Firing to Target In Range

I'm creating an arcade game and I created some turrets called "turbolaser". I created a script for these turrets to shoot continously with 1 sec. wait before firing again. No problems occured; here's the script:

 #pragma strict
     
     var shot : GameObject;
     var shotSpawn : Transform;
     var fireRate : float;
     
     private var nextFire : float;
     
     function Update () {
             if (Time.time > nextFire)
             {
                     nextFire = Time.time + fireRate;
                     Instantiate(shot, shotSpawn.position, shotSpawn.rotation);
             }
     }

But then, I tried to stop them from shooting when the player is too far, and configured the script but it didn't work:

 #pragma strict
 
 var shot : GameObject;
 var shotSpawn : Transform;
 var fireRate : float;
 var distance : float;
 var player : Transform;
 var turbolaser : Transform;
 
 private var nextFire : float;
 
 function Update () {
       distance = Vector3.Distance (player - turbolaser);
         if (Time.time > nextFire)
         {
             if(distance <= 20.0f){
                 nextFire = Time.time + fireRate;
                 Instantiate(shot, shotSpawn.position, shotSpawn.rotation);
             }
         }
 }

Then I get this error: Operator "-" cannot be used with a left hand side of type UnityEngine.transform and a right hand side of type UnityEngine.transform.

I understand what the error is telling me, but what should I do ?