Cannot modify a value type return value of `UnityEngine.Transform.position'. Can anyone help ?

Question

Hi. When I save t$$anonymous$$s script

 using UnityEngine;
 using System.Collections;
 
 public class Camera_Controll : MonoBehaviour {
 
 float margin = 1.5f; // space between screen border and nearest fighter
  
 private float z0 = 0; // coord z of the fighters plane
 private float zCam; // camera distance to the fighters plane
 private float wScene; // scene width
 private Transform f1; // fighter1 transform
 private Transform f2; // fighter2 transform
 private float xL; // left screen X coordinate
 private float xR; // right screen X coordinate
  
 void  calcScreen ( Transform p1 ,   Transform p2  ){
     // Calculates the xL and xR screen coordinates 
     if (p1.position.x<p2.position.x){
        xL = p1.position.x-margin;
        xR = p2.position.x+margin;
     } else {
        xL = p2.position.x-margin;
        xR = p1.position.x+margin;
     }
 }
  
 void  Start (){
     // find references to the fighters
     f1 = GameObject.Find("Player1").transform;    
     f2 = GameObject.Find("Com").transform;
     // initializes scene size and camera distance
     calcScreen(f1,f2);
     wScene = xR-xL;
     zCam = transform.position.z-z0;
 }
  
 void  Update (){
  
     calcScreen(f1,f2);
     float width = xR-xL;
     if (width>wScene){ // if fighters too far adjust camera distance
        transform.position.z = zCam*width/wScene+z0;
     }
     // centers the camera
     transform.position.x = (xR+xL)/2;
 }
 }

I have error like t$$anonymous$$s

Cannot modify a value type return value of `UnityEngine.Transform.position'. Consider storing the value in a temporary variable

Can anyone help ?

Answer 1

Best Answer

Answer by Owen-Reynolds · Jan 27, 2013 at 03:22 PM

C# has a (stupid) rule that you can only change certain compound variables all at once. The $$anonymous$$nt "Consider storing the value in a temporary variable" is exactly the fix.

Would have been nice if you wrote the line number, but t$$anonymous$$s line: transform.position.z = zCam*width/wScene+z0; is it. You have to assign transform.position all at once. An easy way is:

 Vector3 TP = transform.position; TP.z= ...;  transform.position = TP;

That seems like a giant pain, but in practice, you often want to copy trans.pos into somet$$anonymous$$ng short like TP before using it a lot (and it runs a tiny bit faster.)

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jakobo55 · Jan 27, 2013 at 03:38 PM 0

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Thanks, now I don't have any error but script don't work... I have same script in JS and it work:

 #pragma strict
 
 var margin:float = 1.5; // space between screen border and nearest fighter
  
 private var z0:float = 0; // coord z of the fighters plane
 private var zCam:float; // camera distance to the fighters plane
 private var wScene:float; // scene width
 private var f1:Transform; // fighter1 transform
 private var f2:Transform; // fighter2 transform
 private var xL:float; // left screen X coordinate
 private var xR:float; // right screen X coordinate
  
 function calcScreen(p1:Transform, p2:Transform){
     // Calculates the xL and xR screen coordinates 
     if (p1.position.x<p2.position.x){
        xL = p1.position.x-margin;
        xR = p2.position.x+margin;
     } else {
        xL = p2.position.x-margin;
        xR = p1.position.x+margin;
     }
 }
  
 function Start(){
     // find references to the fighters
     f1 = GameObject.Find("Player1").transform;    
     f2 = GameObject.Find("Com").transform;
     // initializes scene size and camera distance
     calcScreen(f1,f2);
     wScene = xR-xL;
     zCam = transform.position.z-z0;
 }
  
 function Update(){
  
     calcScreen(f1,f2);
     var width:float = xR-xL;
     if (width>wScene){ // if fighters too far adjust camera distance
        transform.position.z = zCam*width/wScene+z0;
     }
     // centers the camera
     transform.position.x = (xR+xL)/2;
 }

But I'm going to write it in C#...

Cannot modify a value type return value of `UnityEngine.Transform.position'. Can anyone help ?

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