Undefined symbols for architecture arm64: objc-class-ref in TUICommonTextCell.old: symbol(s) not found for architecture arm64
clang: error: linker command failed with e
在Haskell中,我们有一个有趣的事实,任何同时是Functor和Contravariant的类型构造函数f :: * -> *在其类型参数中都是幻影: phantom :: (Functor f,Contravariant f) => f x -> f y 另一种说法是,对于某些Functor,同时是Contravariant和Const x的每个类型构造函数自然与x同构。这意味着实例化类的“唯一”方法(直到同构): class