Error message given: Generic parameter 'Data' could not be inferred - swiftui

Question

I have tried many things, but seem to be getting continuous error messages which I cannot remove. The code is listed below, and I have the following questions:
Where is the error? The second ForEach statement has no errors, but the first results in "Generic parameter 'Data' could not be inferred".
Why can't I use a "for" statement within this block? When I do so, I get an error message
It's strange not to define i and j upfront, but when I do so I get error messages. Why?
I would like to make the various (8) circle segments which are drawn buttons. I have found references in older Swift versions (see commented lines below), but how should I create those in SwiftUI?
Any help to this beginner would be much appreciated.
struct ContentView: View {
static let segmentCount = 4
static let circleCount = 2
var body: some View {
let r = CGFloat(75.0)
let center_x = CGFloat(150.0)
let center_y = CGFloat(150.0)
var arc_start = CGFloat(45.0 * CGFloat(Double.pi) / 180.0)
let arc_length = CGFloat(90.0 * CGFloat(Double.pi) / 180.0)
var arc_width = CGFloat(25.0)
let line0Target_x = center_x + r * CGFloat(cos(Double(arc_start)))
let line0Target_y = center_y + r * CGFloat(sin(Double(arc_start)))
let line1Target_x = center_x + (r + arc_width) * CGFloat(cos(Double(arc_start + arc_length)))
let line1Target_y = center_x + (r + arc_width) * CGFloat(sin(Double(arc_start + arc_length)))
ZStack {
ForEach(1..<ContentView.circleCount){ j in
r = CGFloat(25.0 + CGFloat((j) - 1.0) * 25.0)
ForEach(1..<ContentView.segmentCount){ i in
Path { path in
arc_start = CGFloat((45.0 + (CGFloat(i) - 1.0) * 90.0)) * CGFloat(Double.pi) / 180.0
path.move(to: CGPoint(x: line0Target_x, y: line0Target_y))
path.addArc(center: CGPoint(x: center_x, y: center_y), radius: r, startAngle: Angle(radians: Double(arc_start)), endAngle: Angle(radians: Double(arc_start + arc_length)), clockwise: false)
path.addLine(to: CGPoint(x: line1Target_x, y: line1Target_y))
path.addArc(center: CGPoint(x: center_x, y: center_y), radius: (r + arc_width), startAngle: Angle(radians: Double(arc_start + arc_length)), endAngle: Angle(radians: Double(arc_start)), clockwise: true)
path.addLine(to: CGPoint(x: line0Target_x, y: line0Target_y))
path.closeSubpath()
// let shapeLayer = CAShapeLayer()
// shapeLayer.strokeColor = UIColor.red.cgColor
// shapeLayer.fillColor = UIColor.blue.cgColor
// shapeLayer.path = path.cgPath
}
}
}
}
}
}

Answer 1

Your code won't compile, because you are adding lets and vars in body closure, where compiler expects some View.
You can simply move your vars inside of Path closure (or you can make some functions for computing it):
struct ContentView: View {
static let segmentCount = 4
static let circleCount = 2
var body: some View {
ZStack {
ForEach(1..<ContentView.circleCount){ j in
ForEach(1..<ContentView.segmentCount){ i in
Path { path in
let r = CGFloat(25.0 + (CGFloat(j) - 1.0) * 25.0)
let center_x = CGFloat(150.0)
let center_y = CGFloat(150.0)
var arc_start = CGFloat(45.0 * CGFloat(Double.pi) / 180.0)
let arc_length = CGFloat(90.0 * CGFloat(Double.pi) / 180.0)
var arc_width = CGFloat(25.0)
let line0Target_x = center_x + r * CGFloat(cos(Double(arc_start)))
let line0Target_y = center_y + r * CGFloat(sin(Double(arc_start)))
let line1Target_x = center_x + (r + arc_width) * CGFloat(cos(Double(arc_start + arc_length)))
let line1Target_y = center_x + (r + arc_width) * CGFloat(sin(Double(arc_start + arc_length)))
arc_start = CGFloat((45.0 + (CGFloat(i) - 1.0) * 90.0)) * CGFloat(Double.pi) / 180.0
path.move(to: CGPoint(x: line0Target_x, y: line0Target_y))
path.addArc(center: CGPoint(x: center_x, y: center_y), radius: r, startAngle: Angle(radians: Double(arc_start)), endAngle: Angle(radians: Double(arc_start + arc_length)), clockwise: false)
path.addLine(to: CGPoint(x: line1Target_x, y: line1Target_y))
path.addArc(center: CGPoint(x: center_x, y: center_y), radius: (r + arc_width), startAngle: Angle(radians: Double(arc_start + arc_length)), endAngle: Angle(radians: Double(arc_start)), clockwise: true)
path.addLine(to: CGPoint(x: line0Target_x, y: line0Target_y))
path.closeSubpath()
}
}
}
}
}
}