Pass by reference, in a method, in a lambda expression

Question

Hi! I have a bit of an issue.

I want to have a method, to create a slider runtime, which sets a referenced value to the slider value.

To do so, I have created a method:

 void CreateSliders(GameObject go)
     {
         GameObject temp = Instantiate(go, holder);
         temp.GetComponentInChildren<Slider>().onValueChanged.AddListener((float f) =>  SaveChange(f));
     }

Now this give me a nice function which should ideally be able to set a referenced value to f, in SaveChange.

Now it looks like this:

 public string s = "0";
     void Awake()
     {
         CreateSliders(sliderFab, ref s);
     }
 
     void CreateSliders(GameObject go, ref string s)
     {
         GameObject temp = Instantiate(go, holder);
         temp.GetComponentInChildren<Slider>().onValueChanged.AddListener((float f) =>  SaveChange(f, ref s));
     }
 
     void SaveChange(float f, ref string s)
     {
         s = f.ToString();
     }

However, this bit of code is illegal, due to the use of s inside the lambda expression. I have tried a lot of things to solve this issue. If I specify the variable inside the function like so:

 public string specified = "0";
     void CreateSliders(GameObject go)
     {
         GameObject temp = Instantiate(go, holder);
         temp.GetComponentInChildren<Slider>().onValueChanged.AddListener((float f) =>  SaveChange(f, ref specified));
     }
 
     void SaveChange(float f, ref string s)
     {
         s = f.ToString();
     }

it works as expected. But then it loses the point, as I would need to specify the referenced variable inside every method. Is there any way to pass a reference to the CreateSlider function, which can be used inside the SaveChange function?

Answer 1

So, after more research I found a work around. Instead of trying to use the ref keyword, I wrapped it in a class, which by default passes by reference, and which a lambda expression has no issue with.

Given in my original code (not exactly like the one shown above) I was already passing a struct, it was quite simple case of adding a new wrapper, and creating a new one inside the struct. this is the final code:

 public class UIPassByReferenceTest : MonoBehaviour
 {
     public Transform holder;
     public GameObject sliderFab, buttonFab;
     public Text t1, t2;
 
     public class wrapper
     {
         public int i;
         public float f;
         public string s;
         public bool b;
     }
 
     public struct pref
     {
         public wrapper wrap;
         public pref(wrapper wrap)
         {
             this.wrap = new wrapper();
         }
     }
 
     wrapper wrap;
     pref a, b;
     void Awake()
     {
         a = new pref(wrap);
         b = new pref(wrap);
         CreateSliders(sliderFab, a);
         CreateSliders(sliderFab, b);
 
     }
 
     void CreateSliders(GameObject go, pref s)
     {
         GameObject temp = Instantiate(go, holder);
         temp.GetComponentInChildren<Slider>().onValueChanged.AddListener((float f) => SaveChange(f, ref s));
     }
 
     void SaveChange(float f, ref pref s)
     {
         s.wrap.s = f.ToString();
     }
     
     private void Update()
     {
         t1.text = a.wrap.s;
         t2.text = b.wrap.s;
     }
 }

And here is how it looks in action alt text

Pass by reference, in a method, in a lambda expression

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