Optional Extension Tips Kyobashi.swift #2 @horimislime

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Optionalͷ஍ຯͳπϥΈ

Objective-C if (users.count == 0) { // nil͔ۭͩͬͨΒԿ͔͢Δ } if (name.length == 0) { // ໊લ͕nil͔ۭͩͬͨΒԿ͔͢Δ }

Swift // Compile error ! if users?.isEmpty { // ... } if name?.isEmpty { // ... }

OptionalΛѻ͏ࡍͷ͓໿ଋ guard let users = users where !users.isEmpty else { // nil͔ۭͩͬͨΒԿ͔͢Δ }

Nil Coalescing • ୹͘ॻ͚Δ͕ɺͺͬͱݟͷՄಡੑʹ͚ܽΔ if array?.isEmpty ?? false { // ... } if !(str ?? "").isEmpty { // ... }

θϩ൑ఆ • nilͷൺֱ͸ৗʹfalse • Objective-C→Swiftʹࣸܦ͢Δͱ௧͍໨ʹ // Objective-C if (str.count == 0) { ... } /// Swift if str?.characters.count == 0 { ... }

໰୊ • ܕ͕ݫີʹͳͬͨ΋ͷͷɺʮۭʯͷѻ͍͕໘౗ • nilͱۭͷঢ়ଶΛಉ͡Α͏ʹѻ͏ʹ͸ʁ

Optional Extension • isNilOrEmptyతͳ΋ͷ • ௚઀Optionalʹextension͸ੜ΍ͤͳ͍ // Error: 'Wrapped' constrained to non-protocol type 'String' extension Optional where Wrapped: String { var isNilOrEmpty: Bool { return self?.isEmpty ?? true } }

Optional Extension • ಠࣗprotocolΛ༻ҙ͠ɺStringʹ४ڌͤ͞Δ protocol StringType { var isEmpty: Bool { get } } extension String: StringType {} extension Optional where Wrapped: StringType { var isNilOrEmpty: Bool { return self?.isEmpty ?? true } }

/// Before if name == nil || name.isEmpty else { // nil͔ۭͩͬͨΒԿ͔͢Δ } /// After if name.isNilOrEmpty { ... }

·ͱΊ • nilͱۭ͸ҰॹͰߟ͑Δ৔߹͕ଟ͍ • ஍ຯͳͱ͜ΖͰՄಡੑΛམͱ͞ͳ͍Ұ޻෉ • Objective-C͔ΒSwiftҠߦظʹ͋Δͱศར͔΋

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