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۩ମྫͱΫΠζͰֶͿɺ
Swi$ͷ4छྨͷΤϥʔͷ͍͚
Yuta Koshizawa @koher
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Q. Swi' ͰΤϥʔΛදͦ͏ͱࢥͬͨ
ͱ͖ʹԿΛ͍·͔͢ʁ
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throw FooError()
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let number: Int? =
Int(string)
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let foo: Foo? = try? foo()
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fatalError()
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assert(...)
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precondition(...)
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assertionFailure()
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preconditionFailure()
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fooOrNil!
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array[-1]
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Int.max + 1
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[Int](repeating: 42,
count: Int.max)
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func foo() { foo() }
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throw FooError()
let number: Int? = Int(String)
let foo: Foo? = try? foo()
fatalError()
assert(...)
assertionFailure()
precondition(...)
preconditionFailure()
fooOrNil!
array[-1]
Int.max + 1
[Int](repeating: 42, count: Int.max)
func foo() { foo() }
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Javaͷ߹
Throwable -+- Exception -+- RuntimeException -+- NullPointerException
| | +- IndexOutOfBoundsException
| | ...
| |
| +- IOException
| +- SQLException
| ...
|
+- Error - ... -+- OutOfMemoryError
+- StackOverflowError
...
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throw FooError()
let number: Int? = Int(string)
let foo: Foo? = try? foo()
fatalError()
assert(...)
assertionFailure()
precondition(...)
preconditionFailure()
fooOrNil!
array[-1]
Int.max + 1
[Int](repeating: 42, count: Int.max)
func foo() { foo() }
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Simple domain errors
Recoverable errors
Universal errors
Logic failures
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Simple domain errors
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let number: Int? =
Int(string)
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Simple domain errors
• ΦϖϨʔγϣϯ͕ࣦഊ͢Δલఏ͕݅໌֬
• ޭ͔ࣦͨ͠ഊ͔͕͔ͨ͠Εे
• Swi% Ͱ Optional Λฦ͢͜ͱͰද͢
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let element: Int? =
array.first
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let value =
dictionary["unknownKey"]
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Recoverable errors
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try fileManager
.removeItem(at: url)
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Recoverable errors
• ༷ʑͳݪҼͰΦϖϨʔγϣϯ͕ࣦഊ͢Δ
• ࣦഊͷݪҼΛΓ͍ͨ
• ݪҼผʹϋϯυϦϯά͍ͨ͠
• Swi% Ͱ Error Λ throw ͢Δ͜ͱͰද͢
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ճ෮ՄೳͳΤϥʔ
Simple domain errors
Recoverable errors
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ճ෮ෆೳͳΤϥʔ
Universal errors
Logic failures
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Universal errors
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[Int](repeating: 42,
count: Int.max)
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Universal error ͕ϋϯυϦϯάՄೳͩͬͨͱ͢Δͱ
// ϝϞϦෆͷϋϯυϦϯάͷྫ
let foo: Foo? = allocate(size(of: Foo))
guard let foo = foo else {
// ΤϥʔϝοηʔδͷੜͰ͞ΒʹϝϞϦෆ͕ى͜Δ͔
showAlert("ϝϞϦ͕Γ·ͤΜɻ")
}
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func foo() { foo() }
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Ctrl + C
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thread.cancel()
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Universal errors
• ίʔυதͷࢸΔͱ͜ΖͰൃੜ͢Δͷ͕ଟ͍
• ϋϯυϦϯά͠Α͏͕ͳ͍
• ίʔυ͔Βൃੜͤ͞Δʹ NSException ʢ·ͨ
fatalError ʣ
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Logic failures
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fooOrNil!
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Int.max + 1
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array[-1]
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Array ͷ subscript ͷࣦഊ͕ Logic failure ͳཧ༝
// [Int] Λιʔτ͢Δؔ
func sort(_ ns: inout [Int]) {
for i in 0 ..< ns.count {
for j in i + 1 ..< ns.count {
if ns[j] < ns[i] {
let t = ns[j]
ns[j] = ns[i]
ns[i] = t
}
}
}
}
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Array ͷ subscript ͷࣦഊ͕ Logic failure ͳཧ༝
// [Int] Λιʔτ͢Δؔ
func sort(_ ns: inout [Int]) {
for i in 0 ..< ns.count {
for j in i + 1 ..< ns.count {
if ns[j] < ns[i] {
let t = ns[j]
ns[j] = ns[i]
ns[i] = t
}
}
}
}
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Array ͷ subscript ͷࣦഊ͕ Logic failure ͳཧ༝
// ..< Λ ... ʹͯ͠͠·͏ͱΠϯσοΫε͕Έग़ͯΤϥʔ
func sort(_ ns: inout [Int]) {
for i in 0 ... ns.count {
for j in i + 1 ... ns.count {
if ns[j] < ns[i] {
let t = ns[j]
ns[j] = ns[i]
ns[i] = t
}
}
}
}
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Array ͷ subscript ͷࣦഊ͕ Logic failure ͳཧ༝
// Ͱɺ͜͜Ͱ nil ͕ฦ͖ͬͯͯϋϯυϦϯά͠Α͏͕ͳ͍
func sort(_ ns: inout [Int]) {
for i in 0 ... ns.count {
for j in i + 1 ... ns.count {
if ns[j] < ns[i] {
let t = ns[j]
ns[j] = ns[i]
ns[i] = t
}
}
}
}
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Array ͷ subscript ͷࣦഊ͕ Logic failure ͳཧ༝
// Ͳ͏ͤ ! ͢Δ͜ͱʹͳͬͯແବ
func sort(_ ns: inout [Int]) {
for i in 0 ... ns.count {
for j in i + 1 ... ns.count {
if ns[j]! < ns[i]! {
let t = ns[j]!
ns[j] = ns[i]!
ns[i] = t
}
}
}
}
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Logic failures
• ίʔυͷϛεʹΑͬͯൃੜ
• ࣮ߦ࣌Ͱͳ͘ίʔυͷमਖ਼ʹΑͬͯରԠ
• precondition, assert ͳͲͰൃੜͤ͞Δ
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ؔ -Onone -O -Ounchecked
fatalError ○ ○ ○
precondi/on ○ ○
assert ○
※ ○͕͍͍ͯͳ͍Έ߹ΘͤνΣοΫ͕লུ͞ΕΔ
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precondition ͩͱ͏Ε͍͠ཧ༝
// [Int] Λιʔτ͢Δؔ
func sort(_ ns: inout [Int]) {
for i in 0 ..< ns.count {
for j in i + 1 ..< ns.count {
if ns[j] < ns[i] {
let t = ns[j]
ns[j] = ns[i]
ns[i] = t
}
}
}
}
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precondition ͩͱ͏Ε͍͠ཧ༝
// [Int] Λιʔτ͢Δؔ
func sort(_ ns: inout [Int]) {
for i in 0 ..< ns.count {
for j in i + 1 ..< ns.count {
if ns[j] < ns[i] {
let t = ns[j]
ns[j] = ns[i]
ns[i] = t
}
}
}
}
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precondition ͩͱ͏Ε͍͠ཧ༝
// guard ͱ fatalError ͰΠϯσοΫεͷνΣοΫ
struct Array {
subscript(index: Int): Element {
get {
guard 0 <= index && index < count else {
fatalError()
}
...
}
set { ... }
}
}
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precondition ͩͱ͏Ε͍͠ཧ༝
// guard ͱ fatalError ͰΠϯσοΫεͷνΣοΫ
struct Array {
subscript(index: Int): Element {
get {
guard 0 <= index && index < count else {
fatalError()
}
...
}
set { ... }
}
}
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precondition ͩͱ͏Ε͍͠ཧ༝
// precondition -Ounchecked ͰऔΓআ͔ΕΔ
struct Array {
subscript(index: Int): Element {
get {
precondition(0 <= index && index < count)
...
}
set { ... }
}
}
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-Onone ͷͱ͖ͷڍಈ
// arrayindex.swift
let a = [2, 3, 5]
print(a[3])
$ swift arrayindex.swift
fatal error: Index out of range
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-Ounchecked ͷͱ͖ͷڍಈ
// arrayindex.swift
let a = [2, 3, 5]
print(a[3])
$ swift -Ounchecked arrayindex.swift
2392130230941712
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-Ounchecked ͷͱ͖ͷڍಈ
let a: Int? = nil
print(a!) // ࣮ߦ࣌ΤϥʔʹͳΒͳ͍
let b: UInt8 = 255
print(b + 1) // ࣮ߦ࣌ΤϥʔʹͳΒͳ͍
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Logic failure ίʔυͷϛεͷΑͬ
ͯҾ͖ى͜͞ΕΔ
↕
ίʔυͷϛε͕ͳ͚Ε Logic
failure ى͜Βͳ͍
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assert ͷ༻ྫ
assert ෦తͳ߹ੑͷνΣοΫʹ͏
import TensorSwift
// 10000 ਓͷ྆खͷࢦͷ͞
let tensor = Tensor(shape: [10000, 2, 5], elements: ...)
// [ਓ, ࠨӈ, ࢦ] ͔Β [ࢦ, ਓ, ࠨӈ] ʹม
let transposed = tensor.transposed([2, 0, 1])
// ࠨखͷσʔλ͚ͩΛऔΓग़͢
let lefthand = tensor[..., ..., 1]
// [ࢦ, ਓ] ͷॱʹͳ͍ͬͯͯ΄͍͚͠Ͳॲཧ͕ෳࡶͰࣗ৴͕࣋ͯͳ͍ͷͰνΣοΫ
assert(lefthand.shape == [5, 10000])
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Simple domain errors
Recoverable errors
Universal errors
Logic failures
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ΤϥʔͷछྨͷܾΊํ
ͲΜͳ༰ͷΤϥʔ͔
ͲͷΑ͏ʹΤϥʔϋϯυϦϯά͍͔ͤͨ͞
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// Simple domain error Ͱͳ͘ Recoverable Ͱ͋ͬͯ΄͍͠
let string = "99999999999999999999999999"
...
do {
let number: Int = try Int(string)
} catch is OverflowError {
showAlert("\(Int.min) - \(Int.max) ͷΛೖྗͯ͠Լ͍͞ɻ")
} catch {
showAlert("Λೖྗͯ͠Լ͍͞ɻ")
}
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// Universal error Ͱͳ͘ Simple domain error Ͱ͋ͬͯ΄͍͠
guard let a = malloc(MemoryLayout.size * 100_000_000) else {
showAlert("ϝϞϦ͕Γ·ͤΜɻ")
return
}
// a Λ͏ॲཧ
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// Simple domain error → Logic failure
let number: Int = Int(string)!
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from \ to SDE RE UE LF
SDE - guard let
throw
guard let
fatalError
!
RE try? - do-catch
fatalError
try!
UE -
LF if/guard
return nil
if/guard
throw
if/guard
fatalError
-
SDE: Simple domain error, RE: Recoverable error,
UE: Universal error, LF: Logic failure
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// Ͳ͏ͤ ! ͢Δ͜ͱʹͳͬͯແବ
func sort(_ ns: inout [Int]) {
for i in 0 ... ns.count {
for j in i + 1 ... ns.count {
if ns[j]! < ns[i]! {
let t = ns[j]!
ns[j] = ns[i]!
ns[i] = t
}
}
}
}
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ΫΠζλΠϜ
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ΫΠζͷϧʔϧ
- ࡾܗࣜ
- ੍ݶ࣌ؒ 30 ඵ
- શ෦Ͱ 5
- ඞͣࡾͷͲΕ͔ʹखΛڍ͛Δ
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ΫΠζͷϧʔϧ
- ࡾܗࣜ
- ੍ݶ࣌ؒ 30 ඵ
- શ෦Ͱ 5
- ඞͣࡾͷͲΕ͔ʹखΛڍ͛Δ
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ΫΠζͷϧʔϧ
- ࡾܗࣜ
- ੍ݶ࣌ؒ 30 ඵ
- શ෦Ͱ 5
- ඞͣࡾͷͲΕ͔ʹखΛڍ͛Δ
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ΫΠζͷϧʔϧ
- ࡾܗࣜ
- ੍ݶ࣌ؒ 30 ඵ
- શ෦Ͱ 5
- ඞͣࡾͷͲΕ͔ʹखΛڍ͛Δ
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@koher
h"ps:/
/twi"er.com/koher
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Q1. ϦόʔγͷϘʔυ
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let disk: Disk?
= board[x, y]
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1. Simple domain error
struct Board {
subscript(x: Int, y: Int) -> Disk? {
guard (0..<8).contains(x) else { return nil }
guard (0..<8).contains(y) else { return nil }
...
}
...
}
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2. Universal error
struct Board {
subscript(x: Int, y: Int) -> Disk? {
guard (0..<8).contains(x) else { fatalError() }
guard (0..<8).contains(y) else { fatalError() }
...
}
...
}
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3. Logic failure
struct Board {
subscript(x: Int, y: Int) -> Disk? {
precondition((0..<8).contains(x))
precondition((0..<8).contains(y))
...
}
...
}
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γϯΩϯάλΠϜ
1. Simple domain error
2. Universal error
3. Logic failure
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͑
1. Simple domain error
2. Universal error
3. Logic failure
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| ○○○●|
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| ●○○○●|
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| ○○○ |
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| ●○○○ |
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| ○○○|
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| ●○○○|
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struct Board {
subscript(x: Int, y: Int) -> Disk? {
guard (0..<8).contains(x) else { return nil }
guard (0..<8).contains(y) else { return nil }
...
}
...
}
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struct Board {
subscript(x: Int, y: Int) -> Disk? {
precondition((0..<8).contains(x))
precondition((0..<8).contains(y))
...
}
...
}
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Q2. ΞϓϦʹόϯυϧ͞Εͨσʔλ
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let foo: Foo = loadFoo()
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1. Recoverable error
func loadFoo() throws -> Foo {
guard let path = Bundle.main.path(forResource: "Foo", ofType: "json") else {
throw ...
}
let url = URL(fileURLWithPath: path)
let data = try Data(contentsOf: url)
return try JSONDecoder().decode(Foo.self, from: data)
}
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2. Universal error
func loadFoo() -> Foo {
guard let path = Bundle.main.path(forResource: "Foo", ofType: "json") else {
fatalError()
}
let url = URL(fileURLWithPath: path)
do {
let data = try Data(contentsOf: url)
return try JSONDecoder().decode(Foo.self, from: data)
} catch {
fatalError()
}
}
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3. Logic failure
func loadFoo() -> Foo {
let path = Bundle.main.path(forResource: "Foo", ofType: "json")!
let url = URL(fileURLWithPath: path)
let data = try! Data(contentsOf: url)
return try! JSONDecoder().decode(Foo.self, from: data)
}
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γϯΩϯάλΠϜ
1. Recoverable error
2. Universal error
3. Logic failure
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͑
1. Recoverable error
2. Universal error
3. Logic failure
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guard let image = UIImage(named: "Foo") else {
// ΤϥʔϋϯυϦϯά
...
}
// image Λ͏ॲཧ
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let image = UIImage(named: "Foo")!
// image Λ͏ॲཧ
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Q3. ηϯαʔ͔Βͷσʔλऔಘ
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let foo: Foo = readFoo()
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1. Recoverable error
func readFoo() throws -> Foo {
guard isFooSensorAvailable() else {
throw ...
}
...
}
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2. Universal error
func readFoo() -> Foo {
guard isFooSensorAvailable() else {
fatalError()
}
...
}
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3. Logic failure
func readFoo() -> Foo {
precondition(isFooSensorAvailable())
...
}
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γϯΩϯάλΠϜ
1. Recoverable error
2. Universal error
3. Logic failure
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͑
1. Recoverable error
2. Universal error
3. Logic failure
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Q4. ήʔϜͷηʔϒσʔλ
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let game: Game? =
loadGame()
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1. Recoverable error
func loadGame() throws -> Game? {
...
guard hash == savedHash else {
throw ...
}
...
}
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2. Universal error
func loadGame() -> Game? {
...
guard hash == savedHash else {
fatalError()
}
...
}
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3. Logic failure
func loadGame() -> Game? {
...
precondition(hash == savedHash)
...
}
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γϯΩϯάλΠϜ
1. Recoverable error
2. Universal error
3. Logic failure
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͑
1. Recoverable error
2. Universal error
3. Logic failure
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͑
1. Recoverable error
2. Universal error
3. Logic failure
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// ϥΠϒϥϦϨΠϠʔ
func loadGame() -> Game? {
...
}
// ΞϓϦϨΠϠʔ
func ... {
guard let game = loadGame() else {
fatalError()
}
// game Λ͏ίʔυ
}
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Q5. ը૾ͷੜ
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let image = Image(
width: width,
height: height,
pixels: pixels)
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1. Simple domain error
struct Image {
init?(width: Int, height: Int, pixels: [Pixel]) {
guard width >= 0 else { return nil }
guard height >= 0 else { return nil }
guard pixels.count == width * height else { return nil }
...
}
}
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2. Universal error
struct Image {
init(width: Int, height: Int, pixels: [Pixel]) {
guard width >= 0 else { return fatalError() }
guard height >= 0 else { return fatalError() }
guard pixels.count == width * height else { return fatalError() }
...
}
}
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3. Logic failure
struct Image {
init(width: Int, height: Int, pixels: [Pixel]) {
precondition(width >= 0)
precondition(height >= 0)
precondition(pixels.count == width)
...
}
}
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γϯΩϯάλΠϜ
1. Simple domain error
2. Universal error
3. Logic failure
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͑
1. Simple domain error
2. Universal error
3. Logic failure
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͑
1. Simple domain error
2. Universal error
3. Logic failure
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let a = [2, 3, 5]
a.prefix(-1) // Logic failure
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print(3...2) // Logic failure