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(, 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 >=
             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(, 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。