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Add ChangeLog entry for macros

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Doug Gregor
2023-05-24 22:39:13 -07:00
parent db0a7287a5
commit af4831c3a5
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CHANGELOG.md
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@@ -5,6 +5,69 @@
## Swift 5.9
* [SE-0382][], [SE-0389][], [SE-0394][], [SE-0397][]:
Swift 5.9 includes a new macro system that can be used to eliminate boilerplate and provide new forms of expressive APIs. Macros are declared with the new `macro` introducer:
```swift
@freestanding(expression)
macro assert(_ condition: Bool) = #externalMacro(module: "PowerAssertMacros", type: "AssertMacro")
```
Macros have parameter and result types, like functions, but are defined as separate programs that operate on syntax trees (using [swift-syntax][]) and produce new syntax trees that are incorporated into the program. Freestanding macros, indicated with the `@freestanding` attribute, are expanded in source code with a leading `#`:
```swift
#assert(x + y == z) // expands to check the result of x + y == z and report failure if it's false
```
Macros can also be marked as `@attached`, in which case they will be meaning that they will be expanded using custom attribute syntax. For example:
```swift
@attached(peer, names: overloaded)
macro AddCompletionHandler() = #externalMacro(
module: "ConcurrencyHelperMacros",
type: "AddCompletionHandlerMacro"
)
@AddCompletionHandler
func fetchAvatar(from url: URL) throws -> Image { ... }
// expands to...
func fetchAvatar(from url: URL, completionHandler: @escaping (Result<Image, Error>) -> Void) {
Task.detached {
do {
let result = try await fetchAvatar(from: url)
completionHandler(.success(result))
} catch {
completionHandler(.failure(error))
}
}
}
```
Macros are implemented in separate programs, which are executed by the Swift compiler. The Swift Package Manager's manifest provides a new `macro` target type to describe macros:
```swift
import PackageDescription
import CompilerPluginSupport
let package = Package(
name: "ConcurrencyHelpers",
dependencies: [
.package(url: "https://github.com/apple/swift-syntax", from: "509.0.0"),
],
targets: [
.macro(name: "ConcurrencyHelperMacros",
dependencies: [
.product(name: "SwiftSyntaxMacros", package: "swift-syntax"),
.product(name: "SwiftCompilerPlugin", package: "swift-syntax")
]),
.target(name: "ConcurrencyHelpers", dependencies: ["ConcurrencyHelperMacros"]),
.testTarget(name: "ConcurrencyHelperMacroTests", dependencies: ["ConcurrencyHelperMacros"]),
]
)
```
* [SE-0380][]:
`if` and `switch` statements may now be used as expressions to:
@@ -9766,7 +9829,10 @@ using the `.dynamicType` member to retrieve the type of an expression should mig
[SE-0376]: <https://github.com/apple/swift-evolution/blob/main/proposals/0376-function-back-deployment.md>
[SE-0377]: <https://github.com/apple/swift-evolution/blob/main/proposals/0377-parameter-ownership-modifiers.md>
[SE-0380]: <https://github.com/apple/swift-evolution/blob/main/proposals/0380-if-switch-expressions.md>
[SE-0382]: https://github.com/apple/swift-evolution/blob/main/proposals/0382-expression-macros.md
[SE-0389]: https://github.com/apple/swift-evolution/blob/main/proposals/0389-attached-macros.md
[SE-0394]: https://github.com/apple/swift-evolution/blob/main/proposals/0394-swiftpm-expression-macros.md
[SE-0397]: https://github.com/apple/swift-evolution/blob/main/proposals/0397-freestanding-declaration-macros.md
[#64927]: <https://github.com/apple/swift/issues/64927>
[#42697]: <https://github.com/apple/swift/issues/42697>
[#42728]: <https://github.com/apple/swift/issues/42728>
@@ -9808,3 +9874,4 @@ using the `.dynamicType` member to retrieve the type of an expression should mig
[#57081]: <https://github.com/apple/swift/issues/57081>
[#57225]: <https://github.com/apple/swift/issues/57225>
[#56139]: <https://github.com/apple/swift/issues/56139>
[swift-syntax]: https://github.com/apple/swift-syntax