title: I keep getting exception Feature `interpolated strings' cannot be used because it is not part of the C# 4.0 language?
body: <p>First I had the exception the error in the visual studio.
  So I clicked on the line with the error and selected to fix it to change the visual studio target to csharp 6</p>
  
  <pre><code>using System.Collections;
  using System.Collections.Generic;
  using System.IO;
  using System.Linq;
  using UnityEditor;
  using UnityEngine;
  
  public class PrefabReplace : EditorWindow
  {
      [SerializeField] private GameObject prefab;
  
      [MenuItem("Tools/Prefab Replace")]
      static void CreateReplaceWithPrefab()
      {
          EditorWindow.GetWindow&lt;PrefabReplace&gt;();
      }
  
      private void OnGUI()
      {
          prefab = (GameObject)EditorGUILayout.ObjectField("Prefab", prefab, typeof(GameObject), false);
  
          if (GUILayout.Button("Replace"))
          {
              var selection = Selection.gameObjects.ToList();
  
              if (prefab != null &amp;&amp; selection.Count &gt; 0)
              {
                  for (var i = selection.Count - 1; i &gt;= 0; --i)
                  {
                      var selected = selection[i];
                      var prefabType = PrefabUtility.GetPrefabType(prefab);
                      GameObject newObject;
  
                      if (prefabType == PrefabType.Prefab)
                      {
                          newObject = (GameObject)PrefabUtility.InstantiatePrefab(prefab);
                      }
                      else
                      {
                          newObject = Instantiate(prefab);
                          newObject.name = prefab.name;
                      }
  
                      if (newObject == null)
                      {
                          Debug.LogError("Error instantiating prefab");
                          break;
                      }
  
                      Undo.RegisterCreatedObjectUndo(newObject, "Replace With Prefabs");
                      newObject.transform.parent = selected.transform.parent;
                      newObject.transform.localPosition = selected.transform.localPosition;
                      newObject.transform.localRotation = selected.transform.localRotation;
                      newObject.transform.localScale = selected.transform.localScale;
                      newObject.transform.SetSiblingIndex(selected.transform.GetSiblingIndex());
                      Undo.DestroyObjectImmediate(selected);
                  }
              }
          }
  
          if (GUILayout.Button("Copy settings"))
          {
              var selection = Selection.gameObjects.ToList();
  
              for (int i = selection.Count - 1; i &gt;= 0; --i)
              {
                  var selected = selection[i].transform;
                  string toWrite = $"{selected.parent}:{selected.localPosition}:{selected.localRotation}:{selected.localScale}";
                  WriteDataToFile(toWrite);
              }
          }
  
          GUI.enabled = false;
          EditorGUILayout.LabelField("Selection count: " + Selection.objects.Length);
      }
  
      private void OnInspectorUpdate()
      {
          Repaint();
      }
  
      private void WriteDataToFile(string line)
      {
          string path = "Assets/Resources/test.txt";
          string[] text = new string[4];
          if (File.Exists(path))
          {
              text = File.ReadAllLines(path);
              if (!text.Contains(line))
                  File.AppendAllText(path, line);
          }
      }
  }
  </code></pre>
  
  <p>The error was on this line in the visual studio:</p>
  
  <pre><code>string toWrite = $"{selected.parent}:{selected.localPosition}:{selected.localRotation}:{selected.localScale}";
                  WriteDataToFile(toWrite);
  </code></pre>
  
  <p>Now the error is gone from the visual studio and I can build it without any problems but in the unity editor the exception still exist in the console and clicking on the Clear button not removing it:</p>
  
  <p><a href="https://i.stack.imgur.com/9HtKl.jpg" rel="noreferrer"><img src="https://i.stack.imgur.com/9HtKl.jpg" alt="Exception in editor"></a></p>