问题描述
这会导致编译时异常:
public sealed class ValidatesAttribute<T> : Attribute
{
}
[Validates<string>]
public static class StringValidation
{
}
我意识到 C# 不支持通用属性.然而，经过多次谷歌搜索，我似乎无法找到原因.
I realize C# does not support generic attributes. However, after much Googling, I can't seem to find the reason.
有谁知道为什么泛型类型不能从 Attribute 派生?有什么理论吗?
Does anyone know why generic types cannot derive from Attribute? Any theories?
推荐答案
好吧，我无法回答为什么它不可用，但我可以确认这不是 CLI 问题.CLI 规范没有提到它(据我所知)，如果您直接使用 IL，您可以创建一个通用属性.C# 3 规范中禁止它的部分 - 第 10.1.4 节类基础规范"没有给出任何理由.
Well, I can't answer why it's not available, but I can confirm that it's not a CLI issue. The CLI spec doesn't mention it (as far as I can see) and if you use IL directly you can create a generic attribute. The part of the C# 3 spec that bans it - section 10.1.4 "Class base specification" doesn't give any justification.
带注释的 ECMA C# 2 规范也没有提供任何有用的信息，尽管它确实提供了一个不允许的示例.
The annotated ECMA C# 2 spec doesn't give any helpful information either, although it does provide an example of what's not allowed.
我的带注释的 C# 3 规范副本将于明天到达...我会看看是否能提供更多信息.无论如何，这绝对是语言决定而不是运行时决定.
My copy of the annotated C# 3 spec should arrive tomorrow... I'll see if that gives any more information. Anyway, it's definitely a language decision rather than a runtime one.
Eric Lippert 的回答(释义):没有特别的原因，除了避免语言和编译器的复杂性，用于不会增加太多价值的用例.
Answer from Eric Lippert (paraphrased): no particular reason, except to avoid complexity in both the language and compiler for a use case which doesn't add much value.
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