swiftlang/swift

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

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#48,389 opened on 2017年9月1日

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bugcompilerdiagnostics qualitygood first issue

説明
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.

コントリビューターガイド

技術スタック
swift
領域
developer experience
Issue 種別
feature
難度新しい貢献者にとっての実装難度です。1 は非常に小さな変更、5 は専門的な作業です。
3
推定時間経験ある貢献者が調査、実装、テスト、pull request 準備にかけるおおよその時間範囲です。
half day
活動状況Issue が今どれだけ取り組みやすいかを示します。新しい、活発、古い、ブロック中、またはメンテナー入力待ちなどです。
stale
明確さ期待される変更、受け入れ条件、次の手順がどれだけ明確かを示します。
clear
前提条件
SwiftCompiler diagnosticsType casting
初心者向け度初回貢献者にどれだけ取り組みやすいかを 1-100 で推定したスコアです。
70
調査方針
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.
[SR-5819] Suggest `as? AnyHashable` when `as? Equatable` or `as? Hashable` is attempted · swiftlang/swift#48389 | Good First Issue