swift - @_downgrade_exhaustivity_check Swift 私有(private)关键字是什么？

Question

在浏览 Swift 存储库时，我遇到了那个关键字。

这是什么意思？

例如，来自 Time.swift :

public enum DispatchTimeInterval : Equatable {
    case seconds(Int)
    case milliseconds(Int)
    case microseconds(Int)
    case nanoseconds(Int)
    @_downgrade_exhaustivity_check
    case never
}

Answer 1

实际的提交消息状态

Implement @_downgrade_exhaustivity_check

Dispatch requests the ability to add a new case, but to treat missing instances of that case in patterns as warnings instead of errors. It is still an error to make reference to the annotated case in at least one pattern then not cover the rest of the space, but it is not an error to omit the space of patterns referencing the case entirely.

This attribute is private and uglified to intentionally discourage its use outside just this one use case.

来源https://git.snooey.net/Mirrors/swift/commit/03527d9eec65324434011d23219e2bf7525642c6