如何在具有空成员的 ValueTuple 中动态迭代/检测成员类型?

问题描述

我正在尝试使用 ValueTuple 在泛型方法的参数列表中简洁地输入 N 类型的列表，然后迭代该类型列表.

I'm trying to make use of ValueTuple to concisely enter a list of N types in a generic method's parameter list, and then later iterate that list of types.

但是，我在迭代类型时遇到了问题，因为初始 Tuple 有 null 成员，所以调用 .GetType() 给了我一个 NullReferenceException.

However, I'm running into a problem when iterating the types, because the initial Tuple has null members, so calling .GetType() gives me a NullReferenceException.

我意识到我可以用实际的 Type 对象列表做我需要的事情，但我更喜欢创建元组时允许的非常简洁的语法……当然，因为这样的事情让我很感兴趣:)

I realize I could do what I need with an actual list of Type objects, but I'd prefer the very concise syntax that's allowed when creating tuples... and of course because things like this intrigue me :)

public static void IterateTupleMemberTypes<T>() where T : ITuple, new()
{
   var tuple = new T();
   for (var i = 0; i < tuple.Length; ++i)
   {
      //First call to GetType() succeeds, first element is an int.
      //Second call to GetType() fails (null ref ex), second element is a string.
      Console.WriteLine($"Item{i} Type: {tuple[i].GetType()}");
   }
}

使用

public class CustomClass
{
   public int ID { get; set; }
}

IterateTupleMemberTypes<(int, string, CustomClass)>();

推荐答案

我认为您正在混合数据和元数据.第一次调用成功，因为 int 是值类型，并且 default(int) 将该值分配给 0，因此它可以工作.这不适用于引用类型，因为它们最初被分配为 null.

I think you are mixing data and metadata.The first call succeed since int is a value type, and default(int) assigns the value to 0, so it works. This won't do for reference types, since these are assigned initially to null.

我相信这里的正确方法是反射 - 并迭代类型的属性，而无需创建实例(因此 new() 限制是多余的).

I believe the proper approach here is, well, reflection - and iterating over the properties of the type, without the need to create an instance (so the new() restriction is redundant).

public static void IterateTupleMemberTypes<T>() where T : ITuple
{
    var tupleGenericArguments = typeof(T).GetGenericArguments();
    for (var i = 0; i < tupleGenericArguments.Length; ++i)
    {
        Console.WriteLine($"Item{i} Type: {tupleGenericArguments[i].Name}");
    }
}

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