@propertyWrapper
@dynamicMemberLookup
private struct AddSubscript<T, S> {
    var wrappedValue: T

    init(wrappedValue: T, type: S.Type) {
        self.wrappedValue = wrappedValue
    }

    subscript(to type: S) -> Bool {
        get {
            return true
        }
        set {
            //some process
        }
    }

    subscript<U>(dynamicMember keyPath: WritableKeyPath<T, U>) -> U{
        get {
            return wrappedValue[keyPath: keyPath]
        }
        set {
            wrappedValue[keyPath: keyPath] = newValue
        }
    }
}

struct Test{
    @AddSubscript(type: [Int].self)
    @AddSubscript(type: String.self)
    @AddSubscript(type: Bool.self)
    @AddSubscript(type: Int.self)
    private var value = true

    func test1(){
        print(_value[to: [0]])   //it should work and it works.
        print(_value[to: ""])   //it should work and it works.


        //Error: Value of type 'Any' has no dynamic member 'subscript' using key path from root type 'Bool'
        print(_value[to: true])     //it should work but it doesn't works!
        //Error: Value of type 'Any' has no dynamic member 'subscript' using key path from root type 'Bool'
        print(_value[to: 1])      //it should work but it doesn't works!


        let keyPath: KeyPath<AddSubscript<Bool, Int>, Bool> = \.[to: 1]
        let keyPath2: KeyPath<AddSubscript<AddSubscript<Bool, Int>, Bool>, Bool> = \.[to: 1]
        let keyPath3: KeyPath<AddSubscript<AddSubscript<Bool, Int>, Bool>, Bool> = \.[to: true]
        let keyPath4: KeyPath<AddSubscript<AddSubscript<AddSubscript<Bool, Int>, Bool>, String>, Bool> = \.[to: ""]
        let keyPath5: KeyPath<AddSubscript<AddSubscript<AddSubscript<Bool, Int>, Bool>, String>, Bool> = \.[to: true]
        //Only this causes error!
        //Error: Value of type 'KeyPath<AddSubscript<AddSubscript<AddSubscript<Bool, Int>, Bool>, String>, Bool>' has no dynamic member 'subscript' using key path from root type 'Bool'
        let keyPath6: KeyPath<AddSubscript<AddSubscript<AddSubscript<Bool, Int>, Bool>, String>, Bool> = \.[to: 1]


    func test2(){
        do{
            //it works.
            let value1 = _value[dynamicMember: \.[to: ""]]
            //therefore, it should work, and it works.
            let value2 = _value[to: ""]
        }
        do{
            //it works.
            let value1 = _value[dynamicMember: \.[to: true]]
            //therefore, it should work, but doesn't work.
            //Error: Value of type '_' has no dynamic member 'subscript' using key path from root type 'Bool'
            let value2 = _value[to: true]
        }
    }
}

let value1 = value[dynamicMember: \.xxx]
let value2 = value.xxx