using System.Linq;
using System.Linq.Expressions;
public static class LambdaExpressionExtensions
{
public static Expression<TFunc> And<TFunc>(this Expression<TFunc> expr1, Expression<TFunc> expr2)
{
if (expr1.ReturnType != typeof(bool) || expr2.ReturnType != typeof(bool))
throw new ArgumentException("both lambda expressions must return boolean type");
if (expr1.Parameters.Zip(expr2.Parameters, (p1, p2) => p1.Type == p2.Type).Any(x => x == false))
throw new ArgumentException("expr1 and expr2 must have exactly the same parameters"); var p = expr1.Parameters;
var left = Expression.Invoke(expr1, p);
var right = Expression.Invoke(expr2, p);
var expr = Expression.And(left, right);
return Expression.Lambda<TFunc>(expr, p);
}
}
这里在3.5有三个地方出错
1:expr1.ReturnType
2:expr1.Parameters.Zip
3:Expression.Invoke(expr1, p)前两个没有办法解决没什么,我可以注释掉
但第三个方法是必须的谢谢
那个是3.5不支持协变造成的,对于System.Collections.Generic.IEnumerable<Expression>接口,需要协变到ReadOnlyCollection<ParameterExpression>,该功能只有4.0以上才提供,不过转换为数组的话,就可以用第二种重载,不需要协变了。
http://bbs.csdn.net/topics/390303038
谢谢
{
if (expr1.Body.Type != typeof(bool) || expr2.Body.Type != typeof(bool))
throw new ArgumentException("both lambda expressions must return boolean type");
if (expr1.Parameters.Zip(expr2.Parameters, (p1, p2) => p1.Type == p2.Type).Any(x => x == false))
throw new ArgumentException("expr1 and expr2 must have exactly the same parameters"); var p = expr1.Parameters;
var left = Expression.Invoke(expr1, p.ToArray());
var right = Expression.Invoke(expr2, p.ToArray());
var expr = Expression.And(left, right);
return Expression.Lambda<TFunc>(expr, p);
} public static IEnumerable<TResult> Zip<TFirst, TSecond, TResult>(this IEnumerable<TFirst> first, IEnumerable<TSecond> second, Func<TFirst, TSecond, TResult> selector)
{
var list1 = first.ToList();
var list2 = second.ToList();
for (int i = 0; i < (list1.Count > list2.Count ? list2.Count : list1.Count); i++)
{
yield return selector(list1[i], list2[i]);
}
}