SwiftUI中Type '()'无法遵循View协议问题排查（确为View代码）

我知道这个标题有点奇怪，但很多类似标题的帖子对应的问题都和我的不一样——大多是在视图里写了非View代码，但我没这么做（至少我自己是这么认为的）。我想让SwiftUI的Picker支持Int以外的BinaryInteger类型，但预览时出了问题，代码如下：

import SwiftUI

struct CompatibilityPicker<Label, SelectionValue, Content> : View where Label : StringProtocol, SelectionValue : BinaryInteger, Content : View {
    
    var content : () -> Content
    var label : Label
    
    @Binding private var _selection : SelectionValue
    
    private var selection: Binding<Int> { Binding<Int>(
        get: {
            Int(_selection)
        },
        set: {
            self._selection = SelectionValue($0)
        })
    }
    
    init(_ label : Label, selection : SelectionValue, content : @escaping () -> Content) {
        self.label = label
        self._selection = selection
        self.content = content
    }
    
    var body: some View {
        Picker(label, selection: selection, content: content)
    }
}

struct CompatibilityPicker_Previews: PreviewProvider {
    @State static var selection : UInt8 = 4
    
    static var previews: some View {
        CompatibilityPicker("Difficulty", selection: selection) { //error : Type'()' cannot conform to 'View'
            Text("Easy").tag(0)
            Text("Normal").tag(1)
            Text("Hard").tag(2)
        }
    }
}

为什么会这样？我用完全相同的语法写的常规Picker能正常运行，不知道哪里错了。

感谢@RobMayoff的解决方案，我往前推进了一步，但出现了一些就算用cmd+shift+k清理缓存也消不掉的离谱错误：

init(_ label : Label, selection : SelectionValue, @ViewBuilder content : @escaping () -> Content) {
    self.content = content
    self.label = label
    self._selection = selection //variable self._selection used before initialised
    // This stays on this line if I change the order,
} // Return from initializer without initialising all stored properties
// That is not true, as far as I can tell

内容的提问来源于stack exchange，提问作者Ter Maxima