SwiftUI dynamicTypeSize modifier for iOS 14, macOS 11, tvOS 14 and watchOS 7 or earlier

View+SizeCategory.swift

//
//  View+SizeCategory.swift
//
//  Created by MMP0 on 2022/02/06.
//

import SwiftUI

public extension View {
	/// Sets the Dynamic Type size within the view to the given value.
	/// (Polyfill for previous versions)
	///
	/// - SeeAlso: [`dynamicTypeSize(_:)`](https://developer.apple.com/documentation/swiftui/view/dynamictypesize%28_%3A%29-1m2tf)
	@available(iOS, introduced: 13.0, deprecated: 100000.0, renamed: "dynamicTypeSize(_:)")
	@available(macOS, introduced: 10.15, deprecated: 100000.0, renamed: "dynamicTypeSize(_:)")
	@available(tvOS, introduced: 13.0, deprecated: 100000.0, renamed: "dynamicTypeSize(_:)")
	@available(watchOS, introduced: 6.0, deprecated: 100000.0, renamed: "dynamicTypeSize(_:)")
	@available(visionOS, introduced: 1.0, deprecated: 100000.0, renamed: "dynamicTypeSize(_:)")
	func sizeCategory(_ size: ContentSizeCategory) -> some View {
		environment(\.sizeCategory, size)
	}
	
	/// Limits the Dynamic Type size within the view to the given range.
	/// (Polyfill for previous versions)
	///
	/// - SeeAlso: [`dynamicTypeSize(_:)`](https://developer.apple.com/documentation/swiftui/view/dynamictypesize%28_%3A%29-26aj0)
	@available(iOS, introduced: 13.0, deprecated: 100000.0, renamed: "dynamicTypeSize(_:)")
	@available(macOS, introduced: 10.15, deprecated: 100000.0, renamed: "dynamicTypeSize(_:)")
	@available(tvOS, introduced: 13.0, deprecated: 100000.0, renamed: "dynamicTypeSize(_:)")
	@available(watchOS, introduced: 6.0, deprecated: 100000.0, renamed: "dynamicTypeSize(_:)")
	@available(visionOS, introduced: 1.0, deprecated: 100000.0, renamed: "dynamicTypeSize(_:)")
	func sizeCategory<T: RangeExpression>(_ range: T) -> some View where T.Bound == ContentSizeCategory {
		modifier(SizeCategoryModifier(range: range))
	}
}

private struct SizeCategoryModifier: ViewModifier {
	@Environment(\.sizeCategory) private var sizeCategory
	
	private let range: ClosedRange<ContentSizeCategory>
	
	init<T: RangeExpression>(range: T) where T.Bound == ContentSizeCategory {
		self.range = range as? ClosedRange ?? {
			// Convert the range to ClosedRange
			let allCases = ContentSizeCategory.allCases.sorted()
			let lowerBound = allCases.first(where: range.contains(_:)) ?? allCases.first!
			let upperBound = allCases.last(where: range.contains(_:)) ?? allCases.last!
			return lowerBound...upperBound
		}()
	}
	
	func body(content: Content) -> some View {
		content
			.environment(\.sizeCategory, min(max(range.lowerBound, sizeCategory), range.upperBound))
	}
}

// Comparison functions are implemented by default in iOS 14, macOS 11, tvOS 14 and watchOS 7 or later.
// If you’re targeting later versions, you only need to make `ContentSizeCategory` conform to `Comparable`:
extension ContentSizeCategory: Comparable {}

// Or if not, you’ll also need the following functions:
/* public extension ContentSizeCategory {
	private var rawValue: UInt8 { unsafeBitCast(self, to: UInt8.self) }
	
	static func < (lhs: ContentSizeCategory, rhs: ContentSizeCategory) -> Bool {
		lhs.rawValue < rhs.rawValue
	}
	
	static func > (lhs: ContentSizeCategory, rhs: ContentSizeCategory) -> Bool {
		lhs.rawValue > rhs.rawValue
	}
	
	static func <= (lhs: ContentSizeCategory, rhs: ContentSizeCategory) -> Bool {
		lhs.rawValue <= rhs.rawValue
	}
	
	static func >= (lhs: ContentSizeCategory, rhs: ContentSizeCategory) -> Bool {
		lhs.rawValue >= rhs.rawValue
	}
} */

Thank you for pointing that out.
I completely forgot that the comparison functions are only available since iOS 14. I’ve updated the code.