Scala语言特性增加/删除过于频繁了，标准库都重写过好几次。。。，导致大量的版本之间的不兼容性。
这些对业界使用很不友好。

比如一个类型通配符，从scala3.0 到scala3.3就一直在变：

A step-by-step migration is made possible with the following measures:

In Scala 3.0, both _ and ? are legal names for wildcards.
In Scala 3.1, _ is deprecated in favor of ? as a name for a wildcard. A -rewrite option is available to rewrite one to the other.
In Scala 3.2, the meaning of _ changes from wildcard to placeholder for type parameter.
The Scala 3.1 behavior is already available today under the -source future setting.
To smooth the transition for codebases that use kind-projector, we adopt the following measures under the command line option -Ykind-projector:

In Scala 3.0, * is available as a type parameter placeholder.
In Scala 3.2, * is deprecated in favor of _. A -rewrite option is available to rewrite one to the other.
In Scala 3.3, * is removed again, and all type parameter placeholders will be expressed with _.

【 在 fs0 的大作中提到: 】
: 之前写了两年scala，现在三年没写，好多都看不懂了。
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FROM 183.192.18.*