LaserScript.cs

using UnityEngine;
using System.Collections;

public class LaserScript : MonoBehaviour
{
  [Header("Laser pieces")]
  public GameObject laserStart;
  public GameObject laserMiddle;
  public GameObject laserEnd;

  private GameObject start;
  private GameObject middle;
  private GameObject end;

  void Update()
  {
    // Create the laser start from the prefab
    if (start == null)
    {
      start = Instantiate(laserStart) as GameObject;
      start.transform.parent = this.transform;
      start.transform.localPosition = Vector2.zero;
    }

    // Laser middle
    if (middle == null)
    {
      middle = Instantiate(laserMiddle) as GameObject;
      middle.transform.parent = this.transform;
      middle.transform.localPosition = Vector2.zero;
    }

    // Define an "infinite" size, not too big but enough to go off screen
    float maxLaserSize = 20f;
    float currentLaserSize = maxLaserSize;

    // Raycast at the right as our sprite has been design for that
    Vector2 laserDirection = this.transform.right;
    RaycastHit2D hit = Physics2D.Raycast(this.transform.position, laserDirection, maxLaserSize);

    if (hit.collider != null)
    {
      // We touched something!

      // -- Get the laser length
      currentLaserSize = Vector2.Distance(hit.point, this.transform.position);

      // -- Create the end sprite
      if (end == null)
      {
        end = Instantiate(laserEnd) as GameObject;
        end.transform.parent = this.transform;
        end.transform.localPosition = Vector2.zero;
      }
    }
    else
    {
      // Nothing hit
      // -- No more end
      if (end != null) Destroy(end);
    }

    // Place things
    // -- Gather some data
    float startSpriteWidth = start.renderer.bounds.size.x;
    float endSpriteWidth = 0f;
    if (end != null) endSpriteWidth = end.renderer.bounds.size.x;

    // -- the middle is after start and, as it has a center pivot, have a size of half the laser (minus start and end)
    middle.transform.localScale = new Vector3(currentLaserSize - startSpriteWidth, middle.transform.localScale.y, middle.transform.localScale.z);
    middle.transform.localPosition = new Vector2((currentLaserSize/2f), 0f);

    // End?
    if (end != null)
    {
      end.transform.localPosition = new Vector2(currentLaserSize, 0f);
    }

  }
}