Get enum value out of function c#

Question

Hey, I have created custom editor field function and I'm trying to get the get enum value out of the function with the "out" keyword. I seem to be all ok with all the different types but I can't seem to get enum out. The function is generic and enum type can be of anything. I'm currently able to get it out by simply changing the return type to Enum but I would like to learn the "out" way too to keep the code consistency all the way same and sometimes I need to return multiple values which "return" doesn't allow instantly.

     Enum EnumTextField(string field, string text , out string textOut, Enum @enum, GUIStyle style)
     {
         GUILayout.BeginHorizontal(field, style);
         textOut = EditorGUILayout.TextField(text);
         @enum= EditorGUILayout.EnumPopup(@enum);
         GUILayout.EndHorizontal();
 
         return @enum;
     }

Simplified the function for easier readability. When I want to use that function I just call:

 NF.enterType = (NodeFollow.TriggerEnterType)EnumTextField("Trigger Name", NF.triggerName, out NF.triggerName, NF.enterType, style);

So, my question is how to get the enum value out with the C# "out" keyword ? ? ? In format like:

 EnumTextField("Trigger Name", NF.triggerName, out NF.triggerName, NF.enterType, out NF.enterType, style);

Answer 1

The function is generic

Uhm, no it's not a generic method. At least not in the sense of generics in C#. You need to actually make a generic method.

Out or ref parameters are kinda restricted when it comes to inheritance. While passing in a more derived variable to a less derived parameter is usually possible, it's not possible for ref or out parameters since the assignment goes the other way round. Inside the method you essentially have a less derived variable. So you could assign any derived type to that variable. However since out parameters are just an alias for the outside variable that would mean you could assign values to the outer variable that it can't hold.

The special Enum type is a bit tricky. Technically an enum is just an integral numeric type (int, byte, ....). Though it's also "derived" from the special struct Enum. There's no real inheritance going on here. The Enum type is just a way to fit the special behaviour of enums into the type system.

As you can read here on SO the latest C# version (7.3+) does now support Enum as a generic constraint. Though it's possible to simply use an unconstraint generic parameter instead. Unfortunately since we currently can not use Enum as generic constraint, we have to actually cast it to object in order to get it to properly cast between Enum and "T". Something like this should work:

 public static void EnumTextField<T>(string field, string text, out string textOut, ref T @enum, GUIStyle style) where T:struct
 {
     GUILayout.BeginHorizontal(field, style);
     textOut = EditorGUILayout.TextField(text);
     @enum = (T)(object)EditorGUILayout.EnumPopup((System.Enum)(object)@enum);
     GUILayout.EndHorizontal();
 }

Note that we have to use a ref parameter instead of an out parameter since you have to read the incoming value for the EnumPopup. out parameters can not be read inside the method since they are only supposed to output a value.

Answer 2

Answer by cdr9042 · Oct 09, 2019 at 10:23 AM

the comment is a bit deep now so I'll write an example of using struct here:

 public struct Damage
 {
     public float value;
     public Type damageType;
     public enum Type { blunt, slash };
 }
 
 
 public class Actor
 {
     public float hp = 500;
 
     public void GetDamageData(out Damage damage)
     {
         damage.value = 10;
         damage.damageType = Damage.Type.blunt;
     }
 }

then you can use them like class. if you manually set all the value, then struct doesn't need to use new () to make an instance

         Actor attacker = new Actor();
         Actor defender = new Actor();
         Damage damageData;
         attacker.GetDamageData(out damageData);
         defender.TakeDamage(damageData);

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Get enum value out of function c#

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