Feature request: Making placeholder can receive a ViewBuilder

[dreampiggy]

Current public API, use Image or UIImage as a placeholder, which is previouslly in UIKit world. But is not suitable in SwiftUI world.

For SwiftUI, the view is a command to build real view on the screen, there are no subviews like UIKit. So, putting a Image is not so comfortable.

For example, if I want to add a grey-rounded corner placeholder, I don't need to use a Image, but a native Rectangle view.

Usage code:

WebImage(url: url) {
    Rectangle()
    .foregroundColor(.gray)
}

[dreampiggy]

Current my success progress, by changing Public API to like this:

public init(url: URL?, options: SDWebImageOptions = [], context: [SDWebImageContextOption : Any]? = nil, @ViewBuilder placeholder: @escaping () -> AnyView)

Using like this

WebImage(url: url) {
    AnyView(Rectangle()
    .foregroundColor(.gray))
}

[dreampiggy]

However, I have no idea how to make it possible to use both syntax:

WebImage(url: url) {
    Rectangle()
    .foregroundColor(.gray)
}

and

WebImage(url: url)

Because the SwiftUI using the generatic type like public struct ZStack<Content> : View where Content : View. So that the @viewBuilder can ensure the type is the Content.

However, for us, we want to support both of the syntax above, which means the return type of @viewBuilder should be generatic as well. No idea how to do this.

If I put the same design pattern, the usage may looks ugly:

WebImage(url: url) // Compile Error !
WebImage<Image>(url: url) // Works but ugly
WebImage(url: url) {
    Rectangle()
    .foregroundColor(.gray) // Swift Compiler calculate the return type to `Rectangle`, which means the generaic type is WebImage<Rectangle>
}

[dreampiggy]

If this is not possible, a temp solution, we support placeholder to be a View, but not Image. Simple solution :)