In SwiftUI Day88 Part3, Paul wrote:

So, add this new property to CardView below its existing card property:

var removal: (() -> Void)? = nil

As you can see, that’s a closure that accepts no parameters and sends nothing back, defaulting to nil so we don’t need to provide it unless it’s explicitly needed.

Now we can replace // remove the card with a call to that closure:

self.removal?()

Tip: That question mark in there means the closure will only be called if it has been set.

Back in ContentView we can now write a method to handle removing a card, then connect it to that closure.

First, add this method that takes an index in our cards array and removes that item:

func removeCard(at index: Int) {
    cards.remove(at: index)
}

I feel challenging to understand this part of description. Would someone help me to understand how cards.remove set self.removal? or how is the mechanism of var removal: (() -> Void)? = nil ?

Thank you very much!

I did more digging, and wonder when is "self.removal" assigned a func ? By adding didSet and willSet, those lines never get printed.

var removal: (() -> Void)? = nil {
    didSet{
        print("DidSet removal")
    }
    willSet{
        print("willSet removal")
    }
}

and the value of self.removalbefore self.removal?()is called in stack view are:

removal (() -> Void)? 0x00000001022922f0 Flashzilla`partial apply forwarder for closure #1 () -> () in closure #1 (Swift.Int) -> SwiftUI.ModifiedContent<<<opaque return type of (extension in SwiftUI):SwiftUI.View.allowsHitTesting(Swift.Bool) -> some>>.0, SwiftUI.AccessibilityAttachmentModifier> in closure #1 () -> SwiftUI.ForEach<Swift.Range<Swift.Int>, Swift.Int, SwiftUI.ModifiedContent<<<opaque return type of (extension in SwiftUI):SwiftUI.View.allowsHitTesting(Swift.Bool) -> some>>.0, SwiftUI.AccessibilityAttachmentModifier>> in closure #1 () -> SwiftUI.TupleView<(SwiftUI.Spacer, <<opaque return type of (extension in SwiftUI):SwiftUI.View.background<A where A1: SwiftUI.View>(: A1, alignment: SwiftUI.Alignment) -> some>>.0, <<opaque return type of (extension in SwiftUI):SwiftUI.View.allowsHitTesting(Swift.Bool) -> some>>.0, Swift.Optional<<<opaque return type of (extension in SwiftUI):SwiftUI.View.clipShape<A where A1: SwiftUI.Shape>(: A1, style: SwiftUI.FillStyle) -> some>>.0>, SwiftUI.ConditionalContent<<<opaque return type of (extension in SwiftUI):SwiftUI.View.padding(SwiftUI.Edge.Set, Swift.Optional<CoreGraphics.CGFloat>) -> some>>.0, SwiftUI.Spacer>)> in closure #1 () -> SwiftUI.TupleView<(<<opaque return type of (extension in SwiftUI):SwiftUI.View.ignoresSafeArea(: SwiftUI.SafeAreaRegions, edges: SwiftUI.Edge.Set) -> some>>.0, <<opaque return type of (extension in SwiftUI):SwiftUI.View.onAppear(perform: Swift.Optional<() -> ()>) -> some>>.0, SwiftUI.VStack<SwiftUI.TupleView<(SwiftUI.HStack<SwiftUI.TupleView<(<<opaque return type of (extension in SwiftUI):SwiftUI.View.actionSheet(isPresented: SwiftUI.Binding<Swift.Bool>, content: () -> SwiftUI.ActionSheet) -> some>>.0, SwiftUI.Spacer, SwiftUI.Button<<<opaque return type of (extension in SwiftUI):SwiftUI.View.padding(SwiftUI.Edge.Set, Swift.Optional<CoreGraphics.CGFloat>) -> some>>.0>)>>, SwiftUI.Spacer)>>)> in Flashzilla.CardsView.body.getter : some at <compiler-generated>``

if removal contains so many values.....how doesself.removal?() call cards.removeCard(at: index)?

@roosterboy

That's all make sense now, thank you very much!