无法在 ArrayList 和 Array 之间应用 ??-operator [英] Cannot apply ??-operator between an ArrayList and an Array

问题描述

我有这样的代码:

foreach (Type t in types ?? asm.GetTypes())

哪个应该循环 ArrayList types 或程序集类型中的所有类型，如果没有提供类型.由于 System.Array 和 System.Collections.ArrayList 都实现了 IEnumerable，我希望该循环能够正常工作.

Which should loop all types in the ArrayList types or the assemblies types if no types are provided. As both System.Array as System.Collections.ArrayList implement IEnumerable I´d expect that loop to work.

然而编译器抱怨:

运算符??"不能应用于类型为System.Collections.ArrayList"和System.Type[]"的操作数

Operator '??' cannot be applied to operands of type 'System.Collections.ArrayList' and 'System.Type[]'

我想我遗漏了一些非常明显的东西，但它是什么?

I suppose I am missing something very obvious, but what is it?

推荐答案

你真的不应该在 2015 年使用 ArrayList.ArrayList 不支持 IEnumerable<> 接口.

You shouldn't really use ArrayList in 2015. ArrayList doesn't support the IEnumerable<> interface.

您可以强制使用 IEnumerable 非通用接口:

You can force the using of the IEnumerable non-generic interface:

foreach (Type t in (IEnumerable)types ?? asm.GetTypes())

您的错误发生是因为 ?? 运算符没有搜索左右之间的最小公共类型.它只是检查是否可以将右类型隐式转换为左类型，或者是否可以将左类型隐式转换为右类型.显然Type[]不能转换为ArrayList，ArrayList不能转换为Type[].

Your error happens because the ?? operator doesn't search for the minimum common type between left and right. It simply checks if right type can be implicitly converted to left type or if left type can be implicitly converted to right type. Clearly Type[] can't be converted to ArrayList and ArrayList can't be converted to Type[].

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