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Swiftの “private” を テストする id:yutailang0119 / @yutailang0119 Mobile Act OSAKA 15 1

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Who am I!? ● id:yutailang0119 ○ @yutailang0119 ● 株式会社はてな ○ @京都オフィス ○ アプリケーションエンジニア ■ iOS/Android ○ サービスプラットフォームチーム ● try! Swift Tokyo Organizer ● AVP座談会 🥽 2

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3 Introduction

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Introduction ● private/fileprivateは、参照範囲を制限 ○ @testableもアクセスできない ○ open, package, internalはアクセス可能 ● Javaには @VisibleForTesting がある ○ https://developer.android.com/reference/androidx/annotation/VisibleForTesting 4

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Access Level 5 ● open ● package ● internal ● fileprivate ● private https://docs.swift.org/swift-book/documentation/the-swift-programming-language/accesscontrol/

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6 Motivation

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Motivation ● テストのためのinternalを避けたい ○ e.g.) 🙅 コメントでの規制 VisibleForTesting ● アクセスのバイパス手段がほしい 7

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8 Proposed solution

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9 yutailang0119/swift-bypass-accessing

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yutailang0119/swift-bypass-accessing ● Swift Macros ○ @BypassAccess ● ___ prefix付きコード生成 PeerMacro ● #if DEBUG & internal 10

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PeerMacro @attached(peer, names: prefixed(___), named(___init)) public macro BypassAccess() = #externalMacro( module: "BypassAccessingMacros", type: "BypassAccessMacro" ) 11

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12 Detailed design

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Detailed design import BypassAccessing struct Declaration { @BypassAccess private let property: String = "property" @BypassAccess fileprivate func function() -> String { #function } } 13

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Detailed design import Testing import BypassAccessing @testable import Example struct Tests { @Test func test() { let declaration = Declaration() #if DEBUG #expect(declaration.___property == "property") #expect(declaration.___function() == "function()") #endif } } 14

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15 Macro

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Macro import BypassAccessing struct Declaration { @BypassAccess private let property: String = "property" } 16

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Expand Macro import BypassAccessing struct Declaration { @BypassAccess private let property: String = "property" #if DEBUG var ___property: String { property } #endif } 17

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Macro import BypassAccessing struct Declaration { @BypassAccess fileprivate func function() -> String { #function } } 18

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Expand Macro import BypassAccessing struct Declaration { @BypassAccess fileprivate func function() -> String { #function } #if DEBUG func ___function() -> String { function() } #endif } 19

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20 Support Grammar

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Support Grammar ● let ● var ○ Stored ○ Computed ● func ● init 21

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Modifier, Accessor ● async, @MainActor ● throws ● static, class ● inout ● Generics 22 https://docs.swift.org/swift-book/documentation/the-swift-programming-language/summaryofthegrammar

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Modifier, Accessor 23 import BypassAccessing struct Declaration { @BypassAccess @MainActor private init(_ arg: inout String) async throws where Element: Equatable {} #if DEBUG @MainActor static func ___init(_ arg: inout String) async throws -> Self where Element: Equatable { try await Self.init(_: &arg) } #endif }

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Limitation ● ❌ privateが現れるインターフェース ○ Method must be declared private because its parameter uses a private type ● ❌ 型推論を伴うプロパティ ○ 　 ○ '@BypassAccess' attribute require TypeAnnotation 24 @BypassAccess private var value = "value"

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Support Grammar ● 想定利用ケースは、テストを参照 ○ https://github.com/yutailang0119/swift-bypass-accessing/tree/main/Tests/BypassAccessingTests ● 考慮外パターンが存在しそう🫥 25

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小噺 ● SwiftSyntaxBuilder ○ 複雑だが、今回のケースでは便利 ■ 条件に応じて、Expressionを組み合わせ可能 ○ PlainTextで実装後、SyntaxBuilderで書き直した ● Macroのテストは swift-testing が使えない ○ XCTest ○ https://github.com/swiftlang/swift-syntax/issues/2720 26

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27 Conclusion

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Conclusion ● yutailang0119/swift-bypass-accessing ○ @BypassAccess ● 想定外を見つけたら、ご連絡ください📲 28

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29 Advertisement

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