public abstract class CIMVisualVariable : CIMObject, System.ComponentModel.INotifyPropertyChanged, System.Xml.Serialization.IXmlSerializable  

{
  //Consult https://github.com/Esri/arcade-expressions/ and
  //https://developers.arcgis.com/arcade/ for more examples
  //and arcade reference

  // Note: the following should be embedded in a QueuedTask.Run() statement
  {
    //Assume we have a layer that is using Visual Variable
    //expressions that we want to evaluate interactively...
    var def = featureLayer.GetDefinition() as CIMFeatureLayer;

    //Most all feature renderers have a VisualVariable collection
    var renderer = def.Renderer as CIMUniqueValueRenderer;
    List<CIMVisualVariable> vis_variables = renderer.VisualVariables?.ToList() ??
                          [];
    if (vis_variables.Count == 0)
      return;//there are none
    var vis_var_with_expr = new Dictionary<string, string>();
    //see if any are using expressions
    foreach (var vv in vis_variables)
    {
      if (vv is CIMColorVisualVariable cvv)
      {
        if (!string.IsNullOrEmpty(cvv.ValueExpressionInfo?.Expression))
          vis_var_with_expr.Add("Color", cvv.ValueExpressionInfo?.Expression);
      }
      else if (vv is CIMTransparencyVisualVariable tvv)
      {
        if (!string.IsNullOrEmpty(tvv.ValueExpressionInfo?.Expression))
          vis_var_with_expr.Add("Transparency", tvv.ValueExpressionInfo?.Expression);
      }
      else if (vv is CIMSizeVisualVariable svv)
      {
        if (!string.IsNullOrEmpty(svv.ValueExpressionInfo?.Expression))
          vis_var_with_expr.Add("Outline", svv.ValueExpressionInfo?.Expression);
      }
    }
    if (vis_var_with_expr.Count == 0)
      return;//there aren't any with expressions

    //loop through the features (outer)
    //per feature evaluate each visual variable.... (inner)
    //....
    //the converse is to loop through the expressions (outer)
    //then per feature evaluate the expression (inner)
    using RowCursor rc = featureLayer.Search();
    while (rc.MoveNext())
    {
      foreach (var kvp in vis_var_with_expr)
      {
        var expr_info = new CIMExpressionInfo()
        {
          Expression = kvp.Value,
          ReturnType = ExpressionReturnType.Default
        };
        //per feature eval each expression...
        using ArcadeEvaluator arcade = ArcadeScriptEngine.Instance.CreateEvaluator(
                                    expr_info, ArcadeProfile.Visualization);

        var variables = new List<KeyValuePair<string, object>>() {
            new("$feature", rc.Current)
          };
        //note 2D maps can also have view scale...
        //...if necessary...
        if (mv.ViewingMode == MapViewingMode.Map)
        {
          variables.Add(new("$view.scale", mv.Camera.Scale));
        }
        var result = arcade.Evaluate(variables).GetResult().ToString();
        //output
        System.Diagnostics.Debug.WriteLine(
           $"[{rc.Current.GetObjectID()}] '{kvp.Key}': {result}");
      }
    }
  }
}

/// <summary>
/// Renders a feature layer using graduated colors to draw quantities. The outline width is varied based on attributes.
/// ![graduatedColorOutline.png](https://ArcGIS.github.io/arcgis-pro-sdk/images/Renderers/graduatedColorOutline.png "Graduated colors with natural breaks renderer.") 
/// </summary>
{
  //Check feature layer name
  //Code works with the USDemographics feature layer available with the ArcGIS Pro SDK Sample data
  var featureLayer = MapView.Active.Map.GetLayersAsFlattenedList().OfType<FeatureLayer>().FirstOrDefault(f => f.Name == "USDemographics");
  if (featureLayer == null)
  {
    MessageBox.Show("This renderer works with the USDemographics feature layer available with the ArcGIS Pro SDK Sample data", "Data missing");
  }
  //Gets the first numeric field of the feature layer
  var firstNumericFieldOfFeatureLayer = "NumericFieldInFeatureLayer";
  //Gets the min and max value of the field
  var minMax = GetFieldMinMax(featureLayer, firstNumericFieldOfFeatureLayer);
  GraduatedColorsRendererDefinition gcDef = new GraduatedColorsRendererDefinition()
  {
    ClassificationField = "NumericFieldInFeatureLayer",
    ClassificationMethod = ClassificationMethod.NaturalBreaks,
    BreakCount = 5,
    ColorRamp = colorRamp
  };
  CIMClassBreaksRenderer renderer = (CIMClassBreaksRenderer)featureLayer.CreateRenderer(gcDef);
  //Create array of CIMVisualVariables to hold the outline information.
  var visualVariables = new CIMVisualVariable[] {
              new CIMSizeVisualVariable
              {
                  ValueExpressionInfo = new CIMExpressionInfo
                  {
                     Title = "Custom",
                     Expression = "$feature.AREA",
                     ReturnType = ExpressionReturnType.Default
                  },
                  AuthoringInfo = new CIMVisualVariableAuthoringInfo
                  {
                      MinSliderValue = Convert.ToDouble(minMax.Item1),
                      MaxSliderValue = Convert.ToDouble(minMax.Item2),
                      ShowLegend = false,
                      Heading = firstNumericFieldOfFeatureLayer
                  },
                  VariableType = SizeVisualVariableType.Graduated,
                  Target = "outline",
                  MinSize = 1,
                  MaxSize = 13,
                  MinValue = Convert.ToDouble(minMax.Item1),
                  MaxValue = Convert.ToDouble(minMax.Item2)
              },

          };
  renderer.VisualVariables = visualVariables;
  //Note: Run within QueuedTask
  featureLayer?.SetRenderer(renderer);
}