aspectratio.swift

import SwiftUI

struct MySample: _ArchivableView {
    var body: some View {
        Rectangle()
    }
    
    func sizeThatFits(in proposedSize: _ProposedSize) -> CGSize {
        print(proposedSize.pretty)
        return proposedSize.orDefault
    }
}

struct ContentView: View {
    var body: some View {
        MySample()
            .aspectRatio(100/50, contentMode: .fill)
            .frame(width: 320, height: 480)
        
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

// Helpers

extension CGFloat {
    var pretty: String {
        if self == .infinity {
            return ".inf"
        } else {
            return String(format: "%.1f", self)
        }

    }
}

extension Optional where Wrapped == CGFloat {
    var pretty: String {
        self?.pretty ?? "nil"
    }
}

extension CGSize {
    var pretty: String {
        "\(width.pretty)⨉\(height.pretty)"
    }
}

extension SwiftUI._ProposedSize {
    var orDefault: CGSize {
        CGSize(width: _width ?? 10, height: _height ?? 10)
    }
    var _width: CGFloat? {
        Mirror(reflecting: self).children.first { $0.label == "width"}?.value as? CGFloat
    }
    var _height: CGFloat? {
        Mirror(reflecting: self).children.first { $0.label == "height"}?.value as? CGFloat
    }
    var pretty: String {
        return "\(_width.pretty)⨉\(_height.pretty)"
    }
}