine;
using System.Collections;

public class WheelSuspension : MonoBehaviour {

public GameObject other;
public Rigidbody rb = GetComponent<Rigidbody>();
public float thrust = 20f;

void OnTriggerStay()
{
rb.AddForce(-transform.up * thrust);
}
}

This is my code to add a force to wheels and create suspension because I don't want the wheels to rub against the car body. When I try to play the game it gives me this error:
Assets/WheelSuspension.cs(7,27): error CS0236: A field initializer cannot reference the nonstatic field, method, or property `UnityEngine.Component.GetComponent(System.Type)'
Would somebody be able to help me with this and clarify GetComponent for me?

 

youll have to do it elsewhere for example in Start

Code (CSharp):

1. public Rigidbody rb;
2. void Start()
3. {
4. rb=GetComponent<Rigidbody>();
5. }

 

When you call GetComponent where you did there, it's called before the constructor for that class is run. Now in this case, Unity is handling the constructor and creation of the game object and its components. Unity needs to be able to fully create the object and its components before allowing you to use GetComponent. The start and awake methods give you a place to write code after the object has been fully created, making jaasso's answer correct.

 

Thank you!