c# - 有没有办法将 lambda 表达式作为变量或参数传递？

Question

我需要将 lambda 查询作为参数传递，下面的代码是示例，我很想为它找到一个实现，有示例:像这样的东西:

var expr1 = Where(n => n > 6).OrderBy(n => n % 2 == 0).Select(n => n);
var expr2 = TakeWhile((n, index) => n >= index));

然后像这样使用它:

public void UseLambda<T> (IEnumerable<T> source , lambda Expr){

var items= Expr.Compile(source);

foreach(var item in items)
     Console.Writeline(item.ToString());
}

public void Main(){
    List<int> numbers = new List<int> { 10, 24, 9, 87, 193, 12, 7, 2, -45, -2, 9 };
    var expr1 = Where(n => n > 6).OrderBy(n => n % 2 == 0).Select(n => n);
    UseLambda(numbers, expr1);
}

有人知道吗？

Answer 1

检查 Func(Of T, TResult) Delegate (MSDN)

using System;

public class LambdaExpression
{
   public static void Main()
   {
       Func<string, string> convert = s => s.ToUpper();

       string name = "Dakota";
       Console.WriteLine(convert(name));   
   }
}

来自MSDN

The underlying type of a lambda expression is one of the generic Func delegates. This makes it possible to pass a lambda expression as a parameter without explicitly assigning it to a delegate. In particular, because many methods of types in the System.Linq namespace have Func(Of T, TResult) parameters, you can pass these methods a lambda expression without explicitly instantiating a Func(Of T, TResult) delegate.

编辑

您的案例的可能解决方案

static void Main(string[] args) 
{
    List<int> numbers = new List<int> { 10, 24, 9, 87, 193, 12, 7, 2, -45, -2, 9 };
    Func<IEnumerable<int>, IEnumerable<int>> expr = n => n.Where(n1 => n1 > 6).OrderBy(n1 => n1 % 2 == 0).Select(n1 => n1);
    UseLambda<int>(numbers, expr);
}
private static void UseLambda<T>(List<T> numbers, 
                                 Func<IEnumerable<T>, 
                                 IEnumerable<T>> expr) 
{
    var values = expr(numbers);
    foreach (var item in values) {
       Console.WriteLine(item);
    }
}