Padding modifier for SwiftUI views.

PaddingModifier.swift

// NOTE: Nil values implicitly or explicitly passed as arguments to padding() are ignored.
// This differs from the built-in SwiftUI version:
//
// view.padding(trailing: nil) // has no effect
// view.padding(.trailing, nil) // resets to default
//
// See below for a version that matches the built-in behavior.

extension View {
  func padding(horizontal: CGFloat? = nil, vertical: CGFloat? = nil,
               top: CGFloat? = nil, leading: CGFloat? = nil, 
               bottom: CGFloat? = nil, trailing: CGFloat? = nil) -> some View {
    modifier(PaddingModifier(horizontal: horizontal, vertical: vertical,
                             top: top, leading: leading, 
                             bottom: bottom, trailing: trailing))
  }
}

private struct PaddingModifier: ViewModifier {
  let horizontal: CGFloat?
  let vertical: CGFloat?
  let top: CGFloat?
  let leading: CGFloat?
  let bottom: CGFloat?
  let trailing: CGFloat?

  func body(content: Content) -> some View {
    content
      .modifier(EdgePaddingModifier(.horizontal, horizontal))
      .modifier(EdgePaddingModifier(.vertical, vertical))
      .modifier(EdgePaddingModifier(.top, top))
      .modifier(EdgePaddingModifier(.leading, leading))
      .modifier(EdgePaddingModifier(.bottom, bottom))
      .modifier(EdgePaddingModifier(.trailing, trailing))
  }
}

private struct EdgePaddingModifier: ViewModifier {
  let edge: Edge.Set
  let inset: CGFloat?

  init(_ edge: Edge.Set, _ inset: CGFloat?) {
    self.edge = edge
    self.inset = inset
  }

  func body(content: Content) -> some View {
    if let inset {
      content.padding(edge, inset)
    }
    else {
      content
    }
  }
}

// This version uses .nan instead of nil for default arguments to padding() so that
// it matches the built-in behavior:
//
// view.padding(trailing: nil) // resets to default
// view.padding(.trailing, nil) // resets to default
//

extension View {
  func padding(horizontal: CGFloat? = .nan, vertical: CGFloat? = .nan,
               top: CGFloat? = .nan, leading: CGFloat? = .nan, 
               bottom: CGFloat? = .nan, trailing: CGFloat? = .nan) -> some View {
    modifier(PaddingModifier(horizontal: horizontal, vertical: vertical,
                             top: top, leading: leading, 
                             bottom: bottom, trailing: trailing))
  }
}

private struct PaddingModifier: ViewModifier {
  let horizontal: CGFloat?
  let vertical: CGFloat?
  let top: CGFloat?
  let leading: CGFloat?
  let bottom: CGFloat?
  let trailing: CGFloat?

  func body(content: Content) -> some View {
    content
      .modifier(EdgePaddingModifier(.horizontal, horizontal))
      .modifier(EdgePaddingModifier(.vertical, vertical))
      .modifier(EdgePaddingModifier(.top, top))
      .modifier(EdgePaddingModifier(.leading, leading))
      .modifier(EdgePaddingModifier(.bottom, bottom))
      .modifier(EdgePaddingModifier(.trailing, trailing))
  }
}

private struct EdgePaddingModifier: ViewModifier {
  let edge: Edge.Set
  let inset: CGFloat?

  init(_ edge: Edge.Set, _ inset: CGFloat?) {
    self.edge = edge
    self.inset = inset
  }

  func body(content: Content) -> some View {
    if inset?.isNaN ?? false {
      content
    }
    else {
      content.padding(edge, inset)
    }
  }
}