I have a class where I want to reference a certain storage dictionary by some condition. To reduce writing the same code multiple times I wanted to use key-paths to get a writable reference to mutate in-place on self. However I hit a compile-time-error which is a little confusing.
class Test {}
class Object {
let storage: Storage
init() {
storage = Storage(branch: .init(lhs: [:], rhs: [:]))
}
func `mutate`(with condition: Bool, id: String, value: Test) {
let storagePath: WritableKeyPath = condition
? \Object.storage.branch.lhs
: \Object.storage.branch.rhs
self[keyPath: storagePath][id] = value // error: Cannot assign to immutable expression of type 'Test?
}
}
extension Object {
final class Storage {
let branch: Branch
init(branch: Branch) {
self.branch = branch
}
}
}
extension Object.Storage {
final class Branch {
var lhs: [String: Test]
var rhs: [String: Test]
init(lhs: [String: Test], rhs: [String: Test]) {
self.lhs = lhs
self.rhs = rhs
}
}
}
