How do I get an object to move and swap places with another object, on a mouse clic

Question

I have a script so far that moves an object a small distance upon a mouse click, however I want to change it so that when I click this object, it swaps places with another obejct next to it, instead of just the small distance it is moving now. I am a little confused on how to do this, because I am new to unity.

 using UnityEngine;
 using System.Collections;

 public class NewBehaviourScript: MonoBehaviour
 {
     public float movementSpeed = 10;

     void Update(){
         if ( Input.GetMouseButtonDown(0))
         {
             transform.Translate(Vector3.right * movementSpeed * Time.deltaTime);
         }


     }
 }

Answer 1

Try this:

 using UnityEngine;
 using System.Collections;

 public class NewBehaviourScript: MonoBehaviour {
     public GameObject objectA; //Needs to be initialized in the editor, or on Start
     public GameObject objectB; //Needs to be initialized in the editor, or on Start
     public float movementSpeed = 10;
     private Vector3 posA = Vector3.zero; //Vector3.zero is for initialization
     private Vector3 posB = Vector3.zero; //Vector3.zero is for initialization

     void Update() {
         if ( Input.GetMouseButtonDown(0)) {
             posA = objectA.gameObject.transform.position;
             posB = objectB.gameObject.transform.position;
             objectA.gameObject.transform.position = posB;
             objectB.gameObject.transform.position = posA;
         }
     }

 }

This just saves each objects position into the posA and posB variables, then you move objectA to posB and objectB to posA.

-OR-

Now if objectB is always a different object (NOT constant) and you aren't sure how to find the nearest object, you could use a raycast. Add the following function to your code:

gamObject NearestObject () {
    int dist;
    int nearestIndex;
    //Create an array to contain objects to be hit by the raycast
    RaycastHit[] nearby;
    //Hit all objects within 100 units with a raycast, change the 100 as needed
    nearby = Physics.RaycastAll(objectA.transform.position, transform.forward, 100.0f);
    //Check if there is at least one object
    if(nearby.Length > 0) {
        //If there is only one object and it's not objectA
        if(!(nearby.Length == 1 && nearby[0].transform == objectA.transform)) {
            dist = nearby[0].distance;
            nearestIndex = 0;
            for (int i = 1; i < nearby.Length; i++) {
                if(nearby[i].transform != gameObject.transform && nearby[i].distance < dist)
                    dist = nearby[i].distance;
                    nearestIndex = i;
                }
            }
        } else {
           //There is only one object in the raycast and it is objectA
           nearestIndex = -1; 
        }
    } else {
        //There are no objects nearby
        nearestIndex = -1;
    }
    //nearestIndex will only be negative one if there are no objects near objectA, so return null
    if (nearestIndex == -1) {
        return null;
    } else {
        //return nearest object to update
        return nearby[nearestIndex].gameObject;
    }
}

Finally, change Update to:

     void Update() {
         if ( Input.GetMouseButtonDown(0)) {
             objectB = NearestObject ();
             if (objectB != null) {
                 posA = objectA.gameObject.transform.position;
                 posB = objectB.gameObject.transform.position;
                 objectA.gameObject.transform.position = posB;
                 objectB.gameObject.transform.position = posA;
             }
         }
     }