Swift通用参数推断错误

Question

I got swift compiler error that I cannot figure out how to fix. Plase see code snippet bellow. Compiler errors out on the last line with the message I put into commented line. Xcode 8.3.3

class View {
}

protocol FieldView {
    associatedtype Value

    var value: Value { get set }
}

class FormView<Field: View>: View where Field: FieldView {
    let fields: [Field]

    init(fields: [Field]) {
        self.fields = fields
    }
}

class BoolFieldView: View, FieldView {
    var value: Bool = false
}

class TextFieldView: View, FieldView {
    var value: String = ""
}

let fields = [BoolFieldView(), TextFieldView()]

// error: generic parameter 'Field' could not be inferred
let form = FormView(fields: fields)

Answer 1

 let fields1 = [BoolFieldView()]
 let fields2 = [TextFieldView()]

 let form1 = FormView(fields:fields1)
 let form2 = FormView(fields:fields2)

The above code can compile with Xcode 9.