Closure containing a declaration cannot be used with function builder 'ViewBuilder' - swift

Question

I cant declare a variable inside swift ui view block
var body: some View {
let isHuman = false
Text("Levels \(isHuman)")
}

Answer 1

you shouldn't create a variable inside the SwiftUI builder block, you should create it out of the body scope,
var isPlaying = false
var body: some View {
Text("Levels \(isPlaying)")
}
Swift UI uses a function builders block that can only contain content that is understandable by the builder.
Then what you should write inside the builder block is only View Type and [View] 
However, if you want to declare a variable you could work around it by introducing it to a new subclass
The purpose of this feature is to enable the creation of embedded DSLs in Swift -- allowing you to define content that gets translated to something else down the line
Also, you could use.
#State var isPlaying: Bool = false
Note
review your code twice before doing the workaround, probably you have
a misunderstanding about how swift-UI works?

Answer 2

Not so bad, you can ... another question whether you really need it, but when you really need, you do know that you can. You just need to remember that view builder must return some View and it must be same type in all possible branches
var body: some View {
let value = "" // construct somewhere or something
return Text("Levels \(value)")
}

Answer 3

When SwiftUI was first released (in 2019), the Swift language didn't allow local declarations (like let isHuman = false) inside what were then called “function builders”. However, function builders evolved into what are now called “result builders” and do support local declarations as of Swift 5.4.
This behavior is documented in SE-0289 Result Builders:
Declaration statements
Local declarations are left alone by the transformation. This allows developers to factor out subexpressions freely to clarify their code, without affecting the result builder transformation.

Answer 4

my two cents for locals AND "Expression was too complex to be solved in reasonable time”
I DO precalc in a previous nested loop.
struct MyGridView : View {
var room: Room
let MaxRows = 2
let MaxCols = 2
var body: some View {
**// precalc, as GeometryReader calls its body loop twice**
let si = FirstLevelQuestionsManager.shared
var firstLevelQuestions = FirstLevelQuestions()
let devids = room.devids
for row in 0..<self.MaxRows {
for col in 0..<self.MaxCols {
let flq = si.titleAndTextAt(row: row, col: col, ncols: self.MaxCols)
firstLevelQuestions.append(flq)
}
}
let gr = GeometryReader { (geometry : GeometryProxy) in
VStack() {
ForEach(0..<self.MaxRows) { (row: Int) in
HStack {
ForEach(0..<self.MaxCols) { (col: Int) -> GridCellView in
let index = col + row * self.MaxCols
return GridCellView(
w: (geometry.size.width / CGFloat(self.MaxCols))
titleAndText: firstLevelQuestions[index],
room: self.room,
troubleShootings: troubleShootings[index] )
}
}
}
}
} // GeometryReader
return gr
}
}