読みやすいコードの書き方 第 5 回 / Code readability: Session 5 (ver. 2, Ja)

第 5 回: 関数

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セッションリスト

第 1 回: 導入と原則
- https://speakerdeck.com/munetoshi/code-readability-session-1-ver-2-ja

第 2 回: 命名
- https://speakerdeck.com/munetoshi/code-readability-session-2-ver-2-ja

第 3 回: コメント
- https://speakerdeck.com/munetoshi/code-readability-session-3-ver-2-ja

第 4 回: 状態
- https://speakerdeck.com/munetoshi/code-readability-session-4-ver-2-ja

第 5 回: 関数
- https://speakerdeck.com/munetoshi/code-readability-session-5-ver-2-ja

第 6 回: 依存関係 I
- https://speakerdeck.com/munetoshi/code-readability-session-6-ver-2-ja

第 7 回: 依存関係 II
- https://speakerdeck.com/munetoshi/code-readability-session-7-ver-2-ja

第 8 回: レビュー
- https://speakerdeck.com/munetoshi/code-readability-session-8-ver-2-ja

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関連書籍 「読みやすいコードのガイドライン - 持続可能なソフトウェア開発のために」
- https://gihyo.jp/book/2022/978-4-297-13036-7

英語版のリスト: https://gist.github.com/munetoshi/65a1b563fb2c271f328c121a4ac63571#file-code-readability-links-md

以前のバージョン (英語): https://speakerdeck.com/munetoshi/code-readability

© 2019-2023 Munetoshi Ishikawa, supported by LINE corporation

Transcript

1. abstract fun ಡΈ΍͍͢ίʔυͷॻ͖ํ(): ୈ 5 ճ
   fun ؔ਺()
   

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2. લճͷ͓͞Β͍: ঢ়ଶ
   ಡΈ΍͢͞ɾؤ݈ੑͷͨΊʹঢ়ଶΛ୯७Խ͢Δ
   - ୯७Խͦͷ΋ͷΛ໨తʹ͠ͳ͍
   ඇ௚ަͳؔ܎Λഉআ͢Δ
   - ؔ਺ʹΑΔஔ͖׵͑ɾ௚࿨ܕ΍ྻڍͷར༻
   ঢ়ଶભҠͷઃܭʹؾΛ഑Δ
   - ෆมɾႈ౳ɾ८ճ
   

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3. ߨٛͷߏ੒
   - ಋೖͱݪଇ
   - ࣗવݴޠ: ໋໊, ίϝϯτ
   - ܕͷߏ଄: ঢ়ଶ, ؔ਺
   - ܕؒͷߏ଄: ґଘؔ܎I, ґଘؔ܎II
   - ϨϏϡʔ
   ؔ਺ > ಋೖ
   

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4. ͜ͷߨٛʹ͓͚Δʮؔ਺ʯͷൣғ
   - αϒϧʔνϯ
   - ϓϩγʔδϟ
   - ϝιου
   - ίϯϐϡʔςουϓϩύςΟ
   - ίϯετϥΫλɾΠχγϟϥΠθʔγϣϯϒϩοΫ
   - ...
   ؔ਺ > ಋೖ
   

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5. ಡΈ΍͍ؔ͢਺ͱ͸
   ৼΔ෣͍͕༧ଌՄೳ
   - ໊લͱৼΔ෣͍ͷ੔߹ੑ͕͋Δ
   - Τϥʔέʔε΍੍໿͕গͳ͍
   - υΩϡϝϯςʔγϣϯ͕ॻ͖΍͍͢
   ؔ਺ > ಋೖ
   

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6. ؔ਺Λ༧ଌՄೳʹ͢ΔͨΊʹ
   ؔ਺ͷʮ੹೚ʯͱʮྲྀΕʯΛ໌֬ʹ͢Δ
   ؔ਺ > ಋೖ
   

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7. ࠓճͷ಺༰
   ੹೚Λ໌֬ʹ͢Δ
   - ཁ໿͠ʹ͍ؔ͘਺Λ෼ׂ͢Δ
   - ίϚϯυͱΫΤϦΛ෼ׂ͢Δ
   ྲྀΕΛ໌֬ʹ͢Δ
   - ఆٛࢦ޲ϓϩάϥϛϯάΛߦ͏
   - ϋοϐʔύεʹয఺Λ౰ͯΔ
   - ৚݅Ͱͳ͘ɺର৅Ͱ෼ׂ͢Δ
   ؔ਺ > ಋೖ
   

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8. ࠓճͷ಺༰
   ੹೚Λ໌֬ʹ͢Δ
   - ཁ໿͠ʹ͍ؔ͘਺Λ෼ׂ͢Δ
   - ίϚϯυͱΫΤϦΛ෼ׂ͢Δ
   ྲྀΕΛ໌֬ʹ͢Δ
   - ఆٛࢦ޲ϓϩάϥϛϯάΛߦ͏
   - ϋοϐʔύεʹয఺Λ౰ͯΔ
   - ৚݅Ͱͳ͘ɺର৅Ͱ෼ׂ͢Δ
   ؔ਺ > ੹೚ > ཁ໿ʹΑΔ֬ೝ
   

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9. ཁ໿͠ʹ͍ؔ͘਺Λ෼ׂ͢Δ
   ·ͣ͸ɺؔ਺ͷಈ࡞Λཁ໿ͯ͠ΈΔ
   ؔ਺ > ੹೚ > ཁ໿ʹΑΔ֬ೝ
   

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10. ؔ਺ͷཁ໿: ྫ 1/2
    ໰୊: ͜ͷίʔυΛͲͷΑ͏ʹཁ໿Ͱ͖Δʁ
    messageView.text = receivedMessageData.contentText
    senderNameView.text = receivedMessageData.senderName
    timestampView.text = receivedMessageData.sentTimeText
    ղ౴ྫ: "ड͚औͬͨϝοηʔδͰදࣔϨΠΞ΢τΛߋ৽͢Δ"
    ؔ਺ > ੹೚ > ཁ໿ʹΑΔ֬ೝ
    

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11. ؔ਺ͷཁ໿: ྫ 2/2
    ໰୊: ͜ͷίʔυΛͲͷΑ͏ʹཁ໿Ͱ͖Δʁ
    messageView.text = receivedMessageData.contentText
    doOnTransaction {
    messageDatabase.insertNewMessage(receivedMessageData)
    }
    ճ౴ྫʁ:
    "ϝοηʔδσʔλΛදࣔͨ͠ ޙʹɺอଘ͢Δ"
    "ϝοηʔδσʔλΛड͚औͬͨ ࣌ʹɺॲཧΛ͢Δ"
    ؔ਺ > ੹೚ > ཁ໿ʹΑΔ֬ೝ
    

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12. ؔ਺ͷ੹೚ͱཁ໿ͷؔ܎
    ཁ໿͕ॻ͖ʹ͍͘ = ؔ਺ͷ෼ׂ͕ඞཁ͔΋
    fun bindMessageViewData(messageData: MessageData) { ... }
    fun saveMessageDataToDatabase(messageData: MessageData) { ... }
    ྫ֎:
    - ଞϨΠϠ/Ϟδϡʔϧʹެ։͞ΕͨΠϯλʔϑΣΠε
    - ΠϕϯτॲཧͷΤϯτϦʔϙΠϯτ
    ؔ਺ > ੹೚ > ཁ໿ʹΑΔ֬ೝ
    

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13. ࠓճͷ಺༰
    ੹೚Λ໌֬ʹ͢Δ
    - ཁ໿͠ʹ͍ؔ͘਺Λ෼ׂ͢Δ
    - ίϚϯυͱΫΤϦΛ෼ׂ͢Δ
    ྲྀΕΛ໌֬ʹ͢Δ
    - ఆٛࢦ޲ϓϩάϥϛϯάΛߦ͏
    - ϋοϐʔύεʹয఺Λ౰ͯΔ
    - ৚݅Ͱͳ͘ɺର৅Ͱ෼ׂ͢Δ
    ؔ਺ > ੹೚ > ίϚϯυͱΫΤϦ
    

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14. ίϚϯυɾΫΤϦ෼཭ͷݪଇ6
    ؔ਺ΛʮίϚϯυʯͱʮΫΤϦʯͰ෼ׂ͢Δ
    - ίϚϯυ: Ϩγʔό΍Ҿ਺Λมߋ͢Δ
    - ΫΤϦ: มߋΛ൐Θͣʹ໭Γ஋Λฦ͢
    6 Bertrand Meyer. 1988. Object-oriented Software Construction. Prentice-Hall
    ؔ਺ > ੹೚ > ίϚϯυͱΫΤϦ
    

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15. ίϚϯυɾΫΤϦ෼཭ͷݪଇ: ྫ 1/2
    class IntList(vararg elements: Int) {
    infix fun append(others: IntList): IntList = ...
    }
    val a = IntList(1, 2)
    val b = IntList(3, 4)
    val c = a append b
    ໰୊: a, b, c ͷظ଴͞ΕΔ஋͸ʁ
    ؔ਺ > ੹೚ > ίϚϯυͱΫΤϦ
    

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16. ίϚϯυɾΫΤϦ෼཭ͷݪଇ: ྫ 2/2
    val a = IntList(1, 2)
    val b = IntList(3, 4)
    val c = a append b
    ௨ৗظ଴͞ΕΔ݁Ռ: a={1, 2}, b={3, 4}, c={1, 2, 3, 4}
    Α͘ͳ͍ಈ࡞ͷ݁Ռ: a={1, 2, 3, 4}, b={3, 4}, c={1, 2, 3, 4}
    append ؔ਺͸໭Γ஋Λ࣋ͭͷͰ a ΍ b Λมߋ͢΂͖Ͱ͸ͳ͍
    ؔ਺ > ੹೚ > ίϚϯυͱΫΤϦ
    

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17. ίϚϯυɾΫΤϦ෼཭ͷݪଇ: σϝϦοτ 1/3
    ίϚϯυɾΫΤϦͷ෼཭Λ໨తʹͯ͠͸ͳΒͳ͍
    - ΑΓڧ͍ґଘؔ܎ͷݪҼʹͳΓ͑Δ ʢ࣍ճͰৄࡉΛઆ໌ʣ
    - ෆཁͳঢ়ଶͷݪҼʹͳΓ͑Δ
    ؔ਺ > ੹೚ > ίϚϯυͱΫΤϦ
    

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18. ίϚϯυɾΫΤϦ෼཭ͷݪଇ: σϝϦοτ 2/3
    Α͘ͳ͍ίʔυͷྫ
    class UserDataStore {
    private var latestOperationResult: Result = NO_OPERATION
    // Command
    fun saveUserData(userData: UserData) = ...
    // Query
    val wasLatestOperationSuccessful: Boolean get() = ...
    }
    latestOperationResult ͕όάͷݪҼʹͳΔ
    ؔ਺ > ੹೚ > ίϚϯυͱΫΤϦ
    

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19. ίϚϯυɾΫΤϦ෼཭ͷݪଇ: σϝϦοτ 3/3
    Α͍ίʔυͷྫ
    class UserDataRequester {
    /**
    * Saves a given user data to ...
    * Then, returns true if the operation successful, otherwise false.
    */
    fun saveUserData(userData: UserData): Boolean = ...
    }
    ࠷ޙͷঢ়ଶΛฦ͢͜ͱͰɺอଘͷඞཁ͕ͳ͘ͳΔ
    ؔ਺ > ੹೚ > ίϚϯυͱΫΤϦ
    

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20. ίϚϯυɾΫΤϦͷ෼཭Λ͢Δ৚݅
    ʮϝΠϯͷʯ݁ՌΛฦ͢ͱ͖͸มߋ͠ͳ͍
    = ʮαϒͷʯ݁ՌΛฦ͢ͱ͖͸มߋΛ൐ͬͯΑ͍
    - ϝΠϯͷ݁Ռ: ม׵ɾܭࢉ݁Ռ, ৽͍͠Πϯελϯε ...
    - αϒͷ݁Ռ: Τϥʔ஋, มߋͷϝλσʔλʢετΞͨ͠αΠζʣ...
    (υΩϡϝϯςʔγϣϯ͕ඞਢ)
    σϑΝΫτελϯμʔυͱͳ͍ͬͯΔΠϯλʔϑΣΠε΋Մ
    ྫ: Queue.poll(): E, Iterator.next(): E
    ؔ਺ > ੹೚ > ίϚϯυͱΫΤϦ
    

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21. ੹೚Λ໌֬ʹ͢Δ: ·ͱΊ
    ཁ໿͕೉͍͠ͱ͖͸ؔ਺Λ෼཭ͯ͠ΈΔ
    - ·ͣ͸υΩϡϝϯςʔγϣϯΛॻ͍ͯΈΔ
    ʮϝΠϯͷʯ݁ՌΛฦ͢ͱ͖͸มߋ͠ͳ͍
    - ʮαϒͷʯ݁Ռͱมߋ͸ڞଘͯ͠Α͍
    - σϑΝΫτελϯμʔυͱͯ͠஌ΒΕΔΠϯλʔϑΣΠε΋Մ
    ؔ਺ > ੹೚ > ·ͱΊ
    

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22. ࠓճͷ಺༰
    ੹೚Λ໌֬ʹ͢Δ
    - ཁ໿͠ʹ͍ؔ͘਺Λ෼ׂ͢Δ
    - ίϚϯυͱΫΤϦΛ෼ׂ͢Δ
    ྲྀΕΛ໌֬ʹ͢Δ
    - ఆٛࢦ޲ϓϩάϥϛϯάΛߦ͏
    - ϋοϐʔύεʹয఺Λ౰ͯΔ
    - ৚݅Ͱͳ͘ɺର৅Ͱ෼ׂ͢Δ
    ؔ਺ > ྲྀΕ
    

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23. ྲྀΕ͕໌֬ͳؔ਺
    ͳͳΊಡΈͰಈ࡞͕೺ѲͰ͖Δ͜ͱ͕ॏཁ
    - ৄࡉΛಡΈඈ͹ͯ͠΋ཧղ͕Ͱ͖Δ
    - ॏཁͳίʔυͷ৔ॴ͕Θ͔Γ΍͍͢
    - ৚݅෼ذΛ໢ཏ͠ͳͯ͘΋Α͍
    ཁ໿Λॻ͘͜ͱͰ֬ೝͰ͖Δ
    ؔ਺ > ྲྀΕ
    

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24. ࠓճͷ಺༰
    ੹೚Λ໌֬ʹ͢Δ
    - ཁ໿͠ʹ͍ؔ͘਺Λ෼ׂ͢Δ
    - ίϚϯυͱΫΤϦΛ෼ׂ͢Δ
    ྲྀΕΛ໌֬ʹ͢Δ
    - ఆٛࢦ޲ϓϩάϥϛϯάΛߦ͏
    - ϋοϐʔύεʹয఺Λ౰ͯΔ
    - ৚݅Ͱͳ͘ɺର৅Ͱ෼ׂ͢Δ
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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25. ఆٛࢦ޲ϓϩάϥϛϯά 1/2
    Definition-based programming
    ໊લͷ͍ͭͨม਺΍ؔ਺Λଟ༻͢ΔϓϩάϥϛϯάελΠϧ
    ໨త:
    - ಡΈඈ͹ͤΔίʔυΛ໌֬ʹ͢Δ
    - ߴ͍ந৅౓Λ༩͑Δ
    - ಡΈฦ͠ΛݮΒ͢
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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26. ఆٛࢦ޲ϓϩάϥϛϯά 2/2
    ಡΈʹ͍͘ཁૉΛ ໊લͷ͍ͭͨม਺΍ؔ਺ Ͱஔ͖׵͑Δ
    ಡΈʹ͍͘ཁૉ:
    - ωετ (Ҿ਺ɾؔ਺ɾΫϥεɾ੍ޚߏ଄)
    - ແ໊ؔ਺ɾΦϒδΣΫτϦςϥϧ
    - ϝιουνΣΠϯ
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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27. Ҿ਺ͷωετ: ໰୊఺ 1/2
    ໰୊: ͳͥҎԼͷίʔυ͸ಡΈʹ͍͘ʁ
    showDialogOnError(
    presenter.updateSelfProfileView(
    repository.queryUserModel(userId)
    )
    )
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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28. Ҿ਺ͷωετ: ໰୊఺ 2/2
    ղ౴:
    - ॏཁͳؔ਺ݺͼग़͕͠ωετͷ಺ଆʹ͋Δ
    - ͢΂ͯͷ໭Γ஋Λཧղ͠ͳ͍ͱಈ࡞͕Θ͔Βͳ͍
    - ίʔυͷྲྀΕ͕ٯʢԼ͔Β্ʣʹͳ͍ͬͯΔ
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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29. Ҿ਺ͷωετ: मਖ਼ํ๏
    ໭Γ஋ʹ ໊લͷ͍ͭͨϩʔΧϧม਺ Λ࢖͏
    val userModel = repository.queryUserModel(userId)
    val viewUpdateResult =
    presenter.updateSelfProfileView(UserModel)
    showDialogOnError(viewUpdateResult)
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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30. ϥϜμΛ࢖͏ϝιουνΣΠϯ: ໰୊఺ 1/2
    ໰୊: ͜ͷίʔυͷಡΈʹ͍͘఺͸ʁ
    return queryTeamMemberIds(teamId)
    .map { memberId ->
    ... // Convert to UserModel
    ...
    }
    .filter {
    val userStatus = ...
    userStatus.isOnline
    }
    .map { it.emailAddress }
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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31. ϥϜμΛ࢖͏ϝιουνΣΠϯ: ໰୊఺ 2/2
    ղ౴:
    ҎԼͷ 2 ͭΛཧղ͠ͳ͍ͱಈ࡞͕Θ͔Βͳ͍
    - ֤ϝιουݺͼग़͠ͷϨγʔό (= ֤ݺͼग़͠ͷ໭Γ஋)
    - ϥϜμͷಈ࡞ͷৄࡉ
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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32. ϥϜμΛ࢖͏ϝιουνΣΠϯ: मਖ਼ํ๏ 1/2
    Ҋ1: ໊લͷ͍ͭͨϩʔΧϧม਺ ͰνΣΠϯΛ෼ׂ͢Δ
    val teamMembers = queryTeamMemberIds(teamId).map { ...
    ...
    }
    val onlineTeamMembers = teamMembers.filter { ...
    ...
    }
    return onlineTeamMembers.map { it.emailAddress }
    ϥϜμ͕௕͍ͱɺྲྀΕ͕ಡΈʹ͍͘Մೳੑ΋
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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33. ϥϜμΛ࢖͏ϝιουνΣΠϯ: मਖ਼ํ๏ 2/2
    Ҋ2: ໊લͷ͍ͭͨϓϥΠϕʔτؔ਺ ͰϥϜμΛஔ͖׵͑Δ
    return queryTeamMemberIds(teamId)
    .map(::toUserModel)
    .filter(::isOnline)
    .map { it.emailAddress }
    ...
    private fun toUserModel(userId: UserId): UserModel { ... }
    private fun isOnline(userModel: UserModel): Boolean { ... }
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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34. ఆٛࢦ޲ϓϩάϥϛϯά: མͱ݀͠
    நग़ʹΑͬͯίʔυ͕ಡΈʹ͘͘ͳΔ͜ͱ΋
    - ෆཁͳঢ়ଶ
    - ա৒ʹڧ͍ґଘؔ܎ ʢ࣍ճͰৄࡉΛઆ໌ʣ
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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35. நग़ͷམͱ݀͠: ΦϦδφϧͷίʔυ
    val userNameTextView: View = ...
    val profileImageView: View = ...
    init {
    // Complex userNameTextView initialization code
    userNameTextView...
    // Complex profileImageView initialization code
    profileImageView...
    }
    init ϒϩοΫ͕ංେԽͨͨ͠Ίநग़͢Δ
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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36. நग़ͷམͱ݀͠: ؒҧͬͨमਖ਼ํ๏
    var userNameTextView: View? = null
    var profileImageView: View? = null
    init {
    initializeUserNameTextView()
    initializeProfileImageView()
    }
    private fun initializeUserNameTextView() {
    userNameTextView = ...
    private fun initializeProfileImageView() {
    profileImageView = ...
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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37. நग़ͷམͱ݀͠: Կ͕ؒҧ͍͔ͬͯͨ
    - ෆཁͳՄมੑɾnullable
    - ෳ਺ճ initialize... ͕ݺ͹ΕΔՄೳੑ
    - ؔ਺໊ initialize... ͷᐆດੑ
    நग़͞ΕΔίʔυͷൣғΛ࠷దԽ͢Δ
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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38. நग़ͷམͱ݀͠: ਖ਼͍͠मਖ਼ํ๏
    Ϗϡʔͷੜ੒ɾॳظԽ෦෼ͷΈΛநग़͢Δ
    val userNameTextView: View = createUserNameTextView()
    val profileImageView: View = createProfileImageView()
    private fun createUserNameTextView(): TextView =
    ...
    private fun createProfileImageView(): ImageView =
    ...
    ؔ਺ > ྲྀΕ > ఆٛࢦ޲ϓϩάϥϛϯά
    

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39. ࠓճͷ಺༰
    ੹೚Λ໌֬ʹ͢Δ
    - ཁ໿͠ʹ͍ؔ͘਺Λ෼ׂ͢Δ
    - ίϚϯυͱΫΤϦΛ෼ׂ͢Δ
    ྲྀΕΛ໌֬ʹ͢Δ
    - ఆٛࢦ޲ϓϩάϥϛϯάΛߦ͏
    - ϋοϐʔύεʹয఺Λ౰ͯΔ
    - ৚݅Ͱͳ͘ɺର৅Ͱ෼ׂ͢Δ
    ؔ਺ > ྲྀΕ > ϋοϐʔύεʹয఺Λ౰ͯΔ
    

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40. ϋοϐʔύεͱΞϯϋοϐʔύε
    ϋοϐʔύε: ؔ਺ͷओͳ໨తΛୡ੒͢Δέʔε
    Ξϯϋοϐʔύε: ؔ਺ͷओͳ໨తΛୡ੒ͤͣʹऴྃ͢Δέʔε
    ؔ਺ > ྲྀΕ > ϋοϐʔύεʹয఺Λ౰ͯΔ
    

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41. ϋοϐʔύεͱΞϯϋοϐʔύε: ྫ
    String.toIntOrNull()
    ϋοϐʔύε: ੔਺Λฦ͢
    e.g, "-1234", "0", "+001", "-2147483648"
    Ξϯϋοϐʔύε: null Λฦ͢
    e.g., "--0", "text", "", "2147483648", "1.0"
    ؔ਺ > ྲྀΕ > ϋοϐʔύεʹয఺Λ౰ͯΔ
    

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42. ؔ਺ͷྲྀΕͱϋοϐʔύεɾΞϯϋοϐʔύε
    ઌʹΞϯϋοϐʔύεΛআ֎͠ɺϋοϐʔύεʹয఺Λ͋ͯΔ
    ʮΞʔϦʔϦλʔϯʯΛద༻͢Δ
    ؔ਺ > ྲྀΕ > ϋοϐʔύεʹয఺Λ౰ͯΔ
    

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43. ΞʔϦʔϦλʔϯ: Α͘ͳ͍ྫ
    if (isNetworkAvailable()) {
    val queryResult = queryToServer()
    if (queryResult.isValid) {
    // Do something with queryResult...
    } else {
    showInvalidResponseDialog()
    }
    } else {
    showNetworkUnavailableDialog()
    }
    ؔ਺ > ྲྀΕ > ϋοϐʔύεʹয఺Λ౰ͯΔ
    

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44. ΞʔϦʔϦλʔϯ: Կ͕ʮΑ͘ͳ͍ʯ͔
    ෆ໌ྎ
    - Ͳ͜ʹॏཁͳίʔυ͕͋Δ͔͕Θ͔Γʹ͍͘
    - Τϥʔ৚݅ͱͦͷॲཧͷؔ࿈ੑ͕Θ͔Γʹ͍͘
    ؔ਺ > ྲྀΕ > ϋοϐʔύεʹয఺Λ౰ͯΔ
    

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45. ΞʔϦʔϦλʔϯ: Α͍ྫ
    if (!isNetworkAvailable()) {
    showNetworkUnavailableDialog()
    return
    }
    val queryResult = queryToServer()
    if (!queryResult.isValid) {
    showInvalidResponseDialog()
    return
    }
    // Do something with queryResult...
    ؔ਺ > ྲྀΕ > ϋοϐʔύεʹয఺Λ౰ͯΔ
    

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46. ΞʔϦʔϦλʔϯ: ஫ҙ఺ 1/2
    when ΍ switch ͷҰ෦ͷ෼ذͰͷϦλʔϯΛආ͚Δ
    ΞʔϦʔϦλʔϯࣗମ΍ͦͷ৚݅Λݟམͱ͢Մೳੑ͕͋Δ
    val messageText = when (type) {
    FOO -> "this is FOO"
    BAR -> "this is BAR"
    null -> return
    }
    ؔ਺ > ྲྀΕ > ϋοϐʔύεʹয఺Λ౰ͯΔ
    

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47. ΞʔϦʔϦλʔϯ: ஫ҙ఺ 1/2
    when ΍ switch ͷҰ෦ͷ෼ذͰͷϦλʔϯΛආ͚Δ
    ΞʔϦʔϦλʔϯࣗମ΍ͦͷ৚݅Λݟམͱ͢Մೳੑ͕͋Δ
    if (type == null) {
    return
    }
    val messageText = when (type) {
    FOO -> "this is FOO"
    BAR -> "this is BAR"
    }
    ؔ਺ > ྲྀΕ > ϋοϐʔύεʹয఺Λ౰ͯΔ
    

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48. ΞʔϦʔϦλʔϯ: ஫ҙ఺ 2/2
    ෆཁͳΞϯϋοϐʔύεΛ࡞Βͳ͍Α͏ʹ͢Δ
    యܕతͳྫ: ۭͷίϨΫγϣϯʹର͢Δ૸ࠪ
    if (list.isEmpty) {
    return listOf()
    }
    return list
    .filter { ... }
    .map { ... }
    ؔ਺ > ྲྀΕ > ϋοϐʔύεʹয఺Λ౰ͯΔ
    

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49. ࠓճͷ಺༰
    ੹೚Λ໌֬ʹ͢Δ
    - ཁ໿͠ʹ͍ؔ͘਺Λ෼ׂ͢Δ
    - ίϚϯυͱΫΤϦΛ෼ׂ͢Δ
    ྲྀΕΛ໌֬ʹ͢Δ
    - ఆٛࢦ޲ϓϩάϥϛϯάΛߦ͏
    - ϋοϐʔύεʹয఺Λ౰ͯΔ
    - ৚݅Ͱͳ͘ɺର৅Ͱ෼ׂ͢Δ
    ؔ਺ > ྲྀΕ > ର৅ʹΑΔ෼ׂ
    

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50. ؔ਺Λ෼ׂ͢Δ࣠ 1/2
    ؔ਺Λ෼ׂ͢Δͱ͖ɺෳ਺ͷ෼͚ํ͕͋Δ
    ྫ: ΞΧ΢ϯτͷঢ়ଶΛදࣔ͢Δ
    - ৚݅: ΞΧ΢ϯτͷλΠϓ (premium, free)
    - ର৅: දࣔ͢ΔϏϡʔ (background, icon)
    ؔ਺ > ྲྀΕ > ର৅ʹΑΔ෼ׂ
    

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51. ؔ਺Λ෼ׂ͢Δ࣠ 2/2
    ໰୊: ͲͪΒͷ࣠Ͱؔ਺Λ෼ׂ͢Δ΂͖ʁ
    Condition
    Object
    Premium account Free account
    Background color
    Account icon
    Red Gray
    “Twemoji” ©Twitter, Inc and other contributors (Licensed under CC-BY 4.0) https://twemoji.twitter.com/
    ؔ਺ > ྲྀΕ > ର৅ʹΑΔ෼ׂ
    

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52. ৚݅Ͱ෼ׂͨ͠৔߹ʢΑ͘ͳ͍ྫʣ
    fun bindViewData(accountType: AccountType) {
    when (accountType) {
    PREMIUM -> updateViewsForPremium()
    FREE -> updateViewsForFree()
    }
    }
    private fun updateViewsForPremium() {
    backgroundView.color = PREMIUM_BACKGROUND_COLOR
    accountTypeIcon.image = resources.getImage(PREMIUM_IMAGE_ID)
    }
    ؔ਺ > ྲྀΕ > ର৅ʹΑΔ෼ׂ
    

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53. ৚݅ʹΑΔ෼ׂ͕ͳͥʮΑ͘ͳ͍ʯ͔ 1/2
    യવͱͨ͠ཁ໿͔͠ॻ͚ͳ͍
    /**
    * Updates views depending whether the account type is free or premium.
    */
    ؔ਺ > ྲྀΕ > ର৅ʹΑΔ෼ׂ
    

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54. ৚݅ʹΑΔ෼ׂ͕ͳͥʮΑ͘ͳ͍ʯ͔ 2/2
    ৚݅ͱର৅ͷ૊Έ߹Θͤͷ໢ཏੑΛอূͰ͖ͳ͍
    when (accountType) {
    PREMIUM -> updateViewsForPremium()
    FREE -> updateViewsForFree()
    BUSINESS -> updateViewsForBusiness()
    }
    private fun updateViewsForBusiness() {
    backgroundView.color = PREMIUM_BACKGROUND_COLOR
    // [BUG] Forgot to update the account icon
    ؔ਺ > ྲྀΕ > ର৅ʹΑΔ෼ׂ
    

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55. ର৅ʹΑΔ෼ׂ: Α͍ྫ 1/2
    fun bindViewData(accountType: AccountType) {
    updateBackgroundViewColor(accountType)
    updateAccountTypeImage(accountType)
    }
    private fun updateBackgroundViewColor(accountType: AccountType) {
    backgroundView.color = when (accountType) {
    PREMIUM -> PREMIUM_BACKGROUND_COLOR
    FREE -> FREE_BACKGROUND_COLOR
    }
    }
    ؔ਺ > ྲྀΕ > ର৅ʹΑΔ෼ׂ
    

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56. ର৅ʹΑΔ෼ׂ: Α͍ྫ 2/2
    ۩ମతͳཁ໿͕ॻ͖΍͍͢
    /**
    * Updates background color and icon according to a given account type.
    */
    ৚݅ͱର৅ͷ૊Έ߹Θͤͷ໢ཏੑΛอূͰ͖Δ
    ߋͳΔϦϑΝΫλϦϯάΛద༻Ͱ͖Δ
    ྫ: நग़ͨؔ͠਺Λࢀরಁաʹ͢Δ
    ؔ਺ > ྲྀΕ > ର৅ʹΑΔ෼ׂ
    

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57. ର৅ʹΑΔ෼ׂ: ߋͳΔϦϑΝΫλϦϯά
    fun bindViewData(accountType: AccountType) {
    backgroundView.color = getBackgroundColorInt(accountType)
    accountTypeIcon.image = getAccountTypeIconImage(accountType)
    }
    private fun getBackgroundColorInt(accountType: AccountType): Int =
    when (accountType) {
    PREMIUM -> PREMIUM_BACKGROUND_COLOR
    FREE -> FREE_BACKGROUND_COLOR
    }
    ؔ਺ > ྲྀΕ > ର৅ʹΑΔ෼ׂ
    

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58. ΞʔϦʔϦλʔϯ VS ର৅ʹΑΔ෼ׂ
    ʮΞʔϦʔϦλʔϯʯ͸ʮ৚݅ʹΑΔ෼ׂʯͰ͸ʁ
    ઓུ 1:
    - ΞϯϋοϐʔύεΛϋοϐʔύεʹؚΊΔ
    ઓུ 2:
    - ઌʹΞʔϦʔϦλʔϯΛద༻͢Δ
    - ࢒ͬͨϋοϐʔύεʹରͯ͠ର৅ʹΑΔ෼ׂΛద༻͢Δ
    ؔ਺ > ྲྀΕ > ର৅ʹΑΔ෼ׂ
    

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59. ྲྀΕΛ໌֬ʹ͢Δ: ·ͱΊ
    ఆٛࢦ޲ϓϩάϥϛϯάΛߦ͏:
    ωετɾνΣΠϯɾϦςϥϧʹ໊લΛ͚ͭΔ
    ϋοϐʔύεʹয఺Λ౰ͯΔ:
    ΞʔϦʔϦλʔϯΛద༻͢Δ
    ৚݅Ͱͳ͘ɺର৅Ͱ෼ׂ͢Δ:
    ର৅͝ͱʹؔ਺΍ίʔυϒϩοΫΛͭ͘Δ
    ؔ਺ > ྲྀΕ > ·ͱΊ
    

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60. ·ͱΊ
    ཁ໿Λॻ͍ͯؔ਺͕ཧղ͠΍͍͔֬͢ೝ͢Δ
    ؔ਺ͷ੹೚:
    - ඞཁͳΒ෼ׂ͢Δ
    - ϝΠϯͷ݁ՌΛฦ͢ͱ͖͸มߋ͠ͳ͍
    ؔ਺ͷྲྀΕ:
    - ͳͳΊಡΈͰ͖ΔΑ͏ʹ͢Δ
    ؔ਺ > ·ͱΊ
    

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