Realm 'sync' function (Swift 3)

Realm+Sync

import RealmSwift

extension Realm {
    func sync<T: Object>(_ obj: T) {
        var beganWriteTransaction = false
        if !isInWriteTransaction {
            beganWriteTransaction = true
            beginWrite()
        }
        
        if let primaryKeyName = obj.objectSchema.primaryKeyProperty?.name,
            let oldObject = object(ofType: type(of: obj), forPrimaryKey: obj.value(forKey: primaryKeyName)) {
            for property in obj.objectSchema.properties {
                if property != obj.objectSchema.primaryKeyProperty {
                    obj[property.name] = obj[property.name] ?? oldObject[property.name]
                }
            }
            obj.willFinishSync(oldObject)
        }
        add(obj, update: true)
        if beganWriteTransaction {
            try! commitWrite()
        }
    }
}

extension Object {
    func sync(_ realm: Realm = try! Realm()) {
        realm.sync(self)
    }
    
    func willFinishSync(_ oldObject: Object) {
        // Overwrite
    }
}