学习ExpressionTree(做装配脑袋出的练习题)

 1             // 第一题：画出下列表达式的表达式树。一开始，您很可能不知道某些操作其实也是表达式（比如取数组的运算符a[2]），不过没有关系，后面的习题将帮你验证这一点。

            //-a
            ParameterExpression e1 = Expression.Variable(typeof(int), "a");
            UnaryExpression u = Expression.Negate(e1);//求反的表达式
            Console.WriteLine(u);

            //a + b * 2
            ParameterExpression a = Expression.Variable(typeof(double), "a");
            ParameterExpression b = Expression.Variable(typeof(double), "b");
            ConstantExpression t = Expression.Constant(2d,typeof(double));
            BinaryExpression cf = Expression.Multiply(b, t);
            BinaryExpression jf = Expression.Add(a, cf);
            Console.WriteLine(jf);

           // Math.Sin(x) + Math.Cos(y)
            ParameterExpression px = Expression.Parameter(typeof(double), "x");
            MethodCallExpression sin = Expression.Call(null, typeof(Math).GetMethod("Sin", BindingFlags.Static | BindingFlags.Public), px);

            ParameterExpression py = Expression.Parameter(typeof(double), "y");
            MethodCallExpression cos = Expression.Call(null,
                typeof(Math).GetMethod("Cos", BindingFlags.Public | BindingFlags.Static), py);

            BinaryExpression jf = Expression.Add(sin, cos);

            Console.WriteLine(jf.ToString());

           // new StringBuilder(“Hello”)
            ConstantExpression s = Expression.Constant("Hello", typeof(string));
            NewExpression n = Expression.New(typeof(StringBuilder).GetConstructor(new Type[] { typeof(string) }), s);
            Console.WriteLine(n.ToString());

           // new int[] { a, b, a + b}
            ParameterExpression a = Expression.Variable(typeof(int), "a");
            ParameterExpression b = Expression.Variable(typeof(int), "b");
            BinaryExpression c = Expression.Add(a, b);
            NewArrayExpression n = Expression.NewArrayInit(typeof(int),a,b,c);
            Console.WriteLine(n);
            //a[i – 1] * i
            ParameterExpression pi = Expression.Variable(typeof(int), "i");
            ConstantExpression o = Expression.Constant(1, typeof(int));
            BinaryExpression j = Expression.Subtract(pi, o);
            ParameterExpression arr = Expression.Variable(typeof(int[]),"a");
            IndexExpression t = Expression.ArrayAccess(arr, j);

            BinaryExpression cf = Expression.Multiply(t, pi);
            Console.WriteLine(cf);

            a.Length > b | b >= 0
            ParameterExpression a = Expression.Variable(typeof(string), "a");
            MemberExpression m = Expression.Property(a, typeof(string).GetProperty("Length"));
            ParameterExpression b = Expression.Variable(typeof(int), "b");
            BinaryExpression g = Expression.GreaterThan(m, b);

            ConstantExpression z = Expression.Constant(0, typeof(int));
            BinaryExpression b2 = Expression.GreaterThanOrEqual(b, z);

            BinaryExpression b3 = Expression.Or(g, b2);
            Console.WriteLine(b3);

            //（高难度）new System.Windows.Point() { X = Math.Sin(a), Y = Math.Cos(a) }
            NewExpression n = Expression.New(typeof(System.Windows.Point));//new System.Windows.Point() 
            ParameterExpression a = Expression.Variable(typeof(double), "a");
            MethodCallExpression sin = Expression.Call(null, typeof(Math).GetMethod("Sin"), a);
            UnaryExpression sinD = Expression.Convert(sin, typeof(double));
            MethodCallExpression cos = Expression.Call(null, typeof(Math).GetMethod("Cos"), a);
            UnaryExpression cosD = Expression.Convert(cos, typeof(double));
            MemberAssignment as1 = Expression.Bind(typeof(System.Windows.Point).GetProperty("X"), sinD);
            MemberAssignment as2 = Expression.Bind(typeof(System.Windows.Point).GetProperty("Y"), cosD);

            MemberInitExpression mm = Expression.MemberInit(n, as1, as2);

            LambdaExpression le = Expression.Lambda(mm, a);
            
            Console.WriteLine(le.Body);

            //提示：注意运算符的优先级。倒数第二题的a是String类型，其余变量你可以用任意合适的简单类型。如果想知道以上表达式分别是什么表达式，可以查MSDN。