c# - 静态 ImmutableArray 未初始化

Question

我有一个带有静态成员的内部静态类 MyLists:

internal static ImmutableArray<string> MyList = 
    new ImmutableArray<string> { "asd", "qwe" };

在另一个公共(public)测试类 Tests 中，我有一个 MyTest 函数来选择和比较列表。

[TestClass]
public class MyTests {
  [TestMethod]
  public void TestMyLists() {
    var list = MyLists.MyList.Select(s => s + ".foo");
  }
}

但是，我收到以下错误:

Additional information: The type initializer for 'TestMyLists' threw an exception.
Object reference not set to an instance of an object.

当我调试时，我看到静态 ImmutableArray 的值 = 未初始化。为什么？

Answer 1

根据 ImmutableArray 上的文档, 你应该使用 Create()方法而不是对这种类型的数组使用构造函数，如下所示:

internal static ImmutableArray<string> List = ImmutableArray.Create("asd", "qwe");

关于为什么，我会点你这篇文章Please welcome ImmutableArray由 Immo Landwerth 撰写，他在其中描述:

The default value of ImmutableArray<T> has the underlying array initialized with a null reference. In this case it behaves the same way as an ImmutableArray<T> that has been initialized with an empty array, i.e. the Length property returns 0 and iterating over it simply doesn’t yield any values. In most cases this is the behavior you would expect. However, in some cases you may want to know that the underlying array hasn’t been initialized yet. For that reason ImmutableArray<T> provides the property IsDefault which returns true if the underlying array is a null reference. For example you can use that information to implement lazy initialization.