Kotlin Null-Safety機構について

JJUG CCC 2013 Fallで発表した資料

1. Kotlin Null-Safetyػߏʹ͍ͭͯ 2013-11-09 JJUG CCC 2013 fall JVMݴޠύωϧσΟεΧογϣϯ ! ೔ຊKotlinϢʔβάϧʔϓ
 ௕ᖒ ଠ࿠
2. Α͋͘Δᷤ౻ • NullPointerException͕සൃ • NullνΣοΫ • ඞཁѱ
3. Nullͱ্खʹ෇͖߹͏ํ๏ • ϝιουγάωνϟͷ޻෉ • ੩తղੳπʔϧ • ܕΛ࡞ͬͯϥοϓ
4. ϝιουγάωνϟͷ޻෉ calc(String s) throws NPE! getNameOrNull()
5. ੩తղੳπʔϧ calc(@NotNull String s)! @NotNull String getName()
6. ܕΛ࡞ͬͯϥοϓ calc(Optional<String> s)! Optional<String> getName()
7. ͵ΔΆ͸ۦஞͰ͖ͳ͍ calc(null);
8. ͦ͜ͰKotlinͷ! Null-Safety
9. Null-Safety • NotNull, NullableΛݴޠͰαϙʔτ • Φʔόϔουͳ͠ • Nullableʹ͸ͱ͜ͱΜ৻ॏʹͳΔ • Ͱ΋ॻ͖΍͢͞ɺಡΈ΍͢͞Λҡ࣋
10. NotNull val name: String
11. NotNull val name: String = null
12. NotNull val name: String = null ίϯύΠϧΤϥʔʂ! ࣮ߦՄೳͳόΠτίʔυΛੜ·ͳ͍! ৗʹ҆৺ͯ͠ࢀরͰ͖Δ
13. NotNull val name: String = null ίϯύΠϧΤϥʔʂ! ࣮ߦՄೳͳόΠτίʔυΛੜ·ͳ͍! ৗʹ҆৺ͯ͠ࢀরͰ͖Δ Null can not be a value of a non-null type jet.String
14. Nullable val name: String? = null! name.toUpperCase()
15. Nullable val name: String? = null! name.toUpperCase() ίϯύΠϧΤϥʔʂ! ෆ஫ҙʹΑΔNPEΛഉআ͢Δ
16. NullνΣοΫٛ຿Խ val name: String? = null! if(name != null)! ! name.toUpperCase() ίϯύΠϧ௨Δ
17. Safe Call ↓! if(name != null) name.toUpperCase()! else null val name: String? = null! name?.toUpperCase()
18. Safe Call͸ศར val got = listOf(“foo”, null) map{! it?.toUpperCase()?.reverse()! }! ! assert(got == listOf(“OOF”, null))
19. Safe Callͱ૬ੑͷྑ͍ػೳ val name =! (param[“name”] as? String)?.trim()! ! person.setName(name ?: “໊ແ͠”) Safe Cast Elvis operator
20. NPE͕ൃੜ͢Δ৔໘ • throw NullPointerException()! • ֎෦Javaίʔυͷݺͼग़͠ • !!ԋࢉࢠͷ࢖༻
21. ͝ਗ਼ௌ͋Γ͕ͱ͏͍͟͝·ͨ͠