Compare updated template evaluator (#4092)

src/Sdk/Expressions/Sdk/Functions/Join.cs

@@ -0,0 +1,76 @@
+#nullable disable // Consider removing in the future to minimize likelihood of NullReferenceException; refer https://learn.microsoft.com/en-us/dotnet/csharp/nullable-references
+
+using System;
+using System.Text;
+
+namespace GitHub.Actions.Expressions.Sdk.Functions
+{
+    internal sealed class Join : Function
+    {
+        protected sealed override Boolean TraceFullyExpanded => true;
+
+        protected sealed override Object EvaluateCore(
+            EvaluationContext context,
+            out ResultMemory resultMemory)
+        {
+            resultMemory = null;
+            var items = Parameters[0].Evaluate(context);
+
+            // Array
+            if (items.TryGetCollectionInterface(out var collection) &&
+                collection is IReadOnlyArray array &&
+                array.Count > 0)
+            {
+                var result = new StringBuilder();
+                var memory = new MemoryCounter(this, context.Options.MaxMemory);
+
+                // Append the first item
+                var item = array[0];
+                var itemResult = EvaluationResult.CreateIntermediateResult(context, item);
+                var itemString = itemResult.ConvertToString();
+                memory.Add(itemString);
+                result.Append(itemString);
+
+                // More items?
+                if (array.Count > 1)
+                {
+                    var separator = ",";
+                    if (Parameters.Count > 1)
+                    {
+                        var separatorResult = Parameters[1].Evaluate(context);
+                        if (separatorResult.IsPrimitive)
+                        {
+                            separator = separatorResult.ConvertToString();
+                        }
+                    }
+
+                    for (var i = 1; i < array.Count; i++)
+                    {
+                        // Append the separator
+                        memory.Add(separator);
+                        result.Append(separator);
+
+                        // Append the next item
+                        var nextItem = array[i];
+                        var nextItemResult = EvaluationResult.CreateIntermediateResult(context, nextItem);
+                        var nextItemString = nextItemResult.ConvertToString();
+                        memory.Add(nextItemString);
+                        result.Append(nextItemString);
+                    }
+                }
+
+                return result.ToString();
+            }
+            // Primitive
+            else if (items.IsPrimitive)
+            {
+                return items.ConvertToString();
+            }
+            // Otherwise return empty string
+            else
+            {
+                return String.Empty;
+            }
+        }
+    }
+}