Help with trying to change the value of x value of the localScale of a game object with code

Question

Hi there,

I'm trying to create a simple platformer game where I can just move the player game object left or right on the x-axis using the arrow keys on my keyboard. Although I've succeeded in making this functionality work properly through the usage of Rigidbody2D and code, I don't understand a couple of lines of code that I've written and why it works. You can see below in my code I've created a two part if else statement that makes the player sprite image flip depending on which direction the player is moving. Here's the code I've written:

 using System.Collections;
 using System.Collections.Generic;
 using UnityEngine;
  
 public class Player : MonoBehaviour
 {
     private Rigidbody2D _rb;
     public float _moveInput;
     private int _speed = 7;
     public Vector3 _scaler;
     public bool isFacingRight = true;
  
  
     // Start is called before the first frame update
     void Start()
     {
         _rb = GetComponent<Rigidbody2D>();
     }
  
     // Update is called once per frame
     void Update()
     {
         _scaler = transform.localScale;
         _moveInput = Input.GetAxisRaw("Horizontal");
         _rb.velocity = new Vector2(_moveInput * _speed, _rb.velocity.y);
  
  
  
  
         if(isFacingRight == false && _moveInput > 0)
         {
             isFacingRight = true;
            _scaler.x = _scaler.x * -1;
             transform.localScale = _scaler;
             Debug.Log("transform.localScale equals to " + _scaler.x);
  
  
  
         } else if (isFacingRight == true && _moveInput <0)
  
         {
  
             isFacingRight = false;
            _scaler.x = _scaler.x * -1;
             transform.localScale = _scaler;
             Debug.Log("transform.localScale equals to " + _scaler.x);
  
  
         }
      
  
  
     }//update
  
  
  
 }

What I don't understand is if I remove the line "transform.localScale = _scaler;" from the two parts of the if statement the function wont work. I don't understand why it doesn't just work if I just write the if statements with that line removed like so:

 if(isFacingRight == false && _moveInput > 0)
  
         {
             isFacingRight = true;
            _scaler.x = _scaler.x * -1;
             Debug.Log("transform.localScale equals to " + _scaler.x);
  
  
  
         } else if (isFacingRight == true && _moveInput <0)
  
         {
  
             isFacingRight = false;
            _scaler.x = _scaler.x * -1;
             Debug.Log("transform.localScale equals to " + _scaler.x);
  
  
         }

Can anyone explain why I need to include "transform.localScale = _scaler;" in order for the x value of the localScale to change correctly in my if statement?

Answer 1

@segasega89 Your confusion seems to stem from not knowing the difference between reference and value types. localScale, like transform.position, rotation, and others, is a Vector3 struct, and structs are value types. Consider the following:

 int a = 1;
 int _scaler = a;
 _scaler = 2;
 print(a);

You would expect this to print 1, not 2. b was set to the same value as a, and that value was immediately overwritten with the value 2, while a simply stayed the same. Now consider:

 class MyInt {
     public int x;
 }

 MyInt a = new MyInt { Number = 1};
 MyInt _scaler = a;
 _scaler.x= 2;
 print(a.x);

This prints 2. This time you create a new object of type MyInt on the managed heap. The "real" value of a is a pointer to this object, 0x123A56BE or whatever. b is set to the same value, so it now references the same object. Afterwards, you change a value inside that object, and reference it through a.

 struct MyInt {
     public int x;
 }

 MyInt a = new MyInt { Number = 1};
 MyInt _scaler = a;
 _scaler.x= 2;
 print(a.x);

This prints 1. The assignment does the same as in the int example, it copies the whole struct to the "new object" _scaler. Changing a value inside this other object does not change the original object it was copied from.

int, float, string(ish), ulong, byte, char, and every struct are value types, and behave like the first example. Classes behave like the second. I would point you to sets of guidelines, but those are broken as much as they are followed. Immutability of structs for one is not enforced, as you can set _scaler.x. Just know that Vector3 is a struct, and it behaves like int. Other structs in Unity you might encounter are Color, Quaternion, and Scene.

Help with trying to change the value of x value of the localScale of a game object with code

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