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Add ProposedViewSize and LayoutTraits API (#195)
* Add ProposedViewSize * Add LayoutTraits
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‎Sources/OpenSwiftUICore/Layout/Geometry/LayoutTraits.swift

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//
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// LayoutTraits.swift
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// OpenSwiftUICore
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//
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// Audited for iOS 18.0
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// Status: Complete
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// ID: 950FC9541E969A331FB3CF1283EA4AEC (SwiftUICore)
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package import Foundation
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/// A description of the sizing behavior of a view.
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public struct _LayoutTraits: Equatable {
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package struct FlexibilityEstimate: Comparable {
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let minLength: CGFloat
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let maxLength: CGFloat
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package init(minLength: CGFloat, maxLength: CGFloat) {
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self.minLength = minLength
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self.maxLength = maxLength
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}
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package static func < (l: _LayoutTraits.FlexibilityEstimate, r: _LayoutTraits.FlexibilityEstimate) -> Bool {
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let lDiff = l.maxLength - l.minLength
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let rDiff = r.maxLength - r.minLength
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let lEffectiveMin = lDiff == .infinity ? -l.minLength : 0
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let rEffectiveMin = rDiff == .infinity ? -r.minLength : 0
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if lDiff == rDiff {
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return lEffectiveMin < rEffectiveMin
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} else {
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return lDiff < rDiff
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}
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}
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}
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package struct Dimension : Equatable {
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package var min: CGFloat {
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didSet { _checkInvariant() }
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}
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package var ideal: CGFloat {
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didSet { _checkInvariant() }
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}
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package var max: CGFloat {
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didSet { _checkInvariant() }
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}
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package init(min: CGFloat, ideal: CGFloat, max: CGFloat) {
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self.min = min
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self.ideal = ideal
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self.max = max
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_checkInvariant()
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}
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package static func fixed(_ d: CGFloat) -> Dimension {
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Dimension(min: d, ideal: d, max: d)
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}
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private func _checkInvariant() {
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guard min >= 0,
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min.isFinite,
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ideal < .infinity,
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min <= ideal,
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ideal <= max
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else {
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preconditionFailure("malformed dimension \(self)")
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}
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}
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}
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package var width = Dimension(min: .zero, ideal: .zero, max: .infinity)
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package var height = Dimension(min: .zero, ideal: .zero, max: .infinity)
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package init() {}
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package init(width: Dimension, height: Dimension) {
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self.width = width
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self.height = height
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}
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package subscript(axis: Axis) -> Dimension {
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get { axis == .horizontal ? width : height }
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set { if axis == .horizontal { width = newValue } else { height = newValue } }
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}
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}
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@available(*, unavailable)
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extension _LayoutTraits: Sendable {}
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extension _LayoutTraits {
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package init(width: CGFloat, height: CGFloat) {
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self.width = .fixed(width)
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self.height = .fixed(height)
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}
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package init(_ size: CGSize) {
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self.init(width: size.width, height: size.height)
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}
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}
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extension _LayoutTraits: CustomStringConvertible {
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public var description: String {
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"(\(width), \(height)"
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}
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}
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extension _LayoutTraits.Dimension: CustomStringConvertible {
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package var description: String {
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if min == max {
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"\(min)"
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} else {
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"\(min)...\(ideal)...\(max)"
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}
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}
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}
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extension _LayoutTraits {
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package var idealSize: CGSize {
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get {
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CGSize(width: width.ideal, height: height.ideal)
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}
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set {
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width.ideal = newValue.width
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height.ideal = newValue.height
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}
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}
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package var minSize: CGSize {
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get {
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CGSize(width: width.min, height: height.min)
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}
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set {
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width.min = newValue.width
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height.min = newValue.height
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}
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}
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package var maxSize: CGSize {
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get {
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CGSize(width: width.max, height: height.max)
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}
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set {
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width.max = newValue.width
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height.max = newValue.height
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}
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}
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}
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extension CGSize {
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package func clamped(to constraints: _LayoutTraits) -> CGSize {
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CGSize(
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width: width.clamp(min: constraints.width.min, max: constraints.width.max),
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height: height.clamp(min: constraints.height.min, max: constraints.height.max)
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)
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}
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}

‎Sources/OpenSwiftUICore/Layout/View/ProposedViewSize.swift

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//
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// ProposedViewSize.swift
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// OpenSwiftUICore
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//
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// Audited for iOS 18.0
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// Status: Complete
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public import Foundation
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#if canImport(Darwin)
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public import CoreGraphics
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#endif
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/// A proposal for the size of a view.
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///
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/// During layout in OpenSwiftUI, views choose their own size, but they do that
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/// in response to a size proposal from their parent view. When you create
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/// a custom layout using the ``Layout`` protocol, your layout container
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/// participates in this process using `ProposedViewSize` instances.
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/// The layout protocol's methods take a proposed size input that you
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/// can take into account when arranging views and calculating the size of
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/// the composite container. Similarly, your layout proposes a size to each
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/// of its own subviews when it measures and places them.
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///
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/// Layout containers typically measure their subviews by proposing several
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/// sizes and looking at the responses. The container can use this information
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/// to decide how to allocate space among its subviews. A
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/// layout might try the following special proposals:
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///
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/// * The ``zero`` proposal; the view responds with its minimum size.
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/// * The ``infinity`` proposal; the view responds with its maximum size.
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/// * The ``unspecified`` proposal; the view responds with its ideal size.
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///
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/// A layout might also try special cases for one dimension at a time. For
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/// example, an ``HStack`` might measure the flexibility of its subviews'
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/// widths, while using a fixed value for the height.
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@frozen
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public struct ProposedViewSize: Equatable {
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/// The proposed horizontal size measured in points.
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///
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/// A value of `nil` represents an unspecified width proposal, which a view
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/// interprets to mean that it should use its ideal width.
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public var width: CGFloat?
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/// The proposed vertical size measured in points.
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///
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/// A value of `nil` represents an unspecified height proposal, which a view
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/// interprets to mean that it should use its ideal height.
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public var height: CGFloat?
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/// A size proposal that contains zero in both dimensions.
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///
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/// Subviews of a custom layout return their minimum size when you propose
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/// this value using the ``LayoutSubview/dimensions(in:)`` method.
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/// A custom layout should also return its minimum size from the
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/// ``Layout/sizeThatFits(proposal:subviews:cache:)`` method for this
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/// value.
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public static let zero: ProposedViewSize = .init(width: .zero, height: .zero)
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/// The proposed size with both dimensions left unspecified.
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///
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/// Both dimensions contain `nil` in this size proposal.
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/// Subviews of a custom layout return their ideal size when you propose
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/// this value using the ``LayoutSubview/dimensions(in:)`` method.
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/// A custom layout should also return its ideal size from the
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/// ``Layout/sizeThatFits(proposal:subviews:cache:)`` method for this
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/// value.
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public static let unspecified: ProposedViewSize = .init(width: nil, height: nil)
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/// A size proposal that contains infinity in both dimensions.
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///
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/// Both dimensions contain
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/// [infinity](https://developer.apple.com/documentation/CoreFoundation/CGFloat/1454161-infinity)
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/// in this size proposal.
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/// Subviews of a custom layout return their maximum size when you propose
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/// this value using the ``LayoutSubview/dimensions(in:)`` method.
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/// A custom layout should also return its maximum size from the
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/// ``Layout/sizeThatFits(proposal:subviews:cache:)`` method for this
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/// value.
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public static let infinity: ProposedViewSize = .init(width: .infinity, height: .infinity)
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/// Creates a new proposed size using the specified width and height.
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///
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/// - Parameters:
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/// - width: A proposed width in points. Use a value of `nil` to indicate
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/// that the width is unspecified for this proposal.
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/// - height: A proposed height in points. Use a value of `nil` to
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/// indicate that the height is unspecified for this proposal.
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@inlinable
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public init(width: CGFloat?, height: CGFloat?) {
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(self.width, self.height) = (width, height)
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}
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package init(_ proposal: _ProposedSize) {
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width = proposal.width
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height = proposal.height
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}
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/// Creates a new proposed size from a specified size.
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///
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/// - Parameter size: A proposed size with dimensions measured in points.
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@inlinable
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public init(_ size: CGSize) {
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self.init(width: size.width, height: size.height)
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}
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/// Creates a new proposal that replaces unspecified dimensions in this
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/// proposal with the corresponding dimension of the specified size.
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///
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/// Use the default value to prevent a flexible view from disappearing
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/// into a zero-sized frame, and ensure the unspecified value remains
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/// visible during debugging.
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///
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/// - Parameter size: A set of concrete values to use for the size proposal
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/// in place of any unspecified dimensions. The default value is `10`
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/// for both dimensions.
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///
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/// - Returns: A new, fully specified size proposal.
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@inlinable
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public func replacingUnspecifiedDimensions(by size: CGSize = CGSize(width: 10, height: 10)) -> CGSize {
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CGSize(width: width ?? size.width, height: height ?? size.height)
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}
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package init(_ major: CGFloat?, in axis: Axis, by minor: CGFloat?) {
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self = axis == .horizontal ? ProposedViewSize(width: major, height: minor) : ProposedViewSize(width: minor, height: major)
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}
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package subscript(axis: Axis) -> CGFloat? {
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get { axis == .horizontal ? width : height }
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set { if axis == .horizontal { width = newValue } else { height = newValue } }
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}
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}
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extension _ProposedSize {
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package init(_ p: ProposedViewSize) {
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self.init(width: p.width, height: p.height)
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}
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}

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