c# - "variable ' ' of type ' ' referenced from scope ' ', but it is not defined"

Question

我的代码收到此错误消息:“从范围‘’引用了‘System.Int32’类型的变量‘assignVal’，但未定义”

我检查过

• Lambda compilation throws "variable '' of type '' referenced from scope '', but it is not defined"
• variable '' of type '' referenced from scope '', but it is not defined

但不幸的是，我的示例似乎更简单，但由于某种原因仍然无法正常工作。

这是我的代码:

using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Linq.Expressions;
using System.Reflection.Emit;
using System.Threading.Tasks;
using static System.Linq.Expressions.Expression;

namespace ExpressionTests
{
    class Program
    {
        static async Task Main(string[] args)
        {
            Console.WriteLine(GetSyncAddExpression()(5) == 6);
            Console.ReadKey();

            Console.WriteLine(await GetTaskAddExpression()(5) == 6);
            Console.ReadKey();
        }

        private static Func<int, Task<int>> GetTaskAddExpression()
        {
            var fromResultMethod = typeof(Task).GetMethod(nameof(Task.FromResult)).MakeGenericMethod(typeof(int));

            var inParam = Parameter(typeof(int), "p1");
            var assignmentValue = Variable(typeof(int), "assignVal");
            var retVal = Variable(typeof(Task<int>));

            var lambda = Lambda<Func<int, Task<int>>>(Block(
                Assign(assignmentValue, Add(inParam, Constant(1))),
                Assign(retVal, Call(null, fromResultMethod, assignmentValue)),
                retVal
            ), inParam);

            if (Debugger.IsAttached)
                Debugger.Break();

            return lambda.Compile();
        }

        private static Func<int, int> GetSyncAddExpression()
        {
            var inParam = Parameter(typeof(int), "p1");
            var assignmentValue = Variable(typeof(int), "assignVal");
            var retVal = Variable(typeof(int));

            var lambda = Lambda<Func<int, int>>(Block(
                Assign(assignmentValue, Add(inParam, Constant(1))),
                Assign(retVal, assignmentValue),
                retVal
            ), inParam);

            if (Debugger.IsAttached)
                Debugger.Break();

            return lambda.Compile();
        }
    }
}

这个代码示例看起来很简单，它应该按原样工作，我正在重用这些表达式，所以我不太明白为什么我会收到这个错误。

Answer 1

您没有在 Block 调用中包含要使用的变量。

如果你改变这个:

var lambda = Lambda<Func<int, int>>(Block(
    Assign(assignmentValue, Add(inParam, Constant(1))),
    Assign(retVal, assignmentValue),
    retVal
), inParam);

对此:

var lambda = Lambda<Func<int, int>>(Block(
    // This is the line I've added
    new[] { assignmentValue, retVal },
    Assign(assignmentValue, Add(inParam, Constant(1))),
    Assign(retVal, assignmentValue),
    retVal
), inParam);

它工作正常。

基本上您使用的是 Block(params Expression[]) 重载，它仅适用于没有变量的 block 。