Function overloading with and optional arguments

Question

Hi folk. I need your help. Can you explain script behaviour?

There is a test project with one button and one script.

script:

 using UnityEngine;
 using System;
 
 public class TestScript : MonoBehaviour {
   private void TestFunc(object value, Action action = null) {
     Debug.Log("Single");
   }
 
   private void TestFunc(object[] value, Action action = null) {
     Debug.Log("Array");
   }
 
   public void OnClick() {
     object single = new object();
     this.TestFunc(single); // <-- All good
 
     object[] array = new object[] { };
     this.TestFunc(array); // <-- Error is here
   }
 }

MS VS 2016 doesn't show any errors.

But I received error in Unity:

Assets/TestScript.cs(18,10): error CS0121: The call is ambiguous between the following methods or properties: 'TestScript.TestFunc(object, System.Action)' and 'TestScript.TestFunc(object[], System.Action)'

PS: sorry for my English

PPS: this is compiler bug

I'm glad to inform that we have fixed this and will be released with the new version of our compiler (on Unity 5.5)

Answer 1

Best Answer

Answer by btmedia14 · Jun 17, 2016 at 05:41 PM

The first function with the single Object signature

 private void TestFunc(object value, Action action = null)

allows the function to to be called with any object as the first parameter. Object is the base class for everything in Unity. As such it will accept arrays of objects or any other datatypes derived from Object. An array of Objects is just another Object. However, in the case of Object[] as a parameter, the compiler also happens to pattern match against the second method signature. Hence the ambiguity. If the datatypes were other than Object, say int, the method signatures would be considered unique enough when being called with an array of ints.

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Don-Fear · Jun 20, 2016 at 06:27 AM 0

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But why in case of

 private void TestFunc(object value)

and

 private void TestFunc(object[] value)

There are no errors?

btmedia14 Don-Fear · Jun 21, 2016 at 02:15 AM 0

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That is interesting. There should be compile time errors in both sets of signatures. I checked under Visual Studio 2015 as well as $$anonymous$$onoDevelop and do see compiler errors of the type you listed earlier in both cases. For Visual Studio ensure the error filter within the Error List window is not suppressed else no errors will be listed even though errors are generated.

Don-Fear btmedia14 · Jun 21, 2016 at 06:36 AM 0

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Here is screen with both situations. And i have only one error message only in unity. Both situations. New Code alt text Interesting! If I reload Unity, without change any code in VS, I have NO errors in Unity and I can run project. But executed only "single" version of "TestFunc_1" After Unity reloading If I change any code in VS, i receive same Unity error.