Writing Filters Using KeyPaths

Filter.swift

struct Filter<Object> {

    let path: PartialKeyPath<Object>
    let matcher: (Any) -> Bool

    init<Type>(keyPath: KeyPath<Object, Type>, matcher: @escaping (Type) -> Bool) {
        self.path = keyPath
        self.matcher = { value in
            guard let typedValue = value as? Type else { return false }
            return matcher(typedValue)
        }
    }

    func matches(_ value: Any) -> Bool {
        return matcher(value)
    }
}

class MyClass {
    let name: String
    let number: Int
    let someBool: Bool

    init(name: String, number: Int, bool: Bool) {
        self.name = name
        self.number = number
        self.someBool = bool
    }
}

let filters: [Filter<MyClass>] = [
    Filter(keyPath: \MyClass.name, matcher: { value in value == "hello"}),
    Filter(keyPath: \MyClass.number, matcher: { value in value == 3 }),
    Filter(keyPath: \MyClass.someBool, matcher: { value in value == true })
    ]

func object<T>(_ object: T, matches filters: [Filter<T>]) -> Bool {
    for filter in filters {
        guard filter.matches(object[keyPath: filter.path]) else { return false }
    }
    return true
}

let obj1 = MyClass(name: "yo", number: 3, bool: false)
let obj2 = MyClass(name: "hello", number: 3, bool: true)

print(object(obj1, matches: filters))
print(object(obj2, matches: filters))