swiftlang/swift

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

Open

#48,389 创建于 2017年9月1日

在 GitHub 查看
 (8 评论) (0 反应) (0 负责人)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.

贡献者指南

技术栈
swift
领域
developer experience
议题类型
feature
难度面向新贡献者的预计实现难度，1 表示很小改动，5 表示专家级工作。
3
预计时间有经验贡献者完成调查、实现、测试并准备 pull request 的粗略时间范围。
half day
活动状态议题当前的可参与程度：新鲜、活跃、陈旧、阻塞或等待维护者输入。
stale
清晰度议题是否清楚说明期望改动、验收标准和下一步。
clear
前置要求
SwiftCompiler diagnosticsType casting
新手友好度1-100 的估计分数，表示该议题对首次贡献者的友好程度。
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.