在线编译器中的静态字段变量初始值设定项失败但在 VS 中有效

Question

我想澄清一下 .NET 中静态字段初始值设定项的执行时间有多宽松。在在线编译器 (Fiddle) 中运行下面的代码时，我得到了 TypeInitializationException，但我在测试控制台应用程序中得到了预期的输出 1在 VS.

代码：

using System;
using SimpleInjector;   

public class Program
{
    public static IFactory Factory { get; set; }
        
    public interface IFactory { T GetInstance<T>() where T: class; }
    
    public class SimpleFactory: IFactory
    {
        private readonly Container _container;
        public SimpleFactory(Container container) { this._container = container; }
        public T GetInstance<T>() where T : class { return _container.GetInstance<T>(); }
    }
    
    public class Bar { public int Get() { return 1; } }

    public static class Foo
    {
        //static Foo() {}
        public static readonly int foo = Factory.GetInstance<Bar>().Get();
    }
        
    public static void Main()
    {
        var container = new Container();
        var factory = new SimpleFactory(container);
        
        container.RegisterInstance(Factory = factory);
        container.Register<Bar>();
                
        Console.WriteLine(Foo.foo);
    }
}

来自在线编译的堆栈跟踪：

[System.NullReferenceException: Object reference not set to an instance of an object.]
   at Program.Foo..cctor() :line 22

[System.TypeInitializationException: The type initializer for 'Foo' threw an exception.]
   at Program.Main() :line 33

什么给了？可以安全地假设在 visual studio 下构建时代码始终保证正常工作吗？谢谢你的时间。

Answer 1

根据C# language spec，这被特别指出为依赖于实现的东西：

If a static constructor exists in the class, execution of the static field initializers occurs immediately prior to executing that static constructor. Otherwise, the static field initializers are executed at an implementation-dependent time prior to the first use of a static field of that class.

您获得的唯一保证是，在首次使用静态字段之前必须一段时间。

但是，正如您可能已经在 fiddle 中发现的那样，添加静态构造函数可以实现此目的。静态构造函数保证静态字段初始化器紧接在静态构造函数之前运行。好消息是静态构造函数的执行不依赖于实现(spec):

The execution of a static constructor is triggered by the first of the following events to occur within an application domain:

An instance of the class type is created.

Any of the static members of the class type are referenced.

在线编译器中的静态字段变量初始值设定项失败但在 VS 中有效

static field variable initializer FAILS in online compiler but works in VS

.net

c#

static

field

typeinitializer