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<String> s)! Optional<String> 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·ͨ͠