为什么有人声称Java的泛型实现不好？ [英] Why do some claim that Java's implementation of generics is bad?

问题描述

偶尔有人听说，用泛型来说，Java并没有得到正确的答案。 （最近的参考，这里）

请原谅我的经验不足，但是会让他们变得更好吗？

• 类型信息在编译时会丢失，所以在执行时你不能说出它的意思是什么类型的元素


• 不能用于值类型（这是一个biggie - 在.NET中， List< byte> 确实由

• 调用泛型方法的语法太糟糕了（IMO）


约束语法可能令人困惑

• 通配符通常很混乱


• 由于上述操作等原因而导致各种限制





好：

• 通配符允许在调用端指定协变/这在很多情况下非常整洁


• 总比没有好！

I've occasionally heard that with generics, Java didn't get it right. (nearest reference, here)

Pardon my inexperience, but what would have made them better?

解决方案

Bad:

• Type information is lost at compile time, so at execution time you can't tell what type it's "meant" to be
• Can't be used for value types (this is a biggie - in .NET a List<byte> really is backed by a byte[] for example, and no boxing is required)
• Syntax for calling generic methods sucks (IMO)
• Syntax for constraints can get confusing
• Wildcarding is generally confusing
• Various restrictions due to the above - casting etc

Good:

• Wildcarding allows covariance/contravariance to be specified at calling side, which is very neat in many situations
• It's better than nothing!

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