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A Possible Vision for Macros in Swift

As Swift evolves, it gains new language features and capabilities. There are different categories of features: some fill in gaps, taking existing syntax that is not permitted and giving it a semantics that fit well with the existing language, with features like conditional conformance or allowing existential values for protocols with Self or associated type requirements. Others introduce new capabilities or paradigms to the language, such as the addition of concurrency or comprehensive reflection.

There is another large category of language features that provide syntactic sugar to eliminate common boilerplate, taking something that can be written out in long-form and making it more concise. Such features don't technically add any expressive power to the language, because you can always write the long-form version, but their effect can be transformational if it enables use cases that would otherwise have been unwieldy. The synthesis of Codable conformances, for ex

Compiler flag: -enforce-exclusivity=<value>
Build setting: SWIFT_ENFORCE_EXCLUSIVE_ACCESS

Xcode 10.1 & Swift 4.2

Compiler default for non optimized builds if you pass no argument is the same as if you passed checked
Compiler default for optimized builds if you pass no argument is the same as if you passed unchecked

Configuration	Compiler Flag Value	Build Setting Description	Build Setting Value	Notes

	////===--- EitherSequence.swift - A sequence type-erasing two sequences -----===//
	////
	//// This source file is part of the Swift.org open source project
	////
	//// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
	//// Licensed under Apache License v2.0 with Runtime Library Exception
	////
	//// See https://swift.org/LICENSE.txt for license information
	//// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
	////

	import Combine
	import CoreFoundation
	import CoreGraphics
	import CoreText
	import Darwin
	import Foundation
	import SwiftUI
	import UIKit
	import os.log
	import os

	import Darwin

	/// A type-erasing cancellable object that executes a provided closure when canceled.
	///
	/// Subscriber implementations can use this type to provide a “cancellation token” that makes it possible for a caller to cancel a publisher, but not to use the ``Subscription`` object to request items.
	///
	/// An ``AnyCancellable`` instance automatically calls ``Cancellable/cancel()`` when deinitialized.
	@available(macOS 10.15, iOS 13.0, tvOS 13.0, watchOS 6.0, *)
	final public class AnyCancellable : Cancellable, Hashable {

	/*:
	This is a concept re-implementation of the @Binding and @State property wrappers from SwiftUI

	The only purpose of this code is to implement those wrappers myself
	just to understand how they work internally and why they are needed,

	⚠️ This is not supposed to be a reference implementation nor cover all
	subtleties of the real Binding and State types.
	The only purpose of this playground is to show how re-implementing
	them myself has helped me understand the whole thing better


	/// Conform references types for use in the COW wrapper to this protocol
	protocol Cowable: class {
	/// Make a new unique instance of `copied`
	static func makeUnique(_ copied: Self) -> Self
	}

	/// A wrapper that turns a Cowable reference type into a value-semantic
	/// type with access to all of its properties
	@dynamicMemberLookup

	// Douglas Hill, December 2018
	// Made for https://douglashill.co/reading-app/
	// Find the latest version of this file at https://github.com/douglashill/KeyboardKit

	import UIKit

	/// A table view that allows navigation and selection using a hardware keyboard.
	/// Only supports a single section.
	class KeyboardTableView: UITableView {
	// These properties may be set or overridden to provide discoverability titles for key commands.

	// Douglas Hill, October 2018

	import UIKit

	/**
	A scroll view that honours the reduce motion accessibility setting.

	If reduce motion is enabled, animated adjustments to contentOffset
	will use a cross dissolve instead of translation.