这是文档的锅,主要是这里有一个递归的声明 SubSequence.SubSequence == SubSequence
,所以文档生成器才被绕进去了,实际声明的代码其实很简单:
// https://github.com/apple/swift/blob/master/stdlib/public/core/Collection.swift
protocol Collection: Sequence {
override associatedtype Element
associatedtype Index: Comparable
associatedtype SubSequence: Collection where SubSequence.Index == Index,
Element == SubSequence.Element,
SubSequence.SubSequence == SubSequence
...
}