expression表达式树 浅谈c#表达式树Expression简单类型比较demo

using System;
using System.Linq.Expressions;

class DynamicPredicate
{
  public static Expression<Func<T, T, bool>> Generate<T>(string op)
  {
    ParameterExpression x = Expression.Parameter(typeof(T), "x");
    ParameterExpression y = Expression.Parameter(typeof(T), "y");
    return Expression.Lambda<Func<T, T, bool>>
    (
      (op.Equals(">")) ? Expression.GreaterThan(x, y) :
        (op.Equals("<")) ? Expression.LessThan(x, y) :
          (op.Equals(">=")) ? Expression.GreaterThanOrEqual(x, y) :
            (op.Equals("<=")) ? Expression.LessThanOrEqual(x, y) :
              (op.Equals("!=")) ? Expression.NotEqual(x, y) :
                Expression.Equal(x, y),
      x,
      y
    );
  }
}

static void Main()
  {
    string op = ">=";
    var integerPredicate = DynamicPredicate.Generate<int>(op).Compile();
    var floatPredicate = DynamicPredicate.Generate<float>(op).Compile();

    int iA = 12, iB = 4;
    Console.WriteLine("{0} {1} {2} : {3}",
              iA, op, iB, integerPredicate(iA, iB));

    float fA = 867.0f, fB = 867.0f;
    Console.WriteLine("{0} {1} {2} : {3}",
              fA, op, fB, floatPredicate(fA, fB));

    Console.WriteLine("{0} {1} {2} : {3}",
              fA, ">", fB, DynamicPredicate.Generate<float>(">").Compile()(fA, fB));

    Console.ReadLine();
  }