pattern

Behavioral/Visitor/csharp/Program.cs

@@ -0,0 +1,70 @@
+using System.Text;
+
+namespace DesignPatters
+{
+    using DictType = Dictionary<Type, Action<Expression, StringBuilder>>;
+
+    public abstract class Expression
+    {
+
+    }
+
+    public class DoubleExpression : Expression
+    {
+        public double Value { get; set; }  
+
+        public DoubleExpression(double value)
+        {
+            this.Value = value;
+        }
+    }
+
+    public class AdditionExpression : Expression
+    {
+        public Expression Left;
+        public Expression Right;
+
+        public  AdditionExpression(Expression left, Expression right)
+        {
+            Left = left ?? throw new ArgumentNullException(paramName: nameof(left));
+            Right = right ?? throw new ArgumentNullException(paramName: nameof(right));
+        }
+    }
+
+    public static class ExpressionPrinter
+    {
+        private static DictType actions = new DictType
+        {
+            [typeof(AdditionExpression)] = (e, sb) =>
+            {
+                var ae = (AdditionExpression)e;
+                sb.Append("(");
+                Print(ae.Left, sb);
+                sb.Append("+");
+                Print(ae.Right, sb);
+                sb.Append(')');
+            },
+            [typeof(DoubleExpression)] = (e, sb) =>
+            {
+                var de = (DoubleExpression)e;
+                sb.Append(de.Value);
+            }
+        };
+        public static void Print(Expression e, StringBuilder sb)
+        {
+            actions[e.GetType()](e, sb);
+        }
+    }
+
+    public class Demo
+    {
+        public static void Main()
+        {
+            var e = new AdditionExpression(new DoubleExpression(2), new AdditionExpression(new DoubleExpression(2),new DoubleExpression(2)));
+            var sb = new StringBuilder();
+            ExpressionPrinter.Print(e, sb);
+            Console.WriteLine(sb.ToString());
+
+        }
+    }
+}