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kishikawa katsumi / @[email protected]
Swift Expression Macros:
a practical introduction
-࣮ફ SwiftϚΫϩೖ-
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Agenda
• Macro proposal timeline
• Swift macro overview
• How to implement macros
• Swift macro essentials
• Pros and cons
• Various kinds of macros
• Declaration macros
• Practical Example: Power Assert
• Summary
࣍
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Macro proposal timeline
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• A Possible Vision for Macros in Swift
https://forums.swift.org/t/a-possible-vision-for-macros-in-swift/60900
https://gist.github.com/DougGregor/4f3ba5f4eadac474ae62eae836328b71
• Swift project in 2023
https://www.swift.org/blog/focus-areas-2023/
Macro proposal timeline
A Possible Vision for Macros in Swift
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• A Possible Vision for Macros in Swift
https://forums.swift.org/t/a-possible-vision-for-macros-in-swift/60900
• Swift project in 2023
https://www.swift.org/blog/focus-areas-2023/
➡[Pitch] Expression macros
https://forums.swift.org/t/pitch-expression-macros/61499
• [Pitch #2] Expression macros
https://forums.swift.org/t/pitch-2-expression-macros/61861
• SE-0382: Expression Macros
https://forums.swift.org/t/se-0382-expression-macros/62090
ϚΫϩʢExpression Macros/ࣜϚΫϩʣͷػೳ͕ঝೝ͞ΕΔ·Ͱ
Macro proposal timeline
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• A Possible Vision for Macros in Swift
https://forums.swift.org/t/a-possible-vision-for-macros-in-swift/60900
• Swift project in 2023
https://www.swift.org/blog/focus-areas-2023/
• [Pitch] Expression macros
https://forums.swift.org/t/pitch-expression-macros/61499
➡[Pitch #2] Expression macros
https://forums.swift.org/t/pitch-2-expression-macros/61861
• SE-0382: Expression Macros
https://forums.swift.org/t/se-0382-expression-macros/62090
ϚΫϩʢExpression Macros/ࣜϚΫϩʣͷػೳ͕ঝೝ͞ΕΔ·Ͱ
Macro proposal timeline
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• A Possible Vision for Macros in Swift
https://forums.swift.org/t/a-possible-vision-for-macros-in-swift/60900
• Swift project in 2023
https://www.swift.org/blog/focus-areas-2023/
• [Pitch] Expression macros
https://forums.swift.org/t/pitch-expression-macros/61499
• [Pitch #2] Expression macros
https://forums.swift.org/t/pitch-2-expression-macros/61861
➡SE-0382: Expression Macros
https://forums.swift.org/t/se-0382-expression-macros/62090
ϚΫϩʢExpression Macros/ࣜϚΫϩʣͷػೳ͕ঝೝ͞ΕΔ·Ͱ
Macro proposal timeline
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એݴϚΫϩʢDeclaration Macrosʣ
• [Pitch] Declaration macros
https://forums.swift.org/t/pitch-declaration-macros/62373/17
• Declaration Macros
https://github.com/DougGregor/swift-evolution/blob/declaration-macros/proposals/nnnn-declaration-macros.md
Macro proposal timeline
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Swift macro overview
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Swift Macro Overview
SwiftϚΫϩͷ֓ཁ
func f(a: Int, _: Double, c: Int) {
print(#function)
}
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func f(a: Int, _: Double, c: Int) {
print(#function) // => f(a:_:c:)
}
Swift Macro Overview
SwiftϚΫϩͷ֓ཁ
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func f(a: Int, _: Double, c: Int) {
print(#function) // => f(a:_:c:)
}
Swift Macro Overview
SwiftϚΫϩͷ֓ཁ
func f(a: Int, _: Double, c: Int) {
print("f(a:_:c:)")
}
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Swift Macro Overview
SwiftϚΫϩͷ֓ཁ
let color = #colorLiteral(red: 0.5, green: 0.5, blue: 0.25, alpha: 1.0)
let color = .init(_colorLiteralRed: 0.5, green: 0.5, blue: 0.25, alpha: 1.0)
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func doSomething(_ a: Int, b: Int, c d: Int, e _: Int, _: Int, _ _: Int) {
#printArguments()
...
}
Swift Macro Overview
SwiftϚΫϩͷ֓ཁ
https://forums.swift.org/t/se-0382-expression-macros/62090/9
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func doSomething(_ a: Int, b: Int, c d: Int, e _: Int, _: Int, _ _: Int) {
#printArguments() // => doSomething(42, b: 256, c: 512, e: _, _, _)
...
}
Swift Macro Overview
SwiftϚΫϩͷ֓ཁ
https://forums.swift.org/t/se-0382-expression-macros/62090/9
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Swift Macro Overview
SwiftϚΫϩͷ֓ཁ
func doSomething(_ a: Int, b: Int, c d: Int, e _: Int, _: Int, _ _: Int) {
print("doSomething(\(a), b: \(b), c: \(d), e: _, _, _)")
...
}
https://forums.swift.org/t/se-0382-expression-macros/62090/9
func doSomething(_ a: Int, b: Int, c d: Int, e _: Int, _: Int, _ _: Int) {
#printArguments() // => doSomething(42, b: 256, c: 512, e: _, _, _)
...
}
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Swift Macro Overview
SwiftϚΫϩͷ֓ཁ
#function "f(a:_:c:)"
#colorLiteral(
red: 0.5,
green: 0.5,
blue: 0.25,
alpha: 1.0
)
.init(
_colorLiteralRed: 0.5,
green: 0.5,
blue: 0.25,
alpha: 1.0
)
#printArguments() print("doSomething(\(a), b: \(b), c: \(d), e: _, _, _)”)
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First impressions about macros
Pros and cons
• The code might be harder to read
• Macros are hard to imagine what they do
• Incorrect conversions cause unintended behavior
• Macros are hard to debug
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First impressions about macros
Pros and cons
• The code might be harder to read
• Macros are hard to imagine what they do
• Incorrect conversions cause unintended behavior
• Macros are hard to debug
• Macro can eliminate boilerplate
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How to implement macros
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How to implement macros
#colorLiteral()
let color = #colorLiteral(red: 0.5, green: 0.5, blue: 0.25, alpha: 1.0)
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How to implement macros
#colorLiteral()
@expression public macro
colorLiteral(
red: Float, green: Float, blue: Float, alpha: Float
) -> _ColorLiteralType
= #externalMacro(module: "MacroExamplesPlugin", type: "ColorLiteralMacro")
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How to implement macros
#colorLiteral()
@expression public macro
colorLiteral(
red: Float, green: Float, blue: Float, alpha: Float
) -> _ColorLiteralType
= #externalMacro(module: "MacroExamplesPlugin", type: "ColorLiteralMacro")
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How to implement macros
#colorLiteral()
@expression public macro
colorLiteral(
red: Float, green: Float, blue: Float, alpha: Float
) -> _ColorLiteralType
= #externalMacro(module: "MacroExamplesPlugin", type: "ColorLiteralMacro")
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How to implement macros
#colorLiteral()
@expression public macro
colorLiteral(
red: Float, green: Float, blue: Float, alpha: Float
) -> _ColorLiteralType
= #externalMacro(module: "MacroExamplesPlugin", type: "ColorLiteralMacro")
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How to implement macros
#colorLiteral()
import SwiftSyntax
import _SwiftSyntaxMacros
public struct ColorLiteralMacro: ExpressionMacro {
public static func expansion(
of macro: MacroExpansionExprSyntax,
in context: inout MacroExpansionContext
) -> ExprSyntax {
let argList = replaceFirstLabel(
of: macro.argumentList,
with: "_colorLiteralRed"
)
let initSyntax: ExprSyntax = ".init(\(argList))"
if let leadingTrivia = macro.leadingTrivia {
return initSyntax.withLeadingTrivia(leadingTrivia)
}
return initSyntax
}
}
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How to implement macros
#colorLiteral()
import SwiftSyntax
import _SwiftSyntaxMacros
public struct ColorLiteralMacro: ExpressionMacro {
public static func expansion(
of macro: MacroExpansionExprSyntax,
in context: inout MacroExpansionContext
) -> ExprSyntax {
let argList = replaceFirstLabel(
of: macro.argumentList,
with: "_colorLiteralRed"
)
let initSyntax: ExprSyntax = ".init(\(argList))"
if let leadingTrivia = macro.leadingTrivia {
return initSyntax.withLeadingTrivia(leadingTrivia)
}
return initSyntax
}
}
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How to implement macros
#colorLiteral()
import SwiftSyntax
import _SwiftSyntaxMacros
public struct ColorLiteralMacro: ExpressionMacro {
public static func expansion(
of macro: MacroExpansionExprSyntax,
in context: inout MacroExpansionContext
) -> ExprSyntax {
let argList = replaceFirstLabel(
of: macro.argumentList,
with: "_colorLiteralRed"
)
let initSyntax: ExprSyntax = ".init(\(argList))"
if let leadingTrivia = macro.leadingTrivia {
return initSyntax.withLeadingTrivia(leadingTrivia)
}
return initSyntax
}
}
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How to implement macros
#colorLiteral()
import SwiftSyntax
import _SwiftSyntaxMacros
public struct ColorLiteralMacro: ExpressionMacro {
public static func expansion(
of macro: MacroExpansionExprSyntax,
in context: inout MacroExpansionContext
) -> ExprSyntax {
let argList = replaceFirstLabel(
of: macro.argumentList,
with: "_colorLiteralRed"
)
let initSyntax: ExprSyntax = ".init(\(argList))"
if let leadingTrivia = macro.leadingTrivia {
return initSyntax.withLeadingTrivia(leadingTrivia)
}
return initSyntax
}
}
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How to implement macros
#colorLiteral()
import SwiftSyntax
import _SwiftSyntaxMacros
public struct ColorLiteralMacro: ExpressionMacro {
public static func expansion(
of macro: MacroExpansionExprSyntax,
in context: inout MacroExpansionContext
) -> ExprSyntax {
let argList = replaceFirstLabel(
of: macro.argumentList,
with: "_colorLiteralRed"
)
let initSyntax: ExprSyntax = ".init(\(argList))"
if let leadingTrivia = macro.leadingTrivia {
return initSyntax.withLeadingTrivia(leadingTrivia)
}
return initSyntax
}
}
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How to implement macros
#colorLiteral()
import SwiftSyntax
import _SwiftSyntaxMacros
public struct ColorLiteralMacro: ExpressionMacro {
public static func expansion(
of macro: MacroExpansionExprSyntax,
in context: inout MacroExpansionContext
) -> ExprSyntax {
let argList = replaceFirstLabel(
of: macro.argumentList,
with: "_colorLiteralRed"
)
let initSyntax: ExprSyntax = ".init(\(argList))"
if let leadingTrivia = macro.leadingTrivia {
return initSyntax.withLeadingTrivia(leadingTrivia)
}
return initSyntax
}
}
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How to implement macros
#colorLiteral()
import SwiftSyntax
import _SwiftSyntaxMacros
public struct ColorLiteralMacro: ExpressionMacro {
public static func expansion(
of macro: MacroExpansionExprSyntax,
in context: inout MacroExpansionContext
) -> ExprSyntax {
let argList = replaceFirstLabel(
of: macro.argumentList,
with: "_colorLiteralRed"
)
let initSyntax: ExprSyntax = ".init(\(argList))"
if let leadingTrivia = macro.leadingTrivia {
return initSyntax.withLeadingTrivia(leadingTrivia)
}
return initSyntax
}
}
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Swift Syntax
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Swift Syntax
public static func expansion(
of macro: MacroExpansionExprSyntax,
in context: inout MacroExpansionContext
) -> ExprSyntax {
let argList = replaceFirstLabel(
of: macro.argumentList,
with: "_colorLiteralRed"
)
let initSyntax: ExprSyntax = ".init(\(argList))"
if let leadingTrivia = macro.leadingTrivia {
return initSyntax.withLeadingTrivia(leadingTrivia)
}
return initSyntax
}
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How to implement macros
#colorLiteral()
/// Replace the label of the
fi
rst element in the tuple with the given
/// new label.
private func replaceFirstLabel(
of tuple: TupleExprElementListSyntax,
with newLabel: String
) -> TupleExprElementListSyntax {
guard let firstElement = tuple.first else {
return tuple
}
return tuple.replacing(
childAt: 0,
with: firstElement.withLabel(.identifier(newLabel))
)
}
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How to implement macros
#colorLiteral()
/// Replace the label of the
fi
rst element in the tuple with the given
/// new label.
private func replaceFirstLabel(
of tuple: TupleExprElementListSyntax,
with newLabel: String
) -> TupleExprElementListSyntax {
guard let firstElement = tuple.first else {
return tuple
}
return tuple.replacing(
childAt: 0,
with: firstElement.withLabel(.identifier(newLabel))
)
}
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How to implement macros
#colorLiteral()
/// Replace the label of the
fi
rst element in the tuple with the given
/// new label.
private func replaceFirstLabel(
of tuple: TupleExprElementListSyntax,
with newLabel: String
) -> TupleExprElementListSyntax {
guard let firstElement = tuple.first else {
return tuple
}
return tuple.replacing(
childAt: 0,
with: firstElement.withLabel(.identifier(newLabel))
)
}
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How to implement macros
#printArguments()
func doSomething(_ a: Int, b: Int, c d: Int, e _: Int, _: Int, _ _: Int) {
#printArguments()
...
}
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How to implement macros
#printArguments()
public struct PrintArgumentsMacro: ExpressionMacro {
public static func expansion(
of node: MacroExpansionExprSyntax, in context: inout MacroExpansionContext
) -> ExprSyntax {
var syntax = node.as(Syntax.self)
while syntax != nil && syntax!.as(FunctionDeclSyntax.self) == nil {
syntax = syntax!.parent
}
guard let functionSyntax = syntax!.as(FunctionDeclSyntax.self) else { return "" }
let signature: FunctionSignatureSyntax = functionSyntax.signature
let parameterList = signature.input.parameterList
let parameters = parameterList.map { parameter -> String in
let potentialLabel = parameter.firstName!.withoutTrivia().description
let label = potentialLabel == "_" ? nil : potentialLabel
let potentialName = parameter.secondName?.withoutTrivia().description ?? potentialLabel
let name = potentialName == "_" ? nil : potentialName
var string: String
if let label {
string = "\(label): "
} else {
string = ""
}
if let name {
string += "\\(\(name))"
} else {
string += "_"
}
return string
}
let parametersString = parameters.joined(separator: ", ")
return "print(\"\(raw: functionSyntax.identifier.description)(\(raw: parametersString))\")"
}
}
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How to implement macros
#printArguments()
public struct PrintArgumentsMacro: ExpressionMacro {
public static func expansion(
of node: MacroExpansionExprSyntax, in context: inout MacroExpansionContext
) -> ExprSyntax {
var syntax = node.as(Syntax.self)
while syntax != nil && syntax!.as(FunctionDeclSyntax.self) == nil {
syntax = syntax!.parent
}
guard let functionSyntax = syntax!.as(FunctionDeclSyntax.self) else { return "" }
let signature: FunctionSignatureSyntax = functionSyntax.signature
let parameterList = signature.input.parameterList
...
}
}
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How to implement macros
#printArguments()
public struct PrintArgumentsMacro: ExpressionMacro {
public static func expansion(
of node: MacroExpansionExprSyntax, in context: inout MacroExpansionContext
) -> ExprSyntax {
var syntax = node.as(Syntax.self)
while syntax != nil && syntax!.as(FunctionDeclSyntax.self) == nil {
syntax = syntax!.parent
}
guard let functionSyntax = syntax!.as(FunctionDeclSyntax.self) else { return "" }
let signature: FunctionSignatureSyntax = functionSyntax.signature
let parameterList = signature.input.parameterList
...
}
}
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How to implement macros
#printArguments()
public struct PrintArgumentsMacro: ExpressionMacro {
public static func expansion(
of node: MacroExpansionExprSyntax, in context: inout MacroExpansionContext
) -> ExprSyntax {
var syntax = node.as(Syntax.self)
while syntax != nil && syntax!.as(FunctionDeclSyntax.self) == nil {
syntax = syntax!.parent
}
guard let functionSyntax = syntax!.as(FunctionDeclSyntax.self) else { return "" }
let signature: FunctionSignatureSyntax = functionSyntax.signature
let parameterList = signature.input.parameterList
...
}
}
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public struct PrintArgumentsMacro: ExpressionMacro {
public static func expansion(
of node: MacroExpansionExprSyntax, in context: inout MacroExpansionContext
) -> ExprSyntax {
...
let parameters = parameterList.map { parameter -> String in
let potentialLabel = parameter.firstName!.withoutTrivia().description
let label = potentialLabel == "_" ? nil : potentialLabel
let potentialName = parameter.secondName?.withoutTrivia().description ?? potentialLabel
let name = potentialName == "_" ? nil : potentialName
var string: String
if let label {
string = "\(label): "
} else {
string = ""
}
if let name {
string += "\\(\(name))"
} else {
string += "_"
}
return string
}
let parametersString = parameters.joined(separator: ", ")
return "print(\"\(raw: functionSyntax.identifier.description)(\(raw: parametersString))\")"
}
}
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Swift macro essentials
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Swift macro essentials
• Type safe
• Syntactic transformations
• Run at build time
• Additional checks at build time
• Sandboxed
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Swift macro essentials
• Type safe
• Syntactic transformations
• Run at build time
• Additional checks at build time
• Sandboxed
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Swift macro essentials
if let leadingTrivia = macro.leadingTrivia {
return initSyntax.withLeadingTrivia(leadingTrivia)
}
return initSyntax
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Swift macro essentials
• Type safe
• Syntactic transformations
• Run at build time
• Additional checks at build time
• Sandboxed
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Additional checks at build time
let homepage = #url("https://tryswift.jp/")
@expression public macro url(_ string: String) -> URL = ...
@expression public macro sql(_ string: String) -> SQLQuery = ...
let query = #sql("SELECT * FROM ...")
More ideas
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#URL()
Compile error if argument is an invalid URL
public static func expansion(
of macro: MacroExpansionExprSyntax,
in context: inout MacroExpansionContext
) throws -> ExprSyntax {
...
if !validate(macro.argumentList.first) {
context.diagnose(
Diagnostic(
node: Syntax(macro),
message: SimpleDiagnosticMessage(
message: "...",
diagnosticID: MessageID(domain: "...", id: "..."),
severity: .error
)
)
)
}
...
}
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#URL()
Compile error if argument is an invalid URL
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Swift macro essentials
• Type safe
• Syntactic transformations
• Run at build time
• Additional checks at build time
• Sandboxed
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Sandboxed
Embed binaries in apps without bundles
let data = #embed("images/icon.png")
let data = Data([0x4d, 0x49, 0x54, ..., 0x65, 0x6e, 0x73])
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Sandboxed
Can I access the
fi
le system from macros?
https://forums.swift.org/t/pitch-2-expression-macros/61861/9
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Pros and cons
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Pros and cons
👍 Macros are type safe
👍 Macros can extend Swift
👍 Macros can cooperate with the build process
🤔 Shoot yourself in the foot with any language
• Macros are hard to imagine what they do
• Macros are hard to debug
• Macros or Functions / Property Wrappers / Result Builders
🤔 Requires knowledge of Swift Syntax
🤔 Things not suited for macro
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Pros and cons
Swift Syntax
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Things not suited for macro
• Use functions in preference to macros
• Use Result Builders and Property Wrappers
• Macros are code generators
Pros and cons
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Various kinds of macros
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Various kinds of macros
Declaration macros (Freestanding macros, Attached macros)
@addCompletionHandler
func fetchAvatar(_ username: String) async -> Image? { ... }
@declaration(peers: [.overloaded]) macro addCompletionHandler: Void
/// Expansion of the macro produces the following.
func fetchAvatar(_ username: String, completionHandler: @escaping (Image?) -> Void) {
Task.detached {
completionHandler(await fetchAvatar(username))
}
}
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Various kinds of macros
Declaration macros
@optionSetMembers
struct MyOptions: OptionSet {
enum Option: Int {
case a
case b
case c
}
}
// Expands to...
struct MyOptions: OptionSet {
enum Option: Int {
case a
case b
case c
}
// Synthesized code below...
var rawValue: Int = 0
static var a = MyOptions(rawValue: 1 << Option.a.rawValue)
static var b = MyOptions(rawValue: 1 << Option.b.rawValue)
static var c = MyOptions(rawValue: 1 << Option.c.rawValue)
}
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Various kinds of macros
Declaration macros
@traced(logLevel: 2)
func myFunction(a: Int, b: Int) { ... }
@declaration(body) macro traced(logLevel: Int = 0)
if shouldLog(atLevel: 2) {
log("Entering myFunction((a: \(a), b: \(b)))")
}
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Various kinds of macros
Declaration macros
• Replace code generators with a macro
@swiftCodeGen
enum Asset {
enum Images {
static let banana = ImageAsset(value: "Exotic/Banana")
static let mango = ImageAsset(value: "Exotic/Mango")
}
enum Colors {
static let primary = ColorAsset(value: "Vengo/Primary")
static let tint = ColorAsset(value: "Vengo/Tint")
}
enum Symbols {
static let exclamationMark = SymbolAsset(name: "Exclamation Mark")
static let plus = SymbolAsset(name: "Plus")
}
}
@swiftCodeGen
enum Asset {
}
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Practical Example:
Power Assert
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What is Power Assert?
let john = Person(name: "John", age: 42)
let mike = Person(name: "Mike", age: 13)
#powerAssert(mike.isTeenager && john.age < mike.age)
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What is Power Assert?
#powerAssert(mike.isTeenager && john.age < mike.age)
| | | | | | | |
| false | | 42 | | 13
| | | | Person(name: "Mike", age: 13)
| | | false
| | Person(name: "John", age: 42)
| false
Person(name: "Mike", age: 13)
let john = Person(name: "John", age: 42)
let mike = Person(name: "Mike", age: 13)
#powerAssert(mike.isTeenager && john.age < mike.age)
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Why Power Assert?
Many di
ff
erent assertion functions
public func XCTAssert()
public func XCTAssertEqual()
public func XCTAssertEqualWithAccuracy()
public func XCTAssertFalse()
public func XCTAssertGreaterThan()
public func XCTAssertGreaterThanOrEqual()
public func XCTAssertIdentical()
public func XCTAssertLessThan()
public func XCTAssertLessThanOrEqual()
public func XCTAssertNil()
public func XCTAssertNoThrow()
public func XCTAssertNotEqual()
public func XCTAssertNotEqualWithAccuracy()
public func XCTAssertNotIdentical()
public func XCTAssertNotNil()
public func XCTAssertThrowsError()
public func XCTAssertTrue()
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Why Power Assert?
Many di
ff
erent assertion functions
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Why Power Assert?
Many di
ff
erent assertion functions
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Why Power Assert?
Many di
ff
erent assertion functions
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What is Power Assert?
• Only simple assert function such as powerAssert(a == b) is su
ff
i
cient
• Display easy-to-understand information on assert failure (when the test does
not pass)
• Bene
fi
t of not having to use many di
ff
erent assertion functions
https://azu.github.io/slide/sakurajs/power-assert.html#/2
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Why Power Assert?
That's all you need
@expression
public macro powerAssert(_ expression: @autoclosure () throws -> Bool)
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Implement Power Assert with
macros
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Implement Power Assert with macros
#powerAssert(a * b == 91)
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Implement Power Assert with macros
https://swift-ast-explorer.com/
Swift AST Explorer
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Implement Power Assert with macros
#powerAssert(a * b == 91)
TupleExprElementList
Inspect the macro syntax structure
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Implement Power Assert with macros
#powerAssert(a * b == 91)
TupleExprElementList
Identi
fi
erExpr
Inspect the macro syntax structure
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Implement Power Assert with macros
#powerAssert(a * b == 91)
TupleExprElementList
Identi
fi
erExpr
BinaryOperatorExpr
Inspect the macro syntax structure
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Implement Power Assert with macros
#powerAssert(a * b == 91)
TupleExprElementList
Identi
fi
erExpr
BinaryOperatorExpr
IntegerLiteralExpr
Inspect the macro syntax structure
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Implement Power Assert with macros
PowerAssert.Assertion(#"#powerAssert(a * b == 91)"#, line: 2)
.assert(a * b == 91)
.capture(expression: a.self, column: 13)
.capture(expression: b.self, column: 17)
.capture(expression: a * b == 91, column: 19)
.capture(expression: 91, column: 22)
.render()
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Implement Power Assert with macros
PowerAssert.Assertion(#"#powerAssert(a * b == 91)"#, line: 2)
.assert(a * b == 91)
.capture(expression: a.self, column: 13)
.capture(expression: b.self, column: 17)
.capture(expression: a * b == 91, column: 19)
.capture(expression: 91, column: 22)
.render()
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Implement Power Assert with macros
PowerAssert.Assertion(#"#powerAssert(a * b == 91)"#, line: 2)
.assert(a * b == 91)
.capture(expression: a.self, column: 13)
.capture(expression: b.self, column: 17)
.capture(expression: a * b == 91, column: 19)
.capture(expression: 91, column: 22)
.render()
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Implement Power Assert with macros
PowerAssert.Assertion(#"#powerAssert(a * b == 91)"#, line: 2)
.assert(a * b == 91)
.capture(expression: a.self, column: 13)
.capture(expression: b.self, column: 17)
.capture(expression: a * b == 91, column: 19)
.capture(expression: 91, column: 22)
.render()
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Implement Power Assert with macros
PowerAssert.Assertion(#"#powerAssert(a * b == 91)"#, line: 2)
.assert(a * b == 91)
.capture(expression: a.self, column: 13)
.capture(expression: b.self, column: 17)
.capture(expression: a * b == 91, column: 19)
.capture(expression: 91, column: 22)
.render()
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Implement Power Assert with macros
PowerAssert.Assertion(#"#powerAssert(a * b == 91)"#, line: 2)
.assert(a * b == 91)
.capture(expression: a.self, column: 13)
.capture(expression: b.self, column: 17)
.capture(expression: a * b == 91, column: 19)
.capture(expression: 91, column: 22)
.render()
// => #powerAssert(a * b == 91)
| | | |
10 9 | 91
false
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Implement Power Assert with macros
PowerAssert.Assertion(#"#powerAssert(a * b == 91)"#, line: 2)
.assert(a * b == 91)
.capture(expression: a.self, column: 13)
.capture(expression: b.self, column: 17)
.capture(expression: a * b == 91, column: 19)
.capture(expression: 91, column: 22)
.render()
// => #powerAssert(a * b == 91)
| | | |
10 9 | 91
false
#powerAssert(a * b == 91)
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Implement Power Assert with macros
#powerAssert(String(data: data, encoding: .utf8) == "test")
FunctionCallExpr
Identi
fi
erExpr MemberAccessExpr
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Implement Power Assert with macros
#powerAssert(String(data: data, encoding: .utf8) == "test")
FunctionCallExpr
Identi
fi
erExpr MemberAccessExpr
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Implement Power Assert with macros
PowerAssert.Assertion(#"#powerAssert(String(data: data, encoding: .utf8) == "test")"#, line: 2)
.assert(String(data: data, encoding: .utf8) == "test")
.capture(expression: String(data: data, encoding: .utf8), column: 13)
.capture(expression: data.self, column: 26)
.capture(expression: .utf8, column: 42)
.capture(expression: String(data: data, encoding: .utf8) == "test", column: 49)
.capture(expression: "test", column: 52)
.render()
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Implement Power Assert with macros
PowerAssert.Assertion(#"#powerAssert(String(data: data, encoding: .utf8) == "test")"#, line: 2)
.assert(String(data: data, encoding: .utf8) == "test")
.capture(expression: String(data: data, encoding: .utf8), column: 13)
.capture(expression: data.self, column: 26)
.capture(expression: .utf8, column: 42)
.capture(expression: String(data: data, encoding: .utf8) == "test", column: 49)
.capture(expression: "test", column: 52)
.render()
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Implement Power Assert with macros
.capture(expression: data.self, column: 26)
.capture(expression: .utf8, column: 42)
.capture(expression: String(data: data,
No type information in syntax tree
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Implement Power Assert with macros
https://github.com/apple/swift-evolution/blob/main/proposals/0382-expression-macros.md#macro-argument-type-information
No type information in syntax tree
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Implement Power Assert with macros
https://github.com/apple/swift-evolution/blob/main/proposals/0382-expression-macros.md#macro-argument-type-information
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Implement Power Assert with macros
https://github.com/apple/swift-evolution/blob/main/proposals/0382-expression-macros.md#example-expression-macros
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https://github.com/kishikawakatsumi/swift-power-assert
Implement Power Assert with macros
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Summary
Macros are fun!
• Macros are a very powerful feature that can extend Swift itself
• Shoot yourself in the foot if used incorrectly
• Swift Syntax becomes more important
• Macros are hard to debug
• Post your ideas!
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Easy? Difficult?
https://forums.swift.org/t/pitch-declaration-macros/62373/21
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Easy? Difficult?
https://forums.swift.org/t/pitch-declaration-macros/62373/25
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Summary
Macros are fun!
• Macros are a very powerful feature that can extend Swift itself
• Shoot yourself in the foot if used incorrectly
• Swift Syntax becomes more important
• Macros are hard to debug
• Post your ideas!
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References
• A Possible Vision for Macros in Swift
https://forums.swift.org/t/a-possible-vision-for-macros-in-swift/60900
• Swift project in 2023
https://www.swift.org/blog/focus-areas-2023/
• [Pitch] Expression macros
https://forums.swift.org/t/pitch-expression-macros/61499
• [Pitch #2] Expression macros
https://forums.swift.org/t/pitch-2-expression-macros/61861
• SE-0382: Expression Macros
https://forums.swift.org/t/se-0382-expression-macros/62090
• [Pitch] Declaration macros
https://forums.swift.org/t/pitch-declaration-macros/62373/36
• 5͙Β͍ͰΘ͔Δpower assert
https://azu.github.io/slide/sakurajs/power-assert.html