try! Swift NYC 2019 Session

1. A Deeper Deep dive into Swift Literals
freddi from LINE Fukuoka
at try! Swift NYC 2019 (9th.Sep)

2. About Me
freddi (Yuki Aki) from !
Developing LINE Creators Studio
at LINE Fukuoka
Organizer of HAKATA.swift

3. - What is a Literal in Computer Programming?
- Why I want you to deep dive into Swift Literals?
- Literals in Swift
- Object of Literals
- Architecture of Type from Literals
- Conclusion
Agenda
High-Level
Low-Level

4. What is a Literal
in Computer Programming?

5. What is a Literal in Computer Programming?
What is a Literal in Computer Programming?
Notations for representing a fixed value in source code.
Values we write in a conventional form whose is obvious

6. // Integer Literal
let assigningIntegerLiteral = 42
// String Literal
let assigningStringLiteral = "try! Swift"
What is a Literal in Computer Programming?

7. Literal is a minimal way to
represent the actual data for Programmer
What is a Literal in Computer Programming?

8. Why I want you to
deep-dive into Swift Literals?

9. Why I want you to deep-dive into Swift Literals?
We have more chances to touch low level Swift
compared to Other Languages

10. Why I want you to deep-dive into Swift Literals?

11. But,it is not easy to learn 😩
Why I want you to deep-dive into Swift Literals?

12. Compiler Code looks too difficult and is too long for reading
Why I want you to deep-dive into Swift Literals?

13. Why I talk about Literals?
Why I want you to deep-dive into Swift Literals?

14. Why I talk about Literals?
I learned Swift Compiler things
through understanding deep side of Swift Literals
Why I want you to deep-dive into Swift Literals?

15. Literals in Swift

16. Literals in Swift (Basic Literals)
// Integer Literal
let assigningIntegerLiteral = 42
// Float Literal
let assigningFloatLiteral = 10.0
// String Literal
let assigningStringLiteral = "try! Swift"
// Boolean Literal
let assigningBooleanLiteral = true

17. Representing basic data
- Integer Literal → integer numeric
- Float Literal → floating numeric
- String Literal → sentence
- Boolean Literal → true/false
Literals in Swift (Basic Literals)

18. Literals in Swift (Basic Literals with nested Type)
// Optional from Nil Literal
let assigningNilLiteral: Int? = nil
// Array Literal
let assigningArrayLiteralWithInt: [Int] = [42]
// Dictionary Literal
let assigningDictLiteral: [String: Int] = [:]

19. Context of Nested Values is necessary
- Nil Literal → null value
- Array Literal → sequencial value
- Dictionary Literal → value with key
Literals in Swift (Basic Literals with nested Type)

20. Literals in Swift (Basic Literals with nested Type)
// Not declared what type you want to make optional
❌ let assigningNilLiteral = nil
// Not declared what element type
❌ let assigningArrayLiteral = []

21. Literals in Swift (Special Literals)
// Color Literal
let color = #colorLiteral(red: 1, green: 0, blue: 0, alpha: 1)
// Image Literal
let image = #imageLiteral(resourceName: “cat”)
// File Reference Literal
let file = #fileLiteral(resourceName: “cat.txt”)

22. Swift also provides Special Literals for resources
- Color Literal → color
- Image Literal → image
- File Reference Literal → file location
Literals in Swift (Special Literals)

23. Literals in Swift (Special Literals)
Color/Image/File Reference Literal are
- rendered as Actual Data in Xcode
- File → select from file manager
- Color → adjusting color code

24. // Color Literal
let color = #colorLiteral(red: 1, green: 0, blue: 0, alpha: 1)
Literals in Swift (Special Literals)

25. Literals in Swift (Special Literals at Xcode!)
// Color Literal
let color =

26. // Color Literal
let color =
Literals in Swift (Special Literals at Xcode!)

27. // Image Literal
let image = #imageLiteral(resourceName: “cat")
Literals in Swift (Special Literals)

28. // Image Literal
let image =
Literals in Swift (Special Literals at Xcode!)

29. // Image Literal
let image =
Literals in Swift (Special Literals at Xcode!)

30. Literals are a minimal way to represent value by programmer
There are many Literals in Swift,not only usual Literal!
- Integer,Array,Nil,Color etc…
Literals in Swift

31. Object of Literals

32. Object of Literals
The Ways of determining Type of value are …
- Type Annotation
- Type Inference with Default Type of Literal

33. // Integer Literal
// assigningIntegerLiteral is Int
let assigningIntegerLiteral: Int = 42
Literals get Type from annotation after colon(:)
Object of Literals(Type Annotation)

34. // Integer Literal
// assigningIntegerLiteral is Float
let assigningIntegerLiteral: Float = 42
Literals get Type from annotation after colon(:)
Object of Literals(Type Annotation)

35. Object of Literals
The Ways of determining Type of value are …
- Type Annotation
- Type Inference with Default Type of Literal

36. Object of Literals (Type Inference)
// Integer Literal
// assigningIntegerLiteral is Int
let assigningIntegerLiteral = 42
Each Literal has Default Type,can be inferenced

37. Object of Literals (Special Literals)
// Image Literal
let image = #imageLiteral(resourceName: “cat”)
type(of: image) // UIImage at UIKit, NSImage at AppKit
AppKit UIKit
Image Literal NSImage UIImage
Color Literal NSColor UIColor

38. Object of Literals
Some Literals are treated as Object
which cannot be used Directly

39. Swift’s Compiling Flow
42 SIL(Swift Intermediate Language)
Abstract Syntax Tree(AST)
AST With Type information

40. Swift’s Compiling Flow
42 SIL(Swift Intermediate Language)
Abstract Syntax Tree(AST)
AST With Type information
Front-End of Compiler
Back-End of Compiler

41. 42 SIL(Swift Intermediate Language)
Abstract Syntax Tree(AST)
AST With Type information
Swift’s Compiling Flow

42. SIL (Swift Intermediate Language)
Intermediate Language between Swift and LLVM IR
- Swift code will be converted SIL after AST
- Some of optimization are operated at SIL

43. Format of SIL
SIL is conforming Static Single Assignment format
%a = some value 1 ⭕
%b = some value 2 ⭕
%a = some value 3 ❌
Value
- Object is assigned to value at each line
- Assigning to one value is allowed only once

44. SIL (Swift Intermediate Language)
Why do we need SIL when deep dive into Literals?

45. SIL (Swift Intermediate Language)
Why do we need SIL when deep dive into Literals?
We can find how Swift Code is treated by Compiler

46. SIL (Swift Intermediate Language)
Why do we need SIL when deep dive into Literals?
We can find how Swift Code is treated by Compiler
More easy to read SIL than reading compiler code

47. Let’s read SIL
let assigningLiteral: Int = 42

48. let assigningLiteral: Int = 42
%3 = global_addr @$s4test16assigningLiteralSivp : $*Int
%4 = integer_literal $Builtin.Int64, 42
%5 = struct $Int (%4 : $Builtin.Int64)
store %5 to %3 : $*Int
Let’s read SIL

49. %3 = global_addr @$s4test16assigningLiteralSivp : $*Int
%4 = integer_literal $Builtin.Int64, 42
%5 = struct $Int (%4 : $Builtin.Int64)
store %5 to %3 : $*Int
let assigningLiteral: Int = 42
Let’s read SIL

50. let assigningLiteral: Int = 42
Allocation of memory to %3
%3 = global_addr @$s4test16assigningLiteralSivp : $*Int
%4 = integer_literal $Builtin.Int64, 42
%5 = struct $Int (%4 : $Builtin.Int64)
store %5 to %3 : $*Int
Let’s read SIL

51. $Builtin.Int64 object is assigned %4
%3 = global_addr @$s4test16assigningLiteralSivp : $*Int
%4 = integer_literal $Builtin.Int64, 42
%5 = struct $Int (%4 : $Builtin.Int64)
store %5 to %3 : $*Int
let assigningLiteral: Int = 42
Let’s read SIL

52. At first,Some Literals are …
%4 = integer_literal $Builtin.Int64, 42
Literal Object
- treated as “Literal Object” starts with $Builtin.***
- $Builtin.*** will be used in Actual Type Initializer

53. %4 = integer_literal $Builtin.Int64, 42
Literal Object
At first,Some Literals are …
- treated as “Literal Object” starts with $Builtin.***
- $Builtin.*** will be used in Actual Type Initializer
Un-official name!;(

54. 42
$Builtin.Int64
4.2
$Builtin.FPIEEE64
“42”
$Builtin.RawPointer
$Builtin.Word
Integer Float String
Literal Object

55. 42
$Builtin.Int64
4.2
$Builtin.FPIEEE64
“42”
$Builtin.RawPointer
$Builtin.Word
Integer Float String
let value: Float = 42
Literal Object

56. true
$Builtin.Int1
Boolean Digit after $Buildin.Int means bit-size
Integer
42
$Builtin.Int64
Literal Object

57. true
$Builtin.Int1
Boolean Digit after $Buildin.Int means bit-size
Integer
42
$Builtin.Int64
Literal Object

58. #imageLiteral(resourceName: “cat”)
UIImage(named: “cat”)
Image Literal(at import UIKit)
No Literal Object!
Literal Object

59. $Builtin.Int64 object is assigned %4
%3 = global_addr @$s4test16assigningLiteralSivp : $*Int
%4 = integer_literal $Builtin.Int64, 42
%5 = struct $Int (%4 : $Builtin.Int64)
store %5 to %3 : $*Int
let assigningLiteral: Int = 42
Let’s read SIL

60. let assigningLiteral: Int = 42
%3 = global_addr @$s4test16assigningLiteralSivp : $*Int
%4 = integer_literal $Builtin.Int64, 42
%5 = struct $Int (%4 : $Builtin.Int64)
store %5 to %3 : $*Int
Let’s read SIL
$Builtin.Int64 object is assigned %4

61. %3 = global_addr @$s4test16assigningLiteralSivp : $*Int
%4 = integer_literal $Builtin.Int64, 42
%5 = struct $Int (%4 : $Builtin.Int64)
store %5 to %3 : $*Int
Literal Object (%4) is passed to Int Initializer
Let’s read SIL let assigningLiteral: Int = 42

62. Some Type which can be generated from Literal
Let’s read SIL
- has initializer which receives Literal Object
- Initializer of default Type is used,if type not annotated

63. %3 = global_addr @$s4test16assigningLiteralSivp : $*Int
%4 = integer_literal $Builtin.Int64, 42
%5 = struct $Int (%4 : $Builtin.Int64)
store %5 to %3 : $*Int
Literal Object (%4) is passed to Int Initializer
Let’s read SIL let assigningLiteral: Int = 42

64. %3 = global_addr @$s4test16assigningLiteralSivp : $*Int
%4 = integer_literal $Builtin.Int64, 42
%5 = struct $Int (%4 : $Builtin.Int64)
store %5 to %3 : $*Int
The generated Int Object is assigned to allocated place
let assigningLiteral: Int = 42Let’s read SIL

65. "try! Swift"
Let’s read SIL

66. "try! Swift"
%2 = string_literal utf8 "try! Swift" // user: %7
%3 = integer_literal $Builtin.Word, 10 // user: %7
%4 = integer_literal $Builtin.Int1, -1 // user: %7
%5 = metatype $@thin String.Type // user: %7
// function_ref String.init(_builtinStringLiteral:utf8CodeUnitCount:isASCII:)
%6 = function_ref ...
%7 = apply %6(%2, %3, %4, %5) ...
Let’s read SIL(from string literal to String)

67. %2 = string_literal utf8 "try! Swift" // user: %7
%3 = integer_literal $Builtin.Word, 10 // user: %7
%4 = integer_literal $Builtin.Int1, -1 // user: %7
%5 = metatype $@thin String.Type // user: %7
// function_ref String.init(_builtinStringLiteral:utf8CodeUnitCount:isASCII:)
%6 = function_ref ...
%7 = apply %6(%2, %3, %4, %5) ...
Let’s read SIL(from string literal to String)

68. Let’s read SIL(from string literal to String)
%2 = string_literal utf8 "try! Swift" // user: %7
%3 = integer_literal $Builtin.Word, 10 // user: %7
%4 = integer_literal $Builtin.Int1, -1 // user: %7
%2: $Builtin.RawPointer // pointer of string
%4: $Builtin.Int1 // flag string is Ascii or not
%3: $Builtin.Word // length of data on memory

69. %2 = string_literal utf8 "try! Swift" // user: %7
%3 = integer_literal $Builtin.Word, 10 // user: %7
%4 = integer_literal $Builtin.Int1, -1 // user: %7
%5 = metatype $@thin String.Type // user: %7
// function_ref String.init(_builtinStringLiteral:utf8CodeUnitCount:isASCII:)
%6 = function_ref ...
%7 = apply %6(%2, %3, %4, %5) ...
Let’s read SIL(from string literal to String)

70. // function_ref String.init(_builtinStringLiteral:utf8CodeUnitCount:isASCII:)
%6 = function_ref ...
%7 = apply %6(%2, %3, %4, %5) ...
Let’s read SIL(from string literal to String)

71. Swift Literals are treated as Literal Object at first
- Literal Object will be used for Initializers of actual Swift Type
Object of Literals
%5 = struct $Int (%4 : $Builtin.Int64)

72. Architecture of Type
from Literals

73. Literal Object
At first,Some Literals are treated as “Literal Object”
42
$Builtin.Int64
4.2
$Builtin.FPIEEE64
“42”
$Builtin.RawPointer
$Builtin.Word
Integer Float String

74. %3 = global_addr @$s4test16assigningLiteralSivp : $*Int
%4 = integer_literal $Builtin.Int64, 42
%5 = struct $Int (%4 : $Builtin.Int64)
store %5 to %3 : $*Int
Literal Object is passed to Int Initializer
Initializer which receives Literal Object

75. Implementation of this initializer is required by
_ExpressibleByBuiltin***Literal protocol
%5 = struct $Int (%4 : $Builtin.Int64)
Initializer which receives Literal Object

76. What is _ExpressibleByBuiltin***Literal protocol?
_ExpressibleByBuiltin***Literal

77. What is _ExpressibleByBuiltin***Literal protocol?
_ExpressibleByBuiltin***Literal
public protocol _ExpressibleByBuiltinIntegerLiteral {
init(_builtinIntegerLiteral value: Builtin.IntLiteral)
}
init(:Builtin.IntLiteral) is called on assigning Literal by =
- Type which conforming with this protocol is convertible by Literal Object

78. _ExpressibleByBuiltin***Literal
init(:Builtin.IntLiteral) is called on assigning Literal by =
%5 = struct $Int (%4 : $Builtin.Int64)
What is _ExpressibleByBuiltin***Literal protocol?
- Type which conforming with this protocol is convertible by Literal Object

79. ExpressibleBy***Literal
You may know ExpressibleBy***Literal protocol
- makes Type be convertible by each Literal,using =
- ExpressibleByIntegerLiteral
- ExpressibleByFloatLiteral
- ExpressibleByBooleanLiteral …

80. struct OriginalIntegerType: ExpressibleByIntegerLiteral {
typealias IntegerLiteralType = Int
init(integerLiteral value: IntegerLiteralType) {}
}
let value: OriginalIntegerType = 10
ExpressibleBy***Literal
How to make Original Type convertible from Literal?

81. struct OriginalIntegerType: ExpressibleByIntegerLiteral {
typealias IntegerLiteralType = Int
init(integerLiteral value: IntegerLiteralType) {}
}
let value: OriginalIntegerType = 10
1.Set typealias to IntegerLiteralType
the type should be converted from Integer Literal
ExpressibleBy***Literal
How to make Original Type convertible from Literal?

82. struct OriginalIntegerType: ExpressibleByIntegerLiteral {
typealias IntegerLiteralType = Int
init(integerLiteral value: IntegerLiteralType) {}
}
let value: OriginalIntegerType = 10
2.Implement Initializer
which receives IntegerLiteralType value
ExpressibleBy***Literal
How to make Original Type convertible from Literal?

83. struct OriginalIntegerType: ExpressibleByIntegerLiteral {
typealias IntegerLiteralType = Int
init(integerLiteral value: IntegerLiteralType) {}
}
let value: OriginalIntegerType = 10
You can initialize your type by Literal!
ExpressibleBy***Literal
How to make Original Type convertible from Literal?

84. ExpressibleBy***Literal
public struct CGFloat {
#if arch(i386) || arch(arm)
public typealias NativeType = Float
#elseif arch(x86_64) || arch(arm64) || …
public typealias NativeType = Double
...
typealias FloatLiteralType = NativeType
CGFloat is using ExpressibleByFloatLiteral

85. struct OriginalIntegerType: ExpressibleByIntegerLiteral {
typealias IntegerLiteralType = Int
init(integerLiteral value: IntegerLiteralType) {}
}
let value: OriginalIntegerType = 10
ExpressibleBy***Literal
How to make Original Type convertible from Literal?
1.Set typealias to IntegerLiteralType
the type should be converted from Integer Literal

86. Associated Type in ExpressibleBy***Literal should conform
with _ExpressibleByBuiltin***Literal protocol
public protocol ExpressibleByIntegerLiteral {
associatedtype IntegerLiteralType: _ExpressibleByBuiltinIntegerLiteral
ExpressibleBy***Literal

87. Flow of Converting Literal
Literal Object ( = Builtin.***)
Swift Type
Literal

88. Swift Type
Literal Object ( = Builtin.***)
Swift Type: _ExpressibleByBuiltin***
Swift Type: ExpressibleBy***
Literal
Optional →
Flow of Converting Literal

89. _ExpressibleByBuiltin***Literal
Please note that …
You cannot use _ExpressibleByBuiltin***Literal protocol
in your usual Swift Code 🙃 🙃 🙃

90. $Builtin.Int64 $Builtin.FPIEEE64
What is “Literal Object” ??? 🤔
$Builtin.RawPointer
$Builtin.Word
Literal Object

91. Literal Object
Implementation of this initializer is required by
_ExpressibleByBuiltin***Literal protocol
%5 = struct $Int (%4 : $Builtin.Int64)

92. Where will passed Literal Object go?
%5 = struct $Int (%4 : $Builtin.Int64)
Literal Object

93. public struct Int : …… {
public var _value: Builtin.Int64
Literal Object will be stored in Some Swift Types from Literal
Literal Object

94. // static Int.== infix(_:_:)
sil public_external ... (Int, Int, @thin Int.Type) -> Bool {
...
%3 = struct_extract %0 : $Int, #Int._value // user: %5
%4 = struct_extract %1 : $Int, #Int._value // user: %5
%5 = builtin "cmp_eq_Int64"(%3 : $Builtin.Int64, %4 : $Builtin.Int64) ...
%6 = struct $Bool (%5 : $Builtin.Int1) // user: %7
public var _value: Builtin.Int64
== operator on Int
Literal Object

95. // static Int.== infix(_:_:)
sil public_external ... (Int, Int, @thin Int.Type) -> Bool {
...
%3 = struct_extract %0 : $Int, #Int._value // user: %5
%4 = struct_extract %1 : $Int, #Int._value // user: %5
%5 = builtin "cmp_eq_Int64"(%3 : $Builtin.Int64, %4 : $Builtin.Int64) ...
%6 = struct $Bool (%5 : $Builtin.Int1) // user: %7
public var _value: Builtin.Int64
1.Getting _value from left value and right value
Literal Object
== operator on Int

96. // static Int.== infix(_:_:)
sil public_external ... (Int, Int, @thin Int.Type) -> Bool {
...
%3 = struct_extract %0 : $Int, #Int._value // user: %5
%4 = struct_extract %1 : $Int, #Int._value // user: %5
%5 = builtin "cmp_eq_Int64"(%3 : $Builtin.Int64, %4 : $Builtin.Int64) ...
%6 = struct $Bool (%5 : $Builtin.Int1) // user: %7
public var _value: Builtin.Int64
2. Passing each _value to Back-End function
Literal Object
== operator on Int

97. Swift Type from Literal
Swift’s Compiling Flow
Front-End of Compiler
Back-End of Compiler
$Builtin.*** Back-End Object

98. // static Int.== infix(_:_:)
sil public_external ... (Int, Int, @thin Int.Type) -> Bool {
...
%3 = struct_extract %0 : $Int, #Int._value // user: %5
%4 = struct_extract %1 : $Int, #Int._value // user: %5
%5 = builtin "cmp_eq_Int64"(%3 : $Builtin.Int64, %4 : $Builtin.Int64) ...
%6 = struct $Bool (%5 : $Builtin.Int1) // user: %7
public var _value: Builtin.Int64
3.Return result as Bool in Swift
Literal Object
== operator on Int

99. Swift Type
Literal Object ( = Builtin.***)
Swift Type: _ExpressibleByBuiltin***
Swift Type: ExpressibleBy***
Literal
Flow of Converting Literal

100. Literal
Swift Type: ExpressibleBy***
Swift Type: _ExpressibleByBuiltin***
Literal Object ( = Builtin.***)
Architecture of Type from Literals
Int, String …
CGFloat …

101. Operators(+,-,*,/,== …)
Operators(+,-,*,/,== …)
Architecture of Type from Literals
Back-End Function
ift Type: ExpressibleBy***
ype: _ExpressibleByBuiltin***
eral Object ( = Builtin.***)
Swift Ty
Swift Type:
Literal O

102. Some Types generated from Literals are wrappers of Literal Object
Literal Object represents object in Back-End
Architecture of Type from Literals

103. $Builtin.Int64
Int UInt
Architecture of Type from Literals
Some Types generated from Literals are wrappers of Literal Object
Literal Object represents object in Back-End

104. Some Types generated from Literals are wrappers of Literal Object
Literal Object represents object in Back-End
Architecture of Type from Literals

105. Some Types generated from Literals are wrappers of Literal Object
Literal Object represents object in Back-End
Architecture of Type from Literals
Swift Type from Literal
$Builtin.*** Back-End Object

106. Conclusion

107. Literals in Swift
Literals are a minimal way to represent value by programmer
There are many Literals in Swift,not only usual Literal!
- Integer,Array,Nil,Color etc…

108. Literal Object
At first,Some Literals are treated as “Literal Object”
42
$Builtin.Int64
4.2
$Builtin.FPIEEE64
“42”
$Builtin.RawPointer
$Builtin.Word
Integer Float String

109. %3 = global_addr @$s4test16assigningLiteralSivp : $*Int
%4 = integer_literal $Builtin.Int64, 42
%5 = struct $Int (%4 : $Builtin.Int64)
store %5 to %3 : $*Int
Literal Object is passed to Int Initializer
Initializer which receives Literal Object

110. Architecture of Type from Literals
Literal
Swift Type: ExpressibleBy***
Swift Type: _ExpressibleByBuiltin***
Literal Object ( = Builtin.***)
Int, String …
CGFloat …

111. For more your understanding

112. https://github.com/apple/swift
For more your understanding

113. https://www.youtube.com/watch?v=sT0SNp-Tw-8
For more your understanding

114. Swiftckaigi
19th November 2019@Japan
For more your understanding

115. Thank you for listening!