RequireComponent.cs

using UnityEngine;
using System;
/// <summary>
/// All scripted behaviour that needs access to internal components should inherit from this.
/// </summary>
public static class ExtensionMethods
{
	/// <summary>
	/// Requires a component from the gameobject currently beeing scripted
	/// without the need for constant use of GetComponent or messy inspectors
	/// using multiple [SerializeField]-attributes.
	/// 
	/// Called in Awake()
	/// </summary>
	public static T RequireComponent<T>(this MonoBehaviour behaviour) where T : Component
	{
		T component = behaviour.GetComponent<T>();
		if(component == null) { component = behaviour.gameObject.AddComponent<T>(); }
		return component;
	}

	/// <summary>
	/// Require a component with a specific setup, e.g. change the component properties
	/// </summary>
	public static T RequireComponent<T>(this MonoBehaviour behaviour, Action<T> setup) where T : Component
	{
		T component = behaviour.GetComponent<T>();
		if(component == null) { component = behaviour.gameObject.AddComponent<T>(); }
		setup(component);
		return component;
	}
}

Usage:

private Rigidbody2D rigid;
private DistanceJoint2D distJoint;

void Awake()
{
    rigid = this.RequireComponent<Rigidbody2D>();
    distJoint = this.RequireComponent(joint => joint.enabled = false));
}

Taking use of the an action as parameter you can simply change properties of the aqquired component, either using lambda expressions or functions. This can be of great use if you need minor changes in the component properties. It can also be used like this:

private Rigidbody2D rigid;
private DistanceJoint2D distJoint;

void Awake()
{
    rigid = this.RequireComponent<Rigidbody2D>();
    distJoint = this.RequireComponent<DistanceJoint2D>(SetupDistanceJoint);
}
stativ void SetupDistanceJoint(DistanceJoint2D distJoint)
{
    distJoint.enabled = false;
    distJoint.enableCollision=true;
    distJoint.distance = 5.0f;
}