类型“()->N”不能符合“视图”

StackOverflow上有一些标题相同的问题,但它们与我所问的无关。

我有一个按钮的高亮样式。

struct HighlightableButtonStyle<N, H>: ButtonStyle where N: View, H: View {
  
  private let alignment: Alignment
  private let normal: () -> N
  private let highlighted: () -> H
  
  init(alignment: Alignment = .center, 
       @ViewBuilder normal: @escaping () -> N,
       @ViewBuilder highlighted: @escaping () -> H) {
    self.alignment = alignment
    self.normal = normal
    self.highlighted = highlighted
  }
  
  func makeBody(configuration: Configuration) -> some View {
    configuration.label
      .frame(maxWidth: .infinity, maxHeight: .infinity)
      .contentShape(Rectangle())
      .background(alignment: alignment, content: {
        configuration.isPressed ? Color.red : Color.blue //1
      })
  }
}

我的问题是用 //1 。

如果行在is is,它编译得很好,但我想将颜色传递给样式,所以我将该行更改为

configuration.isPressed ? highlighted : normal

我得到了这个错误

Result values in '? :' expression have mismatching types '() -> H' and '() -> N'
Insert ' as! () -> N'
Type '() -> N' cannot conform to 'View'

最有趣的是最后一行。N怎么可能不符合观点呢?

我错过了什么?