委托System.Action< dynamic，int>不接受"1"参数 [英] Delegate System.Action<dynamic,int> does not take `1' arguments

问题描述

我正在尝试从此存储库构建 PostgreSqlGeneration 代码在单声道上.不幸的是，我收到一个我不明白的错误.

I am trying to build the PostgreSqlGeneration code from this repository on Mono. Unfortunately I get an error I do not understand.

在 PostgreSqlMigrationSqlGenerator 中类中，以下方法给出了构建错误委托System.Action不带'1'参数":

In the PostgreSqlMigrationSqlGenerator class the following method gives the build error "delegate System.Action does not take `1' arguments":

private void GenerateStatements(IEnumerable<MigrationOperation> migrationOperations)
{

    Check.NotNull(migrationOperations, "migrationOperations");
    DetectHistoryRebuild(migrationOperations).Each<dynamic>(o => Generate(o)); // <=here!

}

/edit扩展方法的签名如下:

/edit The signature of the extension method is as follows:

/edit 2.这是 Generate 方法的声明:

/edit 2. Here is the declaration for Generate method:

private void Generate(HistoryOperation migration)
{
    //migration

    Check.NotNull(migration, "historyOperation");

    using (var writer = Writer())
    {
        migration.CommandTrees.Each(
            commandTree =>
            {

                switch (commandTree.CommandTreeKind)
                {
                    case DbCommandTreeKind.Insert:


                        writer.Write(GetInsertHistorySql((DbInsertCommandTree)commandTree));

                       break;
                }
            });

        Statement(writer);
    }

}

我不知道为什么会这样，因为 Each 仅具有 dynamic 类型，没有整数.但是我对这种lambda表达式的经验并不丰富.为了了解更多信息并使迁移工作，我希望有人可以解释为什么会发生错误以及如何解决该错误.

I do not know why that happens since the Each only has a dynamic type and no integer one. But I am not that experienced with such lambda expressions. To learn more and to get the migrations to work I hope someone can explain why the error happens and how it can be fixed.

推荐答案

免责声明:我真的很遗憾，找不到任何能解释为何此操作无效的任何内容.如果有人知道请告诉我.Google在这里失败了.

Disclaimer: I feel really bad that I cannot find anything that explains why this isn't working. If someone knows; please tell me. Google has failed here.

很显然，编译器为 Each 选择了错误的重载.库中有两种，一种采用 Action< T> ，另一种采用 Action< T，int> .

Clearly the compiler is picking the wrong overload for Each. There are two in the library, one that takes an Action<T> and another that takes an Action<T, int>.

如果您不使用 dynamic ，它会很好地工作(如果我不得不猜测的话)；但是 dynamic 会引起各种奇怪的问题； plus 您正在使用Mono.

If you weren't using dynamic it would work fine (if I had to guess); but dynamic causes all sorts of weird issues; plus you are using Mono.

由于编译器坚持要求您使用其他重载，因此该解决方案非常简单.只需使用它！

Since the compiler insists you use the other overload, the solution is simple enough. Just use it!

DetectHistoryRebuild(migrationOperations).Each<dynamic>((o, i) => Generate(o));

您使用了一个额外的参数，并且没有使用它.这不是世界末日.

You took an extra parameter and didn't use it. Its not the end of the world.

您还可以显式实例化 Action ，这样编译器就不必选择:

You could also just explicitly instantiate the Action so the compiler doesn't have to choose:

DetectHistoryRebuild(migrationOperations).Each<dynamic>(new Action(o => Generate(o)));

这篇关于委托System.Action< dynamic，int>不接受"1"参数的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！