Various API enhancements

src/core/Elsa.Core/Activities/ControlFlow/For.cs

@@ -14,6 +14,17 @@ public enum ForOperator
 
 public class For : Activity
 {
+    public For()
+    {
+    }
+
+    public For(int start, int end, ForOperator forOperator = ForOperator.LessThanOrEqual)
+    {
+        Start = new Input<int>(start);
+        End = new Input<int>(end);
+        Operator = new Input<ForOperator>(forOperator);
+    }
+    
     public Input<int> Start { get; set; } = new(0);
     public Input<int> End { get; set; } = new(0);
     public Input<int> Step { get; set; } = new(1);

src/core/Elsa.Core/Expressions/OutputExpression.cs

@@ -0,0 +1,36 @@
+using Elsa.Contracts;
+using Elsa.Models;
+
+namespace Elsa.Expressions;
+
+public class OutputExpression : IExpression
+{
+    public OutputExpression(Output? output)
+    {
+        Output = output;
+    }
+
+    public OutputExpression()
+    {
+    }
+
+    public Output? Output { get; set; }
+}
+
+public class OutputExpression<T> : OutputExpression
+{
+    public OutputExpression(Output<T>? output) : base(output)
+    {
+    }
+}
+
+public class OutputExpressionHandler : IExpressionHandler
+{
+    public ValueTask<object?> EvaluateAsync(IExpression expression, Type returnType, ExpressionExecutionContext context)
+    {
+        var outputExpression = (OutputExpression)expression;
+        var output = outputExpression.Output;
+        var value = context.Get(output);
+        return ValueTask.FromResult(value);
+    }
+}

src/core/Elsa.Core/Extensions/ActivityExtensions.cs

@@ -33,9 +33,12 @@ public static class ActivityExtensions
 
         return query.Select(x => x!).ToList();
     }
-        
-        
-        
+    
+    /// <summary>
+    /// Creates an input from the activity's result.
+    /// </summary>
+    public static Input<T> CreateInput<T>(this Activity<T> activity) => activity.Result.CreateInput();
+
     public static IEnumerable<Variable> GetVariables(this IActivity activity)
     {
         var properties = activity.GetType().GetProperties();

src/core/Elsa.Core/Extensions/OutputExtensions.cs

@@ -0,0 +1,11 @@
+using Elsa.Models;
+
+namespace Elsa.Extensions;
+
+public static class OutputExtensions
+{
+    /// <summary>
+    /// Creates an input that references the specified output's value.
+    /// </summary>
+    public static Input<T> CreateInput<T>(this Output<T>? output) => new(output);
+}

src/core/Elsa.Core/Models/Activity.cs

@@ -38,4 +38,5 @@ public abstract class ActivityWithResult : Activity
 
 public abstract class Activity<T> : ActivityWithResult
 {
+    public new Output<T>? Result { get; set; }
 }

src/core/Elsa.Core/Models/ExpressionExecutionContext.cs

@@ -26,6 +26,8 @@ public class ExpressionExecutionContext
     public object Get(RegisterLocationReference locationReference) => GetLocation(locationReference).Value!;
     public T Get<T>(RegisterLocationReference locationReference) => (T)Get(locationReference);
     public T? Get<T>(Input<T>? input) => input != null ? (T?)GetLocation(input.LocationReference).Value : default;
+    public T? Get<T>(Output<T>? output) => output != null ? (T?)GetLocation(output.LocationReference).Value : default;
+    public object? Get(Output? output) => output != null ? GetLocation(output.LocationReference).Value : default;
     public T? GetVariable<T>(string name) => (T?)GetVariable(name);
     public T? GetVariable<T>() => (T?)GetVariable(typeof(T).Name);
 

src/core/Elsa.Core/Models/Input.cs

@@ -40,6 +40,14 @@ public class Input<T> : Input
     public Input(Variable<T> variable) : base(new VariableExpression(variable), variable, typeof(T))
     {
     }
+    
+    public Input(Output<T>? output) : base(new OutputExpression<T>(output), output?.LocationReference ?? new Literal(), typeof(T))
+    {
+    }
+    
+    public Input(Output? output) : base(new OutputExpression(output), output?.LocationReference ?? new Literal(), typeof(T))
+    {
+    }
 
     public Input(Literal<T> literal) : base(new LiteralExpression(literal.Value), literal, typeof(T))
     {

src/core/Elsa.Core/Models/NodeIdentity.cs

@@ -1,3 +0,0 @@
-namespace Elsa.Models;
-
-//public record NodeIdentity(ActivityNode ActivityNode, string NodeName);