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();
    }