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,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,fB,floatPredicate(fA,fB));

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

    Console.ReadLine();
  }