swiftlang/swift

[SR-5819] Suggest `as? AnyHashable` when `as? Equatable` or `as? Hashable` is attempted

Open

#48,389 建立於 2017年9月1日

在 GitHub 查看
 (8 留言) (0 反應) (0 負責人)Swift (69,989 star) (10,719 fork)batch import
bugcompilerdiagnostics qualitygood first issue

描述
Previous ID SR-5819
Radar None
Original Reporter @jckarter
Type Bug
Votes 0
Component/s Compiler
Labels Bug, DiagnosticsQoI, StarterBug
Assignee None
Priority Medium

md5: 5e4ffb6d40f711123adf86651f9a3a8f

Issue Description:

If you have two values of type Any or otherwise opaque type and you want to test whether they're equal, it's natural to try to write something like:

if let a = a as? Equatable, b = b as? Equatable {
  return a == b
}

Maybe someday that will work, but in the meantime dynamically casting to AnyHashable can get the desired effect. It'd be nice QoI to have a diagnostic telling people they can do this when they try similar things that don't.

貢獻者指南

技術棧
swift
領域
developer experience
議題類型
feature
難度面向新貢獻者的預計實作難度，1 表示很小改動，5 表示專家級工作。
3
預計時間有經驗貢獻者完成調查、實作、測試並準備 pull request 的粗略時間範圍。
half day
活動狀態議題目前的可參與程度：新鮮、活躍、陳舊、阻塞或等待維護者輸入。
stale
清晰度議題是否清楚說明預期改動、驗收標準和下一步。
clear
前置要求
SwiftCompiler diagnosticsType casting
新手友善度1-100 的估計分數，表示該議題對首次貢獻者的友善程度。
70
研究方向
The issue requests a new diagnostic in the Swift compiler when a user attempts to cast to `Equatable` or `Hashable` on a value of opaque type. The fix should suggest `as? AnyHashable` as an alternative. To implement, examine the type checker's logic for handling dynamic casts, likely in `lib/Sema/CastCheck.cpp` or similar. Review the existing diagnostic patterns for fix its. Since this is a QoI improvement, also consider the `DiagnosticsEngine` and how to emit suggestions. The issue has comments that may discuss prior attempts or design considerations.