问题描述
例如， List [T] forSome {type T} 相当于 List [_] ，但对于 forSome 的所有可能用法都适用，或者有些情况下 forSome 不能被等价的第二个语法？
For instance, List[T] forSome { type T } is equivalent to List[_], but is this true for every possible usage of forSome or are there cases where forSome cannot be replaced by an equivalent of the second syntax?
推荐答案
不，所有的用法都可以这样转换。像这样的东西（感谢 retronym ，下面，谁应该得到这个赞赏）
No, not all usages can be thus converted. Something like this (thanks to retronym, below, who should be getting the upvotes on this one)
def foo(xs: Map[T, T] forSome { type T})
是我可以在不止一个地方使用存在，但是它是相同的存在。显然，如果你使用通配符，你会指的是不同的存在
The point here is that I can use the existential in more than one place but it is the same existential. Obviously, if you used wildcards, you would be referring to different existentials
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