Mono.Csharp脚本中Lambdas内部的变量不起作用

本文关键字：变量 不起作用 内部 Lambdas Csharp 脚本 Mono | 更新日期: 2023-09-27 18:20:59

thows Mono.Sharp.InternalError异常。InnerException基本上说没有设置对象引用。大家有什么想法吗？使用的代码：

using System;
using System.IO;
using Mono.CSharp;
using System.Reflection;
using System.Collections.Generic;
namespace TestMonoCSharp
{
    public class testmodel
    {
        public string a {get;set;}
        public double b {get;set;}
    }
    class MainClass
    {
        public static void Main (string[] args)
        {
            var tw = new StreamWriter(new MemoryStream());
            tw.AutoFlush = true;
            CompilerContext c = new CompilerContext(new CompilerSettings(), new StreamReportPrinter(tw));
            var csc = new Evaluator(c);
            csc.ReferenceAssembly(Assembly.GetExecutingAssembly());
            csc.Run("using System;");
            csc.Run("using System.Linq;");
            csc.Run("using System.Collections.Generic;");
            csc.Run("using TestMonoCSharp;");
            var query = @"new System.Func<IEnumerable<testmodel>, IEnumerable<testmodel>>((pos) => 
                        {
                            var avg = pos.Average(x=>x.b);
                            //return pos.Where(x=>x.b < 3 ).ToArray(); //works
                            return pos.Where(x=>x.b < avg ).ToArray(); //doesn't work
                        });";
            var list = new List<testmodel> () {new testmodel{ a = "a", b = 3}, new testmodel{ a = "a", b = 2} };
            var func = csc.Evaluate(query) as Func<IEnumerable<testmodel>, IEnumerable<testmodel>>;            
            var val  = func(list);
        }
    }
}

Mono.Csharp脚本中Lambdas内部的变量不起作用

您正在尝试评估Delegate。。。

new System.Func<IEnumerable<string>, IEnumerable<string>>((pos) =>                         {
   var avg = pos.Average(x=>x.Length);
   return pos.Where(x=>x.Length < avg ).ToArray(); //doesn't work
});

这会导致mcs编译器中出现内部System.NullReferenceException，因为该语句的执行无法动态评估任何内容，因为它没有上下文

剪切/粘贴到Mono的csharp-repl:

public class testmodel
    {
        public string a {get;set;}
        public double b {get;set;}
    }
testmodel[] list = {new testmodel{a="1",b=1}, new testmodel{a="22",b=2}, new testmodel{a="333",b=3}, new testmodel{a="4444",b=4}, new testmodel{a="55555", b=5}}
var averageEvaluator = new System.Func<IEnumerable<testmodel>, IEnumerable<testmodel>>((pos) =>                         {
   var avg = pos.Average(x=>x.b);
   return pos.Where(x=>x.b < avg ).ToArray();
})
var results = averageEvaluator(list)
foreach(var x in results){ print(x.a);}
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