The class name should self explanatory enough

MonoBehaviourCachedRectTransform.cs

using System;
using UnityEngine;

public class MonoBehaviourCachedRectTransform : MonoBehaviour
{
    [HideInInspector, NonSerialized]
    private RectTransform rectTransform;

    public RectTransform RectTransform
    {
        get { return rectTransform != null ? rectTransform : (rectTransform = GetComponent<RectTransform>()); }
    }
}