How to make container view in SwiftUI

Issue #450

Following the signatures of ScrollView and Group, we can create our own container

public struct ScrollView<Content> : View where Content : View {

    /// The content of the scroll view.
    public var content: Content

}

extension Group : View where Content : View {

    /// The type of view representing the body of this view.
    ///
    /// When you create a custom view, Swift infers this type from your
    /// implementation of the required `body` property.
    public typealias Body = Never

    @inlinable public init(@ViewBuilder content: () -> Content)
}

For example, below is a FullWidth that encapsulate a child element and make it full width

import SwiftUI

struct FullWidth<Content>: View where Content: View {
    let content: Content

    var body: some View {
        GeometryReader { geometry in
            self.content
                .frame(width: geometry.size.width, height: geometry.size.width, alignment: .center)
                .padding(.bottom, geometry.size.width)
        }
    }

    @inlinable public init(@ViewBuilder content: () -> Content) {
        self.content = content()
    }
}

struct FullWidth_Previews: PreviewProvider {
    static var previews: some View {
        FullWidth {
            Text("")
        }
    }
}

One problem with GeometryReader is that the size of the children can’t affect the size of its container. We need to apply Geometry at the root level

var body: some View {
    GeometryReader { geometry in
        ScrollView {
            VStack(alignment: .leading, spacing: 8) {
                Text("title")
                RemoteImage(url: self.item.url)
                    .frame(width: geometry.size.width, height: geometry.size.height, alignment: .center)
                Text("footer")
            }
        }
    }
}