http://www.dartlang.org/docs/spec/dartLangSpec.pdf
Dart 的语言规范在下面提到
Dart supports optional typing based on interface types. The type system is unsound, due to the covariance of generic types. This is a deliberate choice (and undoubtedly controversial). Experience has shown that sound type rules for generics fly in the face of programmer intuition. It is ..
最佳答案
从吉拉德布拉查 [1]:
You can write a tool that will scream bloody murder about these things, but what you can’t do is stop people from running their programs.
或者，换句话说[2]:
The problem is that expressing type flow fully and explicitly is more difficult for most programmers than writing code that passes values around and deals with runtime type errors when and if they happen. The word chosen for this difference in difficulty is that the latter is more "intuitive" than the former - I don't think it's a particularly bad choice of word. The phenomenon is one of the biggest reasons dynamic languages have become a lot more popular over recent years, a rejection of complexity in specifying static types.
It's like there's another triangle tradeoff: expressive, sound, simple: choose any two for your type system. Almost everyone is unwilling to forgo expressiveness - the object graphs weaved in modern software can be quite tangled indeed - while any language that hopes to have large-scale success cannot start out being anything but fairly simple. So they give up some measure of (statically-typed) soundness, and expect lots of runtime type errors during debugging and testing.
[1] http://blog.sethladd.com/2011/11/transcription-of-quick-tour-of-dart-by.html
[2] http://lambda-the-ultimate.org/node/4377#comment-67589
关于generics - 为什么选择在 Dart 中输入？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/8169141/