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Swi$ 6ͷTyped throwsͱ
Swi$ʹ͓͚ΔΤϥʔϋϯυϦϯά
ͷશମ૾ΛֶͿ
@koher
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!LPIFS
J04%$+BQBOࢀՃྺ
2016:ෆࢀՃ
2017:۩ମྫͱΫΠζͰֶͿɺ4XJGUͷछྨͷΤϥʔͷ͍͚
2018:J04ΤϯδχΞͷͨΊͷɺ4XJGU͔Β1ZUIPOͷϥΠϒϥϦΛͬͯػցֶश͢Δํ๏
2019:)FBSUPG4XJGU
2020:ਓͰΞϓϦΛϦϑΝΫλϦϯάͯ͠ݟ͖͑ͯͨɺ࠷ڧͷJ04ΞϓϦઃܭʹٻΊΒΕΔ͜ͱ
2021:BTZODBXBJUBDUPSͰJ04ΞϓϦ։ൃ͕Ͳ͏มΘΔ͔#FGPSF"GUFSͷ۩ମྫͰֶͿ
2022:4XJGU$PODVSSFODZ࣌ͷJ04ΞϓϦͷ࡞Γํ
2023:"*࣌ʹੜ͖ΔJ04ΤϯδχΞͷา͖ํ
⛔3FKFDUFE
2024:4XJGUͷ5ZQFEUISPXTͱ4XJGUʹ͓͚ΔΤϥʔϋϯυϦϯάͷશମ૾ΛֶͿ
˞
ఏग़ͨ͠ϓϩϙʔβϧͷʢGPSUFFʹه͕ͳ͘ਖ਼֬ͳෆ໌ʣ
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Heart of Swift
!LPIFS
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ࠓ͢༰
!
Typed throws
!
Swi%ͷΤϥʔϋϯυϦϯάͷશମ૾
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!
Typed Throws
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SE-0413: Typed throws1
• Status: Implemented (Swi3 6.0)
1 h$ps:/
/github.com/swi3lang/swi3-evolu:on/blob/main/proposals/0413-typed-throws.md
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Untyped throws
func parseInt(_ value: String) throws -> Int
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Untyped throws
func parseInt(_ value: String) throws -> Int
try parseInt("") // ۭจࣈྻ
try parseInt("ABC") // ෆਖ਼ͳϑΥʔϚοτ
try parseInt("9999999999999999999") // ൣғ֎
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Untyped throws
enum ParseError: Error {
case emptyValue
case illegalFormat(String)
case outOfBounds(String)
}
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Untyped throws
func parseInt(_ value: String) throws -> Int {
if value.isEmpty { throw ParseError.emptyValue }
guard let number = Int(value) else {
if value.contains(/^[-]?\d+$/) {
throw ParseError.outOfBounds(value)
} else {
throw ParseError.illegalFormat(value)
}
}
return number
}
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Untyped throws
do {
let number = try parseInt(string)
print(number)
} catch {
print(error) // any Error
}
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Untyped throws
do {
let number: Int = try parseInt(string)
print(number)
} catch let error as ParseError {
switch error { // ParseError
case .emptyValue: ...
case .illegalFormat(let value): ...
case .outOfBounds(let value): ...
}
}
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⛔
Errors thrown from here are not handled
because the enclosing catch is not exhaus6ve
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Untyped throws
do {
let number: Int = try parseInt(string)
print(number)
} catch let error as ParseError {
switch error { // ParseError
case .emptyValue: ...
case .illegalFormat(let value): ...
case .outOfBounds(let value): ...
}
}
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Untyped throws
do {
let number: Int = try parseInt(string)
print(number)
} catch let error as ParseError {
switch error { // ParseError
case .emptyValue: ...
case .illegalFormat(let value): ...
case .outOfBounds(let value): ...
}
} catch {
preconditionFailure("Never reaches here.")
}
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Untyped throws
func parseInt(_ value: String) throws -> Int
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Typed throws
func parseInt(_ value: String) throws(ParseError) ->
Int
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Untyped throws
do {
let number = try parseInt(string)
print(number)
} catch {
print(error) // any Error
}
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Typed throws
do {
let number = try parseInt(string)
print(number)
} catch {
switch error { // ParseError
...
}
}
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Untyped throws
do {
let number: Int = try parseInt(string)
print(number)
} catch let error as ParseError {
switch error { // ParseError
case .emptyValue: ...
case .illegalFormat(let value): ...
case .outOfBounds(let value): ...
}
} catch {
preconditionFailure("Never reaches here.")
}
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Typed throws
do {
let number: Int = try parseInt(string)
print(number)
} catch {
switch error { // ParseError
case .emptyValue: ...
case .illegalFormat(let value): ...
case .outOfBounds(let value): ...
}
}
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Typed throws͕΄͔ͬͨ͠ଞͷཧ༝
func foo() throws -> Int { // any Error
let result: Result = ...
switch result {
case .success(let value):
return value
case .failure(let error):
throw error // FooError
}
}
• Result, Task ͱͷมͰΤϥʔͷܕ͕ࣦΘΕΔ
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Typed throwsؔ࿈ͷߏจ
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Typed throws
throws(Τϥʔܕ) -> Γܕ
• () ඞਢ
• () ͷதʹΤϥʔܕҰ͔ͭ͠ॻ͚ͳ͍
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SE-0413: Typed throws1
• Status: Implemented (Swi3 6.0)
• Alterna:ves considered
• Thrown error type syntax
1 h$ps:/
/github.com/swi3lang/swi3-evolu:on/blob/main/proposals/0413-typed-throws.md
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͠ () ͕ඞਢͰͳ͔ͬͨΒ
func foo() throws (E) -> Int { ... }
• ͲͪΒͱղऍ͢Εྑ͍͔ᐆດ
• throws E
• throws ((E) -> Int)
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͠ () ͕ඞਢͰͳ͔ͬͨΒ
func foo() throws bar -> Int { ... }
struct bar: Error {}
• bar ͕ܕ͔effect͔۠ผͰ͖ͳ͍
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SE-0413: Typed throws1
• Status: Implemented (Swi3 6.0)
• Alterna:ves considered
• Mul:ple thrown error types
1 h$ps:/
/github.com/swi3lang/swi3-evolu:on/blob/main/proposals/0413-typed-throws.md
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͠ () ͷதʹෳͷΤϥʔܕΛॻ͚ͨΒ
func foo() throws(BarError, BazError) -> Int
• BarError | BazError Λಋೖ͢Δͷͱಉ͡
• Typed throwsͷͨΊʹΔʹܕγεςϜͷӨڹ͕େ͖͢
͗Δ
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ݸਓతʹΤϥʔܕҰͭͰྑ͍ͱࢥ͏
• ΤϥʔܕΛෳࢦఆͰ͖Δͱɺ҆қʹԼͷΤϥʔΛͦͷ··
throw ͕ͪ͠
func foo() throws(IOError, NetworkError, ...) -> Int
• Τϥʔͷܕ͕ҰͭͳΒɺͦͷؔʹͱͬͯͷΤϥʔͱԿ͔Λ
ߟ͑Δ͖͔͚ͬʹͳΔ
• ԼͷΤϥʔΛͦͷ·· throw ͢ΔͳΒ any Error Ͱྑ͍
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Typed throws
throws(Τϥʔܕ) -> Γܕ
• () ඞਢ
• () ͷதʹΤϥʔܕҰ͔ͭ͠ॻ͚ͳ͍
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do
do {
let number = try parseInt(string) // ParseError
print(number)
} catch {
// ParseError
}
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do
do {
let number = try parseInt(string) // ParseError
try foo(number) // FooError
} catch {
// ???
}
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do
do {
let number = try parseInt(string) // ParseError
try foo(number) // FooError
} catch {
// any Error
}
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do throws
do throws(ParseError) {
let number = try parseInt(string) // ParseError
try foo(number) //
⛔
FooError
} catch {
// ParseError
}
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throws(any Error)
func foo() throws(any Error) -> Int
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throws(any Error)
func foo() throws(any Error) -> Int
func foo() throws -> Int // ͜Εͱಉ͡
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throws(Never)
func foo() throws(Never) -> Int
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throws(Never)
func foo() throws(Never) -> Int
func foo() -> Int // ͜Εͱಉ͡
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Result.get
// Swift 5
enum Result {
func get() throws -> Success
}
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Result.get
// Swift 6
enum Result {
func get() throws(Failure) -> Success
}
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Result.get
// Swift 5
let result: Result = ...
do {
let value = try result.get()
} catch {
preconditionFailure("Never reaches here.")
}
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Result.get
// Swift 6
let result: Result = ...
let value = result.get()
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rethrows
// try͕ෆཁ
[2, 3, 5].map { $0 * $0 }
// try͕ඞཁ
try ["2", "3", "5"].map { try parseInt($0) }
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rethrows
extension Sequence {
func map(
_ transform: (Element) throws -> T
) rethrows -> [T]
}
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rethrows
extension Sequence {
func map(
_ transform: (Element) throws -> T
) rethrows -> [T]
// rethrows↓ͷೋͭͱಉ͡Α͏ͳͷ
func map(_ transform: (Element) -> T) -> [T]
func map(
_ transform: (Element) throws -> T
) throws -> [T]
}
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rethrows
// try͕ෆཁ
[2, 3, 5].map { $0 * $0 }
// try͕ඞཁ
try ["2", "3", "5"].map { try parseInt($0) }
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rethrows
extension Sequence {
func map(
_ transform: (Element) throws -> T
) rethrows -> [T]
}
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Typed throwsʹΑΔ rethrows
extension Sequence {
func map(
_ transform: (Element) throws(E) -> T
) throws(E) -> [T]
}
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Typed throws҆қʹ͏͖Ͱͳ͍
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SE-0413: Typed throws1
• Status: Implemented (Swi3 6.0)
• When to use typed throws
• Typed throwsΛ҆қʹ͏͖Ͱͳ͍ཧ༝
• Ͳ͏͍͏ͱ͖ʹTyped throwsΛ͏͖͔
1 h$ps:/
/github.com/swi3lang/swi3-evolu:on/blob/main/proposals/0413-typed-throws.md
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Typed throwsΛ҆қʹ͏͖Ͱͳ͍ཧ༝
• ΤϥʔͷܕมԽ͍͢͠
• Τϥʔ͕ཏతʹϋϯυϦϯά͞ΕΔ͜ͱগͳ͍
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Ͳ͏͍͏ͱ͖ʹTyped throwsΛ͏͖͔
• Ϟδϡʔϧύοέʔδͷதʹดͯ͡ΤϥʔϋϯυϦϯά͢Δ
Α͏ͳ߹
• map ͷ rethrows Result ͷΑ͏ʹͦΕࣗମ͕ΤϥʔΛੜΈ
ग़͞ͳ͍߹
• Existen*al͕͑ͳ͍ʗΦʔόʔϔου͕ڐ༰Ͱ͖ͳ͍߹
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Resist the tempta+on to use typed throws1
Typed throwsΛ͏༠ʹ߅͍ͯͩ͘͠͞
1 h$ps:/
/github.com/swi3lang/swi3-evolu:on/blob/main/proposals/0413-typed-throws.md
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Even with the introduc/on of typed throws
into Swi5, the exis/ng (untyped) throws
remains the be>er default error-handling
mechanism for most Swi5 code.1
typed throws͕Swi.ʹಋೖ͞Εͨͱͯ͠ɺطଘͷʢuntypedʣ
throwsɺ΄ͱΜͲͷSwi.ίʔυʹ͓͍ͯɺґવͱͯ͠ΑΓྑ͍
σϑΥϧτͷΤϥʔϋϯυϦϯάϝΧχζϜͰ͢ɻ
1 h$ps:/
/github.com/swi3lang/swi3-evolu:on/blob/main/proposals/0413-typed-throws.md
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ݸਓతʹϞδϡʔϧύοέʔδΛӽ͑ͯྑ͍ͱࢥ͏
• ϞϊϨϙͳͲίʔυ͕Ұମͱͯ͠ཧ͞Ε͍ͯΔͱ͖
• ҾΓͷܕͱಉఔͷසͰ͔͠Τϥʔܕͷมߋ͕ى͜
Βͳ͍ͱ͖
• Result ͷ Failure ͱมΘΒͳ͍
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ͱ͍͑ɺTyped Throws͕׆͖Δέʔεݶఆత
• async ͷͱ͖͍ͮΒ͍
• CancellationError ͱͲ͏ڞଘ͢Δʁ
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Typed throwsͷΞϯνύλʔϯ
enum AppError {
case network(NetworkError)
case server(ServerError)
case cancellation(CancellationError)
}
•
⛔
Typed throwsʹ͢ΔͨΊʹ CancellationError Λ case
ʹՃ͑ΔͳͲɺSwi0ͷඪ४తͳΤϥʔϋϯυϦϯάͷ׳ྫͱઓ
͏
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Typed throwsͷΞϯνύλʔϯ
func foo() throws { // any Error
try bar() // AppError
try baz() // OtherError
}
do {
try foo()
} catch is CancellationError {
// Ωϟϯηϧ͞Εͨ߹ͷॲཧ
} catch {
//
⛔
AppError.calcellation͕ͬͪ͜ʹؚ·ΕΔ
}
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!
Swi%ͷΤϥʔϋϯυϦϯάͷ
શମ૾
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Error Handling Ra-onale and Proposal5
• Kinds of error
• Propaga0on
5 h$ps:/
/github.com/swi3lang/swi3/blob/main/docs/ErrorHandlingRa
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Kinds of error
• Simple domain errors
• Recoverable errors
• Universal errors
• Logic failures
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Simple domain errors
guard let number = Int(string) else {
// ΤϥʔϋϯυϦϯά
}
• ൃੜ͕݅໌֬Ͱ͙͢ʹϋϯυϦϯά͞ΕΔΑ͏ͳΤϥʔ
• Τϥʔͷཧ༝͕໌֬ͳͷͰ nil Ͱද͞ΕΔ
• ͙͢ʹϋϯυϦϯά͠ͳ͍ͱݪҼෆ໌ʹ
• ϋϯυϦϯά݅ذͰे
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Simple domain errors
guard let last = array.popLast() else {
// ΤϥʔϋϯυϦϯά
}
guard let max = array.max() else {
// ΤϥʔϋϯυϦϯά
}
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Recoverable errors
do {
try data.write(to: url, options: .atomic)
} catch {
// ΤϥʔϋϯυϦϯά
}
• ݪҼ͕ଟذʹΔΤϥʔͰ Error Ͱද͞ΕΔ
• దͳॴ·ͰΤϥʔΛͤ͞ݪҼʹԠͯ͡ϋϯυϦϯά
• ઐ༻ͷߏจʢ throws do/try/catch ʣ͕΄͍͠
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Universal errors
Array(repeating: 42, count: .max) // Out of memory
• ݪҼͱͳΔՕॴ͕ଟ༷Ͱ͋ΒΏΔՕॴͰى͜ΓಘΔΤϥʔ
• ϓϩηεͷதஅɾϝϞϦෆɾελοΫΦʔόʔϑϩʔͳͲ
• ݱঢ়Ͱඪ४తͳํ๏ͰϋϯυϦϯά͢Δ͜ͱͰ͖ͳ͍
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Logic failures
nilValue! // Unexpectedly found nil while unwrapping
array[-1] // Index out of bounds
Int.max + 1 // Overflow
• ίʔυͷޡΓ͕ݪҼͰൃੜ͢ΔΤϥʔ
• Forced unwrappingͷࣦഊɾΠϯσοΫεൣғ֎ɾͷΦʔ
όʔϑϩʔͳͲͷࣄલ݅ҧͳͲ
• ಈతʹϋϯυϦϯά͢ΔͷͰͳ͘ίʔυΛमਖ਼ͯ͠ରԠ
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Logic failures
func foo(length: Int) {
precondition(length >= 0)
...
}
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Logic failures
do {
let number: Int = try parseInt(string)
print(number)
} catch let error as ParseError {
switch error { // ParseError
case .emptyValue: ...
case .illegalFormat(let value): ...
case .outOfBounds(let value): ...
}
} catch {
preconditionFailure("Never reaches here.")
}
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Simple domain errors / Recoverable errors
vs
Logic failures
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Simple domain errors vs Logic failures
// Simple domain errors
dictionary[key] // ࣦഊ͢Δͱnil
// Logic failures
array[i] // ࣦഊ͢Δͱ࣮ߦ࣌Τϥʔ
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Ͳ͏ͯ͠ array[i]
ൣғ֎ͷͱ͖ʹ nil Λฦ͞ͳ͍ͷ͔ʁ
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array[i] ͕ൣғ֎ʹͳΔଟ͘ͷέʔείʔυͷޡΓ
// i, j͕ൣғ֎ʹͳͬͨ͜ͱ͕Θ͔࣮ͬͯߦ࣌ʹͰ͖Δ͜ͱͳ͍
func sort(_ array: inout [Int]) {
for i in 0 ..< array.count {
for j in i + 1 ..< array.count {
if array[j] < array[i] {
let t = array[j]
array[j] = array[i]
array[i] = t
}
}
}
}
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Logic failureͰྑ͍ͷΛ
Logic failureͱͯ͠ѻ͏͜ͱ͕ॏཁ
ʢRecoverableʹ͠ͳ͍ʣ
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optional! array[i] มΘΒͳ͍
• ͲͪΒLogic failure
• Forced unwrappingΛઈରʹආ͚ΔͳΒ array[i] ආ͚ͳ͍
ͱ߹ੑ͕औΕͳ͍
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optional! array[i] มΘΒͳ͍
let value = Int(string)!
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optional! array[i] มΘΒͳ͍
guard let value = Int(string) else {
predonditionFailure(...)
}
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optional! array[i] มΘΒͳ͍
let value = array[0]
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optional! array[i] มΘΒͳ͍
guard let value = array.first else {
predonditionFailure(...)
}
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Kinds of error
• Simple domain errors
• Recoverable errors
• Universal errors
• Logic failures
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Propaga'on
• Manual propaga,on
• Automa,c propaga,on
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Manual propaga+on
func foo() -> Foo? {
...
guard let value = Int(string) else {
return nil // manual
}
...
}
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Manual propaga+on
func foo() -> Result {
...
switch result {
case .success(let value):
...
case .failure(let error):
return .failure(error) // manual
}
...
}
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Automa'c propaga'on
func foo() throws -> Foo {
...
let value = try bar()
...
}
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Automa'c propaga'on
func foo(x: Int, y: Int) throws -> Int {
let a = try bar(x)
let b = try baz(y)
return a + b
}
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Manual propaga+on
func foo(x: Int, y: Int) -> Result {
bar(x).flatMap { a in
baz(y).map { b in
a + b
}
}
}
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ؔܕϓϩάϥϛϯάͷख๏͕͋Ε
Automa'c propaga'onཁΒͳ͍ʁ
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HaskellͰ͢Β do ه๏Λఏڙ͍ͯ͠Δ
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do ه๏
foo :: Int -> Int -> Either FooError Int
foo x y = do
a <- bar x
b <- baz y
return (a + b)
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do ه๏͕ͳ͍ͷʹؔܕͷख๏Ͱ͕ΜΔͱ
ίʔυͷϊΠζ͕૿͑Δ
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Swi$ͷΤϥʔϋϯυϦϯά
Kind \ Propaga-on Manual Automa-c
Simple domain Optional -
Recoverable Result throws
Universal - Ϋϥογϡ
Logic - Ϋϥογϡ
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ΤϥʔͷݪҼόά
ʢίʔυΛमਖ਼͖͢ʣ
ΤϥʔͷݪҼ͕໌֬ͰҰ͚ͭͩ
ʢݪҼผʹذ͕ඞཁͳ͍ʣ
ΤϥʔͷܕΛࢦఆ͍ͨ͠
※ ຊʹඞཁ͔ཁݕ౼
Logic failure
precondition
Simple domain error
Optional
ΤϥʔͷܕΛݶఆͯ͠ྑ͍݅Λ
ຬͨ͢
ΤϥʔΛมͰѻ͏ඞཁ͕͋Δ
※ ຊʹඞཁ͔ཁݕ౼
ΤϥʔΛมͰѻ͏ඞཁ͕͋Δ
※ ຊʹඞཁ͔ཁݕ౼
Recoverable / Automatic / Typed
throws(FooError)
Recoverable / Manual / Typed
Result
Recoverable / Manual / Untyped
Result
Recoverable / Automatic / Untyped
throws
YES
NO
ΤϥʔͷܕΛݶఆͯ͠ྑ͍݅
• Ϟδϡʔϧύοέʔδͷதʹดͯ͡Τϥʔ
ϋϯυϦϯά͢ΔΑ͏ͳ߹
• map ͷ rethrows Result ͷΑ͏ʹͦΕ
ࣗମ͕ΤϥʔΛੜΈग़͞ͳ͍߹
• Existential͕͑ͳ͍ʗΦʔόʔϔου͕ڐ༰
Ͱ͖ͳ͍߹
Slide 93
Slide 93 text
·ͱΊ
• Typed throwsΤϥʔͷܕΛࢦఆͰ͖ͯศར
• ͚Ͳɺ͍Ͳ͜ΖݶΒΕ͍ͯΔ
• throws Recoverable error
• ΤϥʔͷछྨΛҙ͍͚ࣝͯ͠Δ