Is it possible to have an optional generic inference that obeys the View protocol?

Question

Hi! I have a custom struct that have 3 optional generic views (so I can use as Text, Navigation Item, Button or anything):

Code Block struct CustomView<FirstT: View, SecondT: View, ThirdT: View>: View {
 var view1: FirstT?
 var view2: SecondT?
 var view3: ThirdT?
 var body: some View { ... }
}

So, my the problem is when I am going to use it. Swift can't infer the type of the views, even when the are nil. How can I solve this problem?

I need this to use my init like this:

Code Block CustomView(view1: Text("Hi!"))

Currently I'm using like this:

Code Block CustomView(view1: Text("Hi!"), view2: Text(""), view3: : Text(""))

or

Code Block CustomView<Text, Text, Text>(view1: Text("Hi!"))

291

Posted by

renatafaria

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Answer 1

In Swift, nil is a context-dependent literal representing Optional<Wrapped>.none and Swift needs to infer the Wrapped type.

As a workaround, you can define type-constrained initializers.

Code Block extension CustomView where SecondT == EmptyView, ThirdT == EmptyView {
    init(view1: FirstT?)  {
        self.view1 = view1
        self.view2 = nil
        self.view3 = nil
    }
}
extension CustomView where ThirdT == EmptyView {
    init(view1: FirstT?, view2: SecondT?)  {
        self.view1 = view1
        self.view2 = view2
        self.view3 = nil
    }
}

Posted by

OOPer

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Answer 2

In Swift, nil is a context-dependent literal representing Optional<Wrapped>.none and Swift needs to infer the Wrapped type.

As a workaround, you can define type-constrained initializers.

Code Block extension CustomView where SecondT == EmptyView, ThirdT == EmptyView {
    init(view1: FirstT?)  {
        self.view1 = view1
        self.view2 = nil
        self.view3 = nil
    }
}
extension CustomView where ThirdT == EmptyView {
    init(view1: FirstT?, view2: SecondT?)  {
        self.view1 = view1
        self.view2 = view2
        self.view3 = nil
    }
}

Posted by

OOPer

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Is it possible to have an optional generic inference that obeys the View protocol?

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