SwiftUI: The compiler is unable to type-check this expression in reasonable time

I want to get the calendar color from EKEvent. But i´m getting the Error: The compiler is unable to type-check this expression in reasonable time; try breaking up the expression into distinct sub-expressions The Rectangle().fill causes the Error. How do i get the UIColor from calendar.cgcolor for the Rectangle?

           ForEach(0..<data.eventsByDay.prefix(4).count)
            {(section) in
              
                HStack(alignment: .bottom){
                    ForEach(0..<data.eventsByDay[section].prefix(3).count)
                    {(row) in
                        
                        Rectangle().fill(UIColor(cgcgolor: data.eventsByDay[section][row].calendar.cgcolor))
                        .frame(width: 3, height: 26, alignment: .leading)
                        .cornerRadius(1.5)
                        .padding(.bottom, 1.0)
                    }
             }

Solution

This error occurs when Xcode cannot determine the exact cause of the error.

I suggest you the following instruction from the error

try breaking up the expression into distinct sub-expressions

You can do that by moving part of your view into a separate function or View, but also you can comment out blocks one by one until you see the actual error or until it builds: in this case, the error is on one of the commented lines.

In his case, you can comment out both ForEachs and replace them with constants:

//ForEach(0..<data.eventsByDay.prefix(4).count)
//{(section) in
    let section = 0
    HStack(alignment: .bottom){
//        ForEach(0..<data.eventsByDay[section].prefix(3).count)
//        {(row) in
            let row = 0
            Rectangle().fill(UIColor(cgcgolor: data.eventsByDay[section][row].calendar.cgcolor))
                .frame(width: 3, height: 26, alignment: .leading)
                .cornerRadius(1.5)
                .padding(.bottom, 1.0)
        }
    }
}

Then Xcode will be able to tell you that you've made a typo in the UIColor initializer(cgColor instead of cgcgolor), and that fill takes Color instead of UIColor - second one is from UIKit and with SwiftUI it will almost never will be needed.

So fixed variant looks like:

ForEach(0..<data.eventsByDay.prefix(4).count)
{(section) in
    let section = 0
    HStack(alignment: .bottom){
        ForEach(0..<data.eventsByDay[section].prefix(3).count)
        {(row) in
            let row = 0
            Rectangle().fill(Color(data.eventsByDay[section][row].calendar.cgcolor))
                .frame(width: 3, height: 26, alignment: .leading)
                .cornerRadius(1.5)
                .padding(.bottom, 1.0)
        }
    }
}