Kotlin Null-Safety機構について

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Kotlin Null-Safetyػߏʹ͍ͭͯ 2013-11-09 JJUG CCC 2013 fall JVMݴޠύωϧσΟεΧογϣϯ ! ೔ຊKotlinϢʔβάϧʔϓ  ௕ᖒ ଠ࿠

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Α͋͘Δᷤ౻ • NullPointerException͕සൃ • NullνΣοΫ • ඞཁѱ

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Nullͱ্खʹ෇͖߹͏ํ๏ • ϝιουγάωνϟͷ޻෉ • ੩తղੳπʔϧ • ܕΛ࡞ͬͯϥοϓ

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ϝιουγάωνϟͷ޻෉ calc(String s) throws NPE! getNameOrNull()

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੩తղੳπʔϧ calc(@NotNull String s)! @NotNull String getName()

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ܕΛ࡞ͬͯϥοϓ calc(Optional s)! Optional getName()

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͵ΔΆ͸ۦஞͰ͖ͳ͍ calc(null);

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ͦ͜ͰKotlinͷ! Null-Safety

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Null-Safety • NotNull, NullableΛݴޠͰαϙʔτ • Φʔόϔουͳ͠ • Nullableʹ͸ͱ͜ͱΜ৻ॏʹͳΔ • Ͱ΋ॻ͖΍͢͞ɺಡΈ΍͢͞Λҡ࣋

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NotNull val name: String

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NotNull val name: String = null

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NotNull val name: String = null ίϯύΠϧΤϥʔʂ! ࣮ߦՄೳͳόΠτίʔυΛੜ·ͳ͍! ৗʹ҆৺ͯ͠ࢀরͰ͖Δ

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NotNull val name: String = null ίϯύΠϧΤϥʔʂ! ࣮ߦՄೳͳόΠτίʔυΛੜ·ͳ͍! ৗʹ҆৺ͯ͠ࢀরͰ͖Δ Null can not be a value of a non-null type jet.String

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Nullable val name: String? = null! name.toUpperCase()

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Nullable val name: String? = null! name.toUpperCase() ίϯύΠϧΤϥʔʂ! ෆ஫ҙʹΑΔNPEΛഉআ͢Δ

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NullνΣοΫٛ຿Խ val name: String? = null! if(name != null)! ! name.toUpperCase() ίϯύΠϧ௨Δ

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Safe Call ↓! if(name != null) name.toUpperCase()! else null val name: String? = null! name?.toUpperCase()

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Safe Call͸ศར val got = listOf(“foo”, null) map{! it?.toUpperCase()?.reverse()! }! ! assert(got == listOf(“OOF”, null))

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Safe Callͱ૬ੑͷྑ͍ػೳ val name =! (param[“name”] as? String)?.trim()! ! person.setName(name ?: “໊ແ͠”) Safe Cast Elvis operator

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NPE͕ൃੜ͢Δ৔໘ • throw NullPointerException()! • ֎෦Javaίʔυͷݺͼग़͠ • !!ԋࢉࢠͷ࢖༻

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͝ਗ਼ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠