diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index b991de4..a92de46 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -1,63 +1,63 @@
 set(kasync_SRCS
     future.cpp
     debug.cpp
 )
 
 set(kasync_priv_HEADERS
     continuations_p.h
     execution_p.h
     executor_p.h
-    async_impl.h
     job_impl.h
+    traits_p.h
     debug.h
 )
 
 ecm_generate_headers(kasync_HEADERS
     HEADER_NAMES
     Async
     Future
     REQUIRED_HEADERS kasync_HEADERS
 )
 
 
 add_library(KAsync ${kasync_SRCS})
 
 generate_export_header(KAsync BASE_NAME kasync)
 
 target_include_directories(KAsync INTERFACE "$<INSTALL_INTERFACE:${KDE_INSTALL_INCLUDEDIR}/KAsync>")
 target_include_directories(KAsync PUBLIC "$<BUILD_INTERFACE:${KAsync_SOURCE_DIR}/src>")
 
 target_link_libraries(KAsync
     PUBLIC
         Qt5::Core
 )
 
 
 set_target_properties(KAsync PROPERTIES
     VERSION ${KASYNC_VERSION_STRING}
     SOVERSION ${KASYNC_SOVERSION}
     EXPORT_NAME KAsync
 )
 
 ecm_generate_pri_file(BASE_NAME KAsync
     LIB_NAME KAsync
     FILENAME_VAR PRI_FILENAME
 )
 
 install(TARGETS
     KAsync
     EXPORT KAsyncTargets ${KDE_INSTALL_TARGETS_DEFAULT_ARGS}
 )
 
 install(FILES
     ${CMAKE_CURRENT_BINARY_DIR}/kasync_export.h
     ${kasync_HEADERS}
     ${kasync_priv_HEADERS}
     DESTINATION ${KDE_INSTALL_INCLUDEDIR}/KAsync
     COMPONENT Devel
 )
 
 install(FILES
     ${PRI_FILENAME}
     DESTINATION ${ECM_MKSPECS_INSTALL_DIR}
 )
diff --git a/src/async.h b/src/async.h
index 6b68460..49f345c 100644
--- a/src/async.h
+++ b/src/async.h
@@ -1,587 +1,586 @@
 /*
  * Copyright 2014 - 2015 Daniel Vrátil <dvratil@redhat.com>
  * Copyright 2016  Daniel Vrátil <dvratil@kde.org>
  * Copyright 2016  Christian Mollekopf <mollekopf@kolabsystems.com>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public License as
  * published by the Free Software Foundation; either version 2 of
  * the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library. If not, see <http://www.gnu.org/licenses/>.
  */
 
 #ifndef KASYNC_H
 #define KASYNC_H
 
 #include "kasync_export.h"
 
 #include <functional>
 #include <type_traits>
 #include <cassert>
 
 #include "future.h"
 #include "debug.h"
 
-#include "async_impl.h"
 #include "continuations_p.h"
 #include "executor_p.h"
 
 class QObject;
 
 /**
  * @mainpage KAsync
  *
  * @brief API to help write async code.
  *
  * This API is based around jobs that take lambdas to execute asynchronous tasks.
  * Each async operation can take a continuation that can then be used to execute
  * further async operations. That way it is possible to build async chains of
  * operations that can be stored and executed later on. Jobs can be composed,
  * similarly to functions.
  *
  * Relations between the components:
  * * Job: API wrapper around Executors chain. Can be destroyed while still running,
  *        because the actual execution happens in the background
  * * Executor: Describes task to execute. Executors form a linked list matching the
  *        order in which they will be executed. The Executor chain is destroyed when
  *        the parent Job is destroyed. However if the Job is still running it is
  *        guaranteed that the Executor chain will not be destroyed until the execution
  *        is finished.
  * * Execution: The running execution of the task stored in Executor. Each call to
  *        Job::exec() instantiates new Execution chain, which makes it possible for
  *        the Job to be executed multiple times (even in parallel).
  * * Future: Representation of the result that is being calculated
  *
  *
  * TODO: Possibility to abort a job through future (perhaps optional?)
  * TODO: Support for timeout, specified during exec call, after which the error
  *       handler gets called with a defined errorCode.
  */
 
 
 namespace KAsync {
 
 template<typename PrevOut, typename Out, typename ... In>
 class Executor;
 
 class JobBase;
 
 template<typename Out, typename ... In>
 class Job;
 
 //@cond PRIVATE
 namespace Private {
 
 template<typename Out, typename ... In>
 Job<Out, In ...> startImpl(Private::ContinuationHolder<Out, In ...> &&helper)
 {
     static_assert(sizeof...(In) <= 1, "Only one or zero input parameters are allowed.");
     return Job<Out, In...>(QSharedPointer<Private::Executor<Out, In ...>>::create(
                 std::forward<Private::ContinuationHolder<Out, In...>>(helper), nullptr, Private::ExecutionFlag::GoodCase));
 }
 
 } // namespace Private
 //@endcond
 
 
 /**
  * @relates Job
  *
  * Start an asynchronous job sequence.
  *
  * start() is your starting point to build a chain of jobs to be executed
  * asynchronously.
  *
  * @param func A continuation to be executed.
  */
 
 ///Sync continuation without job: [] () -> T { ... }
 template<typename Out = void, typename ... In, typename F>
 auto start(F &&func) -> std::enable_if_t<!std::is_base_of<JobBase, decltype(func(std::declval<In>() ...))>::value,
                                          Job<decltype(func(std::declval<In>() ...)), In...>>
 {
     static_assert(sizeof...(In) <= 1, "Only one or zero input parameters are allowed.");
     return Private::startImpl<Out, In...>(Private::ContinuationHolder<Out, In ...>(SyncContinuation<Out, In ...>(std::forward<F>(func))));
 }
 
 ///continuation with job: [] () -> KAsync::Job<...> { ... }
 template<typename Out = void, typename ... In, typename F>
 auto start(F &&func) -> std::enable_if_t<std::is_base_of<JobBase, decltype(func(std::declval<In>() ...))>::value,
                                          Job<typename decltype(func(std::declval<In>() ...))::OutType, In...>>
 {
     static_assert(sizeof...(In) <= 1, "Only one or zero input parameters are allowed.");
     return Private::startImpl<Out, In...>(Private::ContinuationHolder<Out, In ...>(JobContinuation<Out, In...>(std::forward<F>(func))));
 }
 
 ///Handle continuation: [] (KAsync::Future<T>, ...) { ... }
 template<typename Out = void, typename ... In>
 auto start(AsyncContinuation<Out, In ...> &&func) -> Job<Out, In ...>
 {
     static_assert(sizeof...(In) <= 1, "Only one or zero input parameters are allowed.");
     return Private::startImpl<Out, In...>(Private::ContinuationHolder<Out, In ...>(std::forward<AsyncContinuation<Out, In ...>>(func)));
 }
 
 enum ControlFlowFlag {
     Break,
     Continue
 };
 
 /**
  * @relates Job
  *
  * Async while loop.
  *
  * Loop continues while body returns ControlFlowFlag::Continue.
  */
 KASYNC_EXPORT Job<void> doWhile(const Job<ControlFlowFlag> &body);
 
 /**
  * @relates Job
  *
  * Async while loop.
  *
  * Shorthand that takes a continuation.
  *
  * @see doWhile
  */
 KASYNC_EXPORT Job<void> doWhile(const JobContinuation<ControlFlowFlag> &body);
 
 
 
 /**
  * @relates Job
  *
  * Async delay.
  */
 KASYNC_EXPORT Job<void> wait(int delay);
 
 /**
  * @relates Job
  *
  * A null job.
  *
  * An async noop.
  *
  */
 template<typename Out = void>
 Job<Out> null();
 
 /**
  * @relates Job
  *
  * Async value.
  */
 template<typename Out>
 Job<Out> value(Out);
 
 /**
  * @relates Job
  *
  * Async foreach loop.
  *
  * This will execute a job for every value in the list.
  * Errors while not stop processing of other jobs but set an error on the wrapper job.
  */
 template<typename List, typename ValueType = typename List::value_type>
 Job<void, List> forEach(KAsync::Job<void, ValueType> job);
 
 /**
  * @relates Job
  *
  * Async foreach loop.
  *
  * Shorthand that takes a continuation.
  *
  * @see serialForEach
  */
 template<typename List, typename ValueType = typename List::value_type>
  Job<void, List> forEach(JobContinuation<void, ValueType> &&);
 
 
 /**
  * @relates Job
  *
  * Serial Async foreach loop.
  *
  * This will execute a job for every value in the list sequentially.
  * Errors while not stop processing of other jobs but set an error on the wrapper job.
  */
 template<typename List, typename ValueType = typename List::value_type>
 Job<void, List> serialForEach(KAsync::Job<void, ValueType> job);
 
 /**
  * @relates Job
  *
  * Serial Async foreach loop.
  *
  * Shorthand that takes a continuation.
  *
  * @see serialForEach
  */
 template<typename List, typename ValueType = typename List::value_type>
 Job<void, List> serialForEach(JobContinuation<void, ValueType> &&);
 
 
 /**
  * @relates Job
  *
  * An error job.
  *
  * An async error.
  *
  */
 template<typename Out = void>
 Job<Out> error(int errorCode = 1, const QString &errorMessage = QString());
 
 /**
  * @relates Job
  *
  * An error job.
  *
  * An async error.
  *
  */
 template<typename Out = void>
 Job<Out> error(const char *);
 
 /**
  * @relates Job
  *
  * An error job.
  *
  * An async error.
  *
  */
 template<typename Out = void>
 Job<Out> error(const Error &);
 
 //@cond PRIVATE
 class KASYNC_EXPORT JobBase
 {
     template<typename Out, typename ... In>
     friend class Job;
 
 public:
     explicit JobBase(const Private::ExecutorBasePtr &executor)
         : mExecutor(executor)
     {}
 
     virtual ~JobBase() = default;
 
 protected:
     Private::ExecutorBasePtr mExecutor;
 };
 //@endcond
 
 /**
  * @brief An Asynchronous job
  *
  * A single instance of Job represents a single method that will be executed
  * asynchronously. The Job is started by exec(), which returns Future
  * immediatelly. The Future will be set to finished state once the asynchronous
  * task has finished. You can use Future::waitForFinished() to wait for
  * for the Future in blocking manner.
  *
  * It is possible to chain multiple Jobs one after another in different fashion
  * (sequential, parallel, etc.). Calling exec() will then return a pending
  * Future, and will execute the entire chain of jobs.
  *
  * @code
  * auto job = Job::start<QList<int>>(
  *     [](KAsync::Future<QList<int>> &future) {
  *         MyREST::PendingUsers *pu = MyREST::requestListOfUsers();
  *         QObject::connect(pu, &PendingOperation::finished,
  *                          [&](PendingOperation *pu) {
  *                              future->setValue(dynamic_cast<MyREST::PendingUsers*>(pu)->userIds());
  *                              future->setFinished();
  *                          });
  *      })
  * .each<QList<MyREST::User>, int>(
  *      [](const int &userId, KAsync::Future<QList<MyREST::User>> &future) {
  *          MyREST::PendingUser *pu = MyREST::requestUserDetails(userId);
  *          QObject::connect(pu, &PendingOperation::finished,
  *                           [&](PendingOperation *pu) {
  *                              future->setValue(Qlist<MyREST::User>() << dynamic_cast<MyREST::PendingUser*>(pu)->user());
  *                              future->setFinished();
  *                           });
  *      });
  *
  * KAsync::Future<QList<MyREST::User>> usersFuture = job.exec();
  * usersFuture.waitForFinished();
  * QList<MyRest::User> users = usersFuture.value();
  * @endcode
  *
  * In the example above, calling @p job.exec() will first invoke the first job,
  * which will retrieve a list of IDs and then will invoke the second function
  * for each single entry in the list returned by the first function.
  */
 template<typename Out, typename ... In>
 class Job : public JobBase
 {
     //@cond PRIVATE
     template<typename OutOther, typename ... InOther>
     friend class Job;
 
     template<typename OutOther, typename ... InOther>
     friend Job<OutOther, InOther ...> Private::startImpl(Private::ContinuationHolder<OutOther, InOther ...> &&);
 
     template<typename List, typename ValueType>
     friend  Job<void, List> forEach(KAsync::Job<void, ValueType> job);
 
     template<typename List, typename ValueType>
     friend Job<void, List> serialForEach(KAsync::Job<void, ValueType> job);
 
     // Used to disable implicit conversion of Job<void to Job<void> which triggers
     // comiler warning.
     struct IncompleteType;
     //@endcond
 
 public:
     typedef Out OutType;
 
     ///A continuation
     template<typename OutOther, typename ... InOther>
     Job<OutOther, In ...> then(const Job<OutOther, InOther ...> &job) const;
 
     ///Shorthands for a job that returns another job from it's continuation
     //
     //OutOther and InOther are only there fore backwards compatibility, but are otherwise ignored.
     //It should never be neccessary to specify any template arguments, as they are automatically deduced from the provided argument.
     //
     //We currently have to write a then overload for:
     //* One argument in the continuation
     //* No argument in the continuation
     //* One argument + error in the continuation
     //* No argument + error in the continuation
     //This is due to how we extract the return type with "decltype(func(std::declval<Out>()))".
     //Ideally we could conflate this into at least fewer overloads, but I didn't manage so far and this at least works as expected.
 
     ///Continuation returning job: [] (Arg) -> KAsync::Job<...> { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<std::is_base_of<JobBase, decltype(func(std::declval<Out>()))>::value,
                                                   Job<typename decltype(func(std::declval<Out>()))::OutType, In...>>
     {
         using ResultJob = decltype(func(std::declval<Out>())); //Job<QString, int>
         return thenImpl<typename ResultJob::OutType, Out>(
                 {JobContinuation<typename ResultJob::OutType, Out>(std::forward<F>(func))}, Private::ExecutionFlag::GoodCase);
     }
 
     ///Void continuation with job: [] () -> KAsync::Job<...> { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<std::is_base_of<JobBase, decltype(func())>::value,
                                                   Job<typename decltype(func())::OutType, In...>>
     {
         using ResultJob = decltype(func()); //Job<QString, void>
         return thenImpl<typename ResultJob::OutType>(
                 {JobContinuation<typename ResultJob::OutType>(std::forward<F>(func))}, Private::ExecutionFlag::GoodCase);
     }
 
     ///Error continuation returning job: [] (KAsync::Error, Arg) -> KAsync::Job<...> { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<std::is_base_of<JobBase, decltype(func(KAsync::Error{}, std::declval<Out>()))>::value,
                                                   Job<typename decltype(func(KAsync::Error{}, std::declval<Out>()))::OutType, In...>>
     {
         using ResultJob = decltype(func(KAsync::Error{}, std::declval<Out>())); //Job<QString, int>
         return thenImpl<typename ResultJob::OutType, Out>(
                 {JobErrorContinuation<typename ResultJob::OutType, Out>(std::forward<F>(func))}, Private::ExecutionFlag::Always);
     }
 
     ///Error void continuation returning job: [] (KAsync::Error) -> KAsync::Job<...> { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<std::is_base_of<JobBase, decltype(func(KAsync::Error{}))>::value,
                                                   Job<typename decltype(func(KAsync::Error{}))::OutType, In...>>
     {
         using ResultJob = decltype(func(KAsync::Error{}));
         return thenImpl<typename ResultJob::OutType>(
                 {JobErrorContinuation<typename ResultJob::OutType>(std::forward<F>(func))}, Private::ExecutionFlag::Always);
     }
 
     ///Sync continuation: [] (Arg) -> void { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<!std::is_base_of<JobBase, decltype(func(std::declval<Out>()))>::value,
                                                   Job<decltype(func(std::declval<Out>())), In...>>
     {
         using ResultType = decltype(func(std::declval<Out>())); //QString
         return thenImpl<ResultType, Out>(
                 {SyncContinuation<ResultType, Out>(std::forward<F>(func))}, Private::ExecutionFlag::GoodCase);
     }
 
     ///Sync void continuation: [] () -> void { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<!std::is_base_of<JobBase, decltype(func())>::value,
                                                   Job<decltype(func()), In...>>
     {
         using ResultType = decltype(func()); //QString
         return thenImpl<ResultType>(
                 {SyncContinuation<ResultType>(std::forward<F>(func))}, Private::ExecutionFlag::GoodCase);
     }
 
     ///Sync error continuation: [] (KAsync::Error, Arg) -> void { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<!std::is_base_of<JobBase, decltype(func(KAsync::Error{}, std::declval<Out>()))>::value,
                                                   Job<decltype(func(KAsync::Error{}, std::declval<Out>())),In...>>
     {
         using ResultType = decltype(func(KAsync::Error{}, std::declval<Out>())); //QString
         return thenImpl<ResultType, Out>(
                 {SyncErrorContinuation<ResultType, Out>(std::forward<F>(func))}, Private::ExecutionFlag::Always);
     }
 
     ///Sync void error continuation: [] (KAsync::Error) -> void { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<!std::is_base_of<JobBase, decltype(func(KAsync::Error{}))>::value,
                                                   Job<decltype(func(KAsync::Error{})), In...>>
     {
         using ResultType = decltype(func(KAsync::Error{}));
         return thenImpl<ResultType>(
                 {SyncErrorContinuation<ResultType>(std::forward<F>(func))}, Private::ExecutionFlag::Always);
     }
 
     ///Shorthand for a job that receives the error and a handle
     template<typename OutOther, typename ... InOther>
     Job<OutOther, In ...> then(AsyncContinuation<OutOther, InOther ...> &&func) const
     {
         return thenImpl<OutOther, InOther ...>({std::forward<AsyncContinuation<OutOther, InOther ...>>(func)},
                                                Private::ExecutionFlag::GoodCase);
     }
 
     ///Shorthand for a job that receives the error and a handle
     template<typename OutOther, typename ... InOther>
     Job<OutOther, In ...> then(AsyncErrorContinuation<OutOther, InOther ...> &&func) const
     {
         return thenImpl<OutOther, InOther ...>({std::forward<AsyncErrorContinuation<OutOther, InOther ...>>(func)}, Private::ExecutionFlag::Always);
     }
 
     ///Shorthand for a job that receives the error only
     Job<Out, In ...> onError(SyncErrorContinuation<void> &&errorFunc) const;
 
     /**
      * Shorthand for a forEach loop that automatically uses the return type of
      * this job to deduce the type exepected.
      */
     template<typename OutOther = void, typename ListType = Out, typename ValueType = typename ListType::value_type, std::enable_if_t<!std::is_void<ListType>::value, int> = 0>
     Job<void, In ...> each(JobContinuation<void, ValueType> &&func) const
     {
         eachInvariants<OutOther>();
         return then<void, In ...>(forEach<Out, ValueType>(std::forward<JobContinuation<void, ValueType>>(func)));
     }
 
     /**
      * Shorthand for a serialForEach loop that automatically uses the return type
      * of this job to deduce the type exepected.
      */
     template<typename OutOther = void, typename ListType = Out, typename ValueType = typename ListType::value_type, std::enable_if_t<!std::is_void<ListType>::value, int> = 0>
     Job<void, In ...> serialEach(JobContinuation<void, ValueType> &&func) const
     {
         eachInvariants<OutOther>();
         return then<void, In ...>(serialForEach<Out, ValueType>(std::forward<JobContinuation<void, ValueType>>(func)));
     }
 
     /**
      * Enable implicit conversion to Job<void>.
      *
      * This is necessary in assignments that only use the return value (which is the normal case).
      * This avoids constructs like:
      * auto job = KAsync::start<int>( ... )
      *  .then<void, int>( ... )
      *  .then<void>([](){}); //Necessary for the assignment without the implicit conversion
      */
     template<typename ... InOther>
     operator std::conditional_t<std::is_void<OutType>::value, IncompleteType, Job<void>>();
 
     /**
      * Adds an unnamed value to the context.
      * The context is guaranteed to persist until the jobs execution has finished.
      *
      * Useful for setting smart pointer to manage lifetime of objects required
      * during the execution of the job.
      */
     template<typename T>
     Job<Out, In ...> &addToContext(const T &value)
     {
         assert(mExecutor);
         mExecutor->addToContext(QVariant::fromValue<T>(value));
         return *this;
     }
 
     /**
      * Adds a guard.
      * It is guaranteed that no callback is executed after the guard vanishes.
      *
      * Use this i.e. ensure you don't call-back into an already destroyed object.
      */
     Job<Out, In ...> &guard(const QObject *o)
     {
         assert(mExecutor);
         mExecutor->guard(o);
         return *this;
     }
 
     /**
      * @brief Starts execution of the job chain.
      *
      * This will start the execution of the task chain, starting from the
      * first one. It is possible to call this function multiple times, each
      * invocation will start a new processing and provide a new Future to
      * watch its status.
      *
      * @param in Argument to be passed to the very first task
      * @return Future&lt;Out&gt; object which will contain result of the last
      * task once if finishes executing. See Future documentation for more details.
      *
      * @see exec(), Future
      */
     template<typename FirstIn>
     KAsync::Future<Out> exec(FirstIn in);
 
     /**
      * @brief Starts execution of the job chain.
      *
      * This will start the execution of the task chain, starting from the
      * first one. It is possible to call this function multiple times, each
      * invocation will start a new processing and provide a new Future to
      * watch its status.
      *
      * @return Future&lt;Out&gt; object which will contain result of the last
      * task once if finishes executing. See Future documentation for more details.
      *
      * @see exec(FirstIn in), Future
      */
     KAsync::Future<Out> exec();
 
     explicit Job(JobContinuation<Out, In ...> &&func);
     explicit Job(AsyncContinuation<Out, In ...> &&func);
 
 private:
     //@cond PRIVATE
     explicit Job(Private::ExecutorBasePtr executor);
 
     template<typename OutOther, typename ... InOther>
     Job<OutOther, In ...> thenImpl(Private::ContinuationHolder<OutOther, InOther ...> helper,
                                    Private::ExecutionFlag execFlag = Private::ExecutionFlag::GoodCase) const;
 
     template<typename InOther, typename ... InOtherTail>
     void thenInvariants() const;
 
     //Base case for an empty parameter pack
     template<typename ... InOther>
     auto thenInvariants() const -> std::enable_if_t<(sizeof...(InOther) == 0)>;
 
     template<typename OutOther>
     void eachInvariants() const;
     //@endcond
 };
 
 } // namespace KAsync
 
 
 // out-of-line definitions of Job methods
 #include "job_impl.h"
 
 #endif // KASYNC_H
diff --git a/src/async_impl.h b/src/async_impl.h
deleted file mode 100644
index 425ad5e..0000000
--- a/src/async_impl.h
+++ /dev/null
@@ -1,103 +0,0 @@
-/*
- * Copyright 2014 - 2015 Daniel Vrátil <dvratil@redhat.com>
- * Copyright 2016        Daniel Vrátil <dvratil@kde.org>
- *
- * This library is free software; you can redistribute it and/or
- * modify it under the terms of the GNU Library General Public License as
- * published by the Free Software Foundation; either version 2 of
- * the License, or (at your option) any later version.
- *
- * This library is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU Library General Public License for more details.
- *
- * You should have received a copy of the GNU Library General Public License
- * along with this library. If not, see <http://www.gnu.org/licenses/>.
- */
-
-#ifndef KASYNC_IMPL_H
-#define KASYNC_IMPL_H
-
-#include <type_traits>
-#include <tuple>
-
-//@cond PRIVATE
-
-namespace KAsync {
-
-template<typename T>
-class Future;
-
-namespace detail {
-
-template<typename T, typename Enable = void>
-struct isIterable {
-    enum { value = 0 };
-};
-
-template<typename T>
-struct isIterable<T, std::conditional_t<false, typename T::iterator, void>> {
-    enum { value = 1 };
-};
-
-template<typename ... T>
-struct prevOut {
-    using type = std::tuple_element_t<0, std::tuple<T ..., void>>;
-};
-
-template<typename T, typename Out, typename ... In>
-struct funcHelper {
-    using type = void(T::*)(In ..., KAsync::Future<Out> &);
-};
-
-template<typename T, typename Out, typename ... In>
-struct syncFuncHelper {
-    using type =  Out(T::*)(In ...);
-};
-
-template<typename T,
-         class = std::enable_if_t<!std::is_void<T>::value>,
-         class = std::enable_if_t<std::is_move_constructible<T>::value>>
-void copyFutureValue(KAsync::Future<T> &in, KAsync::Future<T> &out)
-{
-    out.setValue(std::move(in.value()));
-}
-
-template<typename T,
-         class = std::enable_if_t<!std::is_void<T>::value>,
-         class = std::enable_if_t<!std::is_move_constructible<T>::value>,
-         class = std::enable_if_t<std::is_copy_constructible<T>::value>>
-void copyFutureValue(const KAsync::Future<T> &in, KAsync::Future<T> &out)
-{
-    out.setValue(in.value());
-}
-
-template<typename T>
-inline std::enable_if_t<std::is_void<T>::value, void>
-copyFutureValue(const KAsync::Future<T> &/* in */, KAsync::Future<T> &/* out */)
-{
-    // noop
-}
-
-template<typename T>
-inline std::enable_if_t<!std::is_void<T>::value, void>
-aggregateFutureValue(const KAsync::Future<T> &in, KAsync::Future<T> &out)
-{
-    out.setValue(out.value() + in.value());
-}
-
-template<typename T>
-inline std::enable_if_t<std::is_void<T>::value, void>
-aggregateFutureValue(const KAsync::Future<T> & /*in */, KAsync::Future<T> & /*out */)
-{
-    // noop
-}
-
-} // namespace Detail
-
-} // namespace KAsync
-
-//@endcond
-
-#endif // KASYNC_IMPL_H
diff --git a/src/executor_p.h b/src/executor_p.h
index 006e235..46d5879 100644
--- a/src/executor_p.h
+++ b/src/executor_p.h
@@ -1,321 +1,347 @@
 /*
  * Copyright 2014 - 2015 Daniel Vrátil <dvratil@redhat.com>
  * Copyright 2015 - 2019 Daniel Vrátil <dvratil@kde.org>
  * Copyright 2016  Christian Mollekopf <mollekopf@kolabsystems.com>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public License as
  * published by the Free Software Foundation; either version 2 of
  * the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library. If not, see <http://www.gnu.org/licenses/>.
  */
 
 #ifndef KASYNC_EXECUTOR_P_H
 #define KASYNC_EXECUTOR_P_H
 
-#include "async_impl.h"
 #include "execution_p.h"
 #include "continuations_p.h"
 #include "debug.h"
 
 namespace KAsync {
 
 template<typename T>
 class Future;
 
 template<typename T>
 class FutureWatcher;
 
 template<typename Out, typename ... In>
 class ContinuationHolder;
 
 template<typename Out, typename ... In>
 class Job;
 
 class Tracer;
 
 namespace Private {
 
 class ExecutorBase;
 using ExecutorBasePtr = QSharedPointer<ExecutorBase>;
 
 class ExecutorBase
 {
     template<typename Out, typename ... In>
     friend class Executor;
 
     template<typename Out, typename ... In>
     friend class KAsync::Job;
 
     friend struct Execution;
     friend class KAsync::Tracer;
 
 public:
     virtual ~ExecutorBase() = default;
 
     virtual ExecutionPtr exec(const ExecutorBasePtr &self, QSharedPointer<Private::ExecutionContext> context) = 0;
 
 protected:
     ExecutorBase(const ExecutorBasePtr &parent)
         : mPrev(parent)
     {}
 
     template<typename T>
     KAsync::Future<T>* createFuture(const ExecutionPtr &execution) const
     {
         return new KAsync::Future<T>(execution);
     }
 
     void prepend(const ExecutorBasePtr &e)
     {
         if (mPrev) {
             mPrev->prepend(e);
         } else {
             mPrev = e;
         }
     }
 
     void addToContext(const QVariant &entry)
     {
         mContext.push_back(entry);
     }
 
     void guard(const QObject *o)
     {
         mGuards.push_back(QPointer<const QObject>{o});
     }
 
     QString mExecutorName;
     QVector<QVariant> mContext;
     QVector<QPointer<const QObject>> mGuards;
     ExecutorBasePtr mPrev;
 };
 
 template<typename Out, typename ... In>
 class Executor : public ExecutorBase
 {
-    using PrevOut = typename detail::prevOut<In ...>::type;
+    using PrevOut = std::tuple_element_t<0, std::tuple<In ..., void>>;
 
 public:
     explicit Executor(ContinuationHolder<Out, In ...> &&workerHelper, const ExecutorBasePtr &parent = {},
                       ExecutionFlag executionFlag = ExecutionFlag::GoodCase)
         : ExecutorBase(parent)
         , mContinuationHolder(std::move(workerHelper))
         , executionFlag(executionFlag)
     {
         STORE_EXECUTOR_NAME("Executor", Out, In ...);
     }
 
     virtual ~Executor() = default;
 
     void run(const ExecutionPtr &execution)
     {
-        KAsync::Future<typename detail::prevOut<In ...>::type> *prevFuture = nullptr;
+        KAsync::Future<PrevOut> *prevFuture = nullptr;
         if (execution->prevExecution) {
-            prevFuture = execution->prevExecution->result<typename detail::prevOut<In ...>::type>();
+            prevFuture = execution->prevExecution->result<PrevOut>();
             assert(prevFuture->isFinished());
         }
 
         //Execute one of the available workers
         KAsync::Future<Out> *future = execution->result<Out>();
 
         const auto &continuation = Executor<Out, In ...>::mContinuationHolder;
         if (continuationIs<AsyncContinuation<Out, In ...>>(continuation)) {
             continuationGet<AsyncContinuation<Out, In ...>>(continuation)(std::forward<In>(prevFuture->value()) ..., *future);
         } else if (continuationIs<AsyncErrorContinuation<Out, In ...>>(continuation)) {
             continuationGet<AsyncErrorContinuation<Out, In ...>>(continuation)(
                     prevFuture->hasError() ? prevFuture->errors().first() : Error(),
                     std::forward<In>(prevFuture->value()) ..., *future);
         } else if (continuationIs<SyncContinuation<Out, In ...>>(continuation)) {
             callAndApply(std::forward<In>(prevFuture->value()) ...,
                          continuationGet<SyncContinuation<Out, In ...>>(continuation), *future, std::is_void<Out>());
             future->setFinished();
         } else if (continuationIs<SyncErrorContinuation<Out, In ...>>(continuation)) {
             assert(prevFuture);
             callAndApply(prevFuture->hasError() ? prevFuture->errors().first() : Error(),
                          std::forward<In>(prevFuture->value()) ...,
                          continuationGet<SyncErrorContinuation<Out, In ...>>(continuation), *future, std::is_void<Out>());
             future->setFinished();
         } else if (continuationIs<JobContinuation<Out, In ...>>(continuation)) {
             executeJobAndApply(std::forward<In>(prevFuture->value()) ...,
                                continuationGet<JobContinuation<Out, In ...>>(continuation), *future, std::is_void<Out>());
         } else if (continuationIs<JobErrorContinuation<Out, In ...>>(continuation)) {
             executeJobAndApply(prevFuture->hasError() ? prevFuture->errors().first() : Error(),
                                std::forward<In>(prevFuture->value()) ...,
                                continuationGet<JobErrorContinuation<Out, In ...>>(continuation), *future, std::is_void<Out>());
         }
 
     }
 
     ExecutionPtr exec(const ExecutorBasePtr &self, QSharedPointer<Private::ExecutionContext> context) override
     {
         /*
          * One executor per job, created with the construction of the Job object.
          * One execution per job per exec(), created only once exec() is called.
          *
          * The executors make up the linked list that makes up the complete execution chain.
          *
          * The execution then tracks the execution of each executor.
          */
 
         // Passing 'self' to execution ensures that the Executor chain remains
         // valid until the entire execution is finished
         ExecutionPtr execution = ExecutionPtr::create(self);
 #ifndef QT_NO_DEBUG
         execution->tracer = std::make_unique<Tracer>(execution.data()); // owned by execution
 #endif
 
         context->guards += mGuards;
 
         // chainup
         execution->prevExecution = mPrev ? mPrev->exec(mPrev, context) : ExecutionPtr();
 
         execution->resultBase = ExecutorBase::createFuture<Out>(execution);
         //We watch our own future to finish the execution once we're done
         auto fw = new KAsync::FutureWatcher<Out>();
         QObject::connect(fw, &KAsync::FutureWatcher<Out>::futureReady,
                          [fw, execution]() {
                              execution->setFinished();
                              delete fw;
                          });
         fw->setFuture(*execution->result<Out>());
 
         KAsync::Future<PrevOut> *prevFuture = execution->prevExecution ? execution->prevExecution->result<PrevOut>()
                                                                        : nullptr;
         if (!prevFuture || prevFuture->isFinished()) { //The previous job is already done
             runExecution(prevFuture, execution, context->guardIsBroken());
         } else { //The previous job is still running and we have to wait for it's completion
             auto prevFutureWatcher = new KAsync::FutureWatcher<PrevOut>();
             QObject::connect(prevFutureWatcher, &KAsync::FutureWatcher<PrevOut>::futureReady,
                              [prevFutureWatcher, execution, this, context]() {
                                  auto prevFuture = prevFutureWatcher->future();
                                  assert(prevFuture.isFinished());
                                  delete prevFutureWatcher;
                                  runExecution(&prevFuture, execution, context->guardIsBroken());
                              });
 
             prevFutureWatcher->setFuture(*static_cast<KAsync::Future<PrevOut>*>(prevFuture));
         }
 
         return execution;
     }
 
 private:
     void runExecution(KAsync::Future<PrevOut> *prevFuture, const ExecutionPtr &execution, bool guardIsBroken)
     {
         if (guardIsBroken) {
             execution->resultBase->setFinished();
             return;
         }
         if (prevFuture) {
             if (prevFuture->hasError() && executionFlag == ExecutionFlag::GoodCase) {
                 //Propagate the error to the outer Future
                 Q_ASSERT(prevFuture->errors().size() == 1);
                 execution->resultBase->setError(prevFuture->errors().first());
                 return;
             }
             if (!prevFuture->hasError() && executionFlag == ExecutionFlag::ErrorCase) {
                 //Propagate the value to the outer Future
-                KAsync::detail::copyFutureValue<PrevOut>(*prevFuture, *execution->result<PrevOut>());
+                copyFutureValue<PrevOut>(*prevFuture, *execution->result<PrevOut>());
                 execution->resultBase->setFinished();
                 return;
             }
         }
         run(execution);
     }
 
     void executeJobAndApply(In && ... input, const JobContinuation<Out, In ...> &func,
                             Future<Out> &future, std::false_type)
     {
         func(std::forward<In>(input) ...)
             .template then<void, Out>([&future](const KAsync::Error &error, Out &&v,
                                                 KAsync::Future<void> &f) {
                 if (error) {
                     future.setError(error);
                 } else {
                     future.setResult(std::move(v));
                 }
                 f.setFinished();
             }).exec();
     }
 
     void executeJobAndApply(In && ... input, const JobContinuation<Out, In ...> &func,
                             Future<Out> &future, std::true_type)
     {
         func(std::forward<In>(input) ...)
             .template then<void>([&future](const KAsync::Error &error, KAsync::Future<void> &f) {
                 if (error) {
                     future.setError(error);
                 } else {
                     future.setFinished();
                 }
                 f.setFinished();
             }).exec();
     }
 
     void executeJobAndApply(const Error &error, In && ... input, const JobErrorContinuation<Out, In ...> &func,
                             Future<Out> &future, std::false_type)
     {
         func(error, std::forward<In>(input) ...)
             .template then<void, Out>([&future](const KAsync::Error &error, Out &&v,
                                                 KAsync::Future<void> &f) {
                 if (error) {
                     future.setError(error);
                 } else {
                     future.setResult(std::move(v));
                 }
                 f.setFinished();
             }).exec();
     }
 
     void executeJobAndApply(const Error &error, In && ... input, const JobErrorContinuation<Out, In ...> &func,
                             Future<Out> &future, std::true_type)
     {
         func(error, std::forward<In>(input) ...)
             .template then<void>([&future](const KAsync::Error &error, KAsync::Future<void> &f) {
                 if (error) {
                     future.setError(error);
                 } else {
                     future.setFinished();
                 }
                 f.setFinished();
             }).exec();
     }
 
     void callAndApply(In && ... input, const SyncContinuation<Out, In ...> &func, Future<Out> &future, std::false_type)
     {
         future.setValue(func(std::forward<In>(input) ...));
     }
 
     void callAndApply(In && ... input, const SyncContinuation<Out, In ...> &func, Future<Out> &, std::true_type)
     {
         func(std::forward<In>(input) ...);
     }
 
     void callAndApply(const Error &error, In && ... input, const SyncErrorContinuation<Out, In ...> &func, Future<Out> &future, std::false_type)
     {
         future.setValue(func(error, std::forward<In>(input) ...));
     }
 
     void callAndApply(const Error &error, In && ... input, const SyncErrorContinuation<Out, In ...> &func, Future<Out> &, std::true_type)
     {
         func(error, std::forward<In>(input) ...);
     }
 
+
+    template<typename T,
+             class = std::enable_if_t<!std::is_void<T>::value>,
+             class = std::enable_if_t<std::is_move_constructible<T>::value>
+            >
+    void copyFutureValue(KAsync::Future<T> &in, KAsync::Future<T> &out)
+    {
+        out.setValue(std::move(in.value()));
+    }
+
+    template<typename T,
+             class = std::enable_if_t<!std::is_void<T>::value>,
+             class = std::enable_if_t<!std::is_move_constructible<T>::value>,
+             class = std::enable_if_t<std::is_copy_constructible<T>::value>
+            >
+    void copyFutureValue(const KAsync::Future<T> &in, KAsync::Future<T> &out)
+    {
+        out.setValue(in.value());
+    }
+
+    template<typename T,
+             class = std::enable_if_t<std::is_void<T>::value>
+            >
+    void copyFutureValue(const KAsync::Future<T> &, KAsync::Future<T> &)
+    {
+        //noop
+    }
 private:
     ContinuationHolder<Out, In ...> mContinuationHolder;
     const ExecutionFlag executionFlag;
 };
 
 } // namespace Private
 } // nameapce KAsync
 
 #endif
 
diff --git a/src/job_impl.h b/src/job_impl.h
index bf5cafe..515ff5c 100644
--- a/src/job_impl.h
+++ b/src/job_impl.h
@@ -1,342 +1,343 @@
 /*
  * Copyright 2014 - 2015 Daniel Vrátil <dvratil@redhat.com>
  * Copyright 2015 - 2016 Daniel Vrátil <dvratil@kde.org>
  * Copyright 2016  Christian Mollekopf <mollekopf@kolabsystems.com>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public License as
  * published by the Free Software Foundation; either version 2 of
  * the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library. If not, see <http://www.gnu.org/licenses/>.
  */
 
 #ifndef KASYNC_JOB_IMPL_H
 #define KASYNC_JOB_IMPL_H
 
 #include "async.h"
+#include "traits_p.h"
 
 #include <QTimer>
 
 //@cond PRIVATE
 
 namespace KAsync
 {
 
 template<typename Out, typename ... In>
 template<typename ... InOther>
 Job<Out, In ...>::operator std::conditional_t<std::is_void<OutType>::value, IncompleteType, Job<void>> ()
 {
     return thenImpl<void, InOther ...>({JobContinuation<void, InOther ...>([](InOther ...){ return KAsync::null<void>(); })}, {});
 }
 
 template<typename Out, typename ... In>
 template<typename OutOther, typename ... InOther>
 Job<OutOther, In ...> Job<Out, In ...>::thenImpl(Private::ContinuationHolder<OutOther, InOther ...> workHelper,
                                                  Private::ExecutionFlag execFlag) const
 {
     thenInvariants<InOther ...>();
     return Job<OutOther, In ...>(QSharedPointer<Private::Executor<OutOther, InOther ...>>::create(
                 std::forward<Private::ContinuationHolder<OutOther, InOther ...>>(workHelper), mExecutor, execFlag));
 }
 
 template<typename Out, typename ... In>
 template<typename OutOther, typename ... InOther>
 Job<OutOther, In ...> Job<Out, In ...>::then(const Job<OutOther, InOther ...> &job) const
 {
     thenInvariants<InOther ...>();
     auto executor = job.mExecutor;
     executor->prepend(mExecutor);
     return Job<OutOther, In ...>(executor);
 }
 
 template<typename Out, typename ... In>
 Job<Out, In ...> Job<Out, In ...>::onError(SyncErrorContinuation<void> &&errorFunc) const
 {
     return Job<Out, In...>(QSharedPointer<Private::Executor<Out, Out>>::create(
                 // Extra indirection to allow propagating the result of a previous future when no
                 // error occurs
                 Private::ContinuationHolder<Out, Out>([errorFunc = std::move(errorFunc)](const Error &error, const Out &val) {
                     errorFunc(error);
                     return val;
                 }), mExecutor, Private::ExecutionFlag::ErrorCase));
 }
 
 template<> // Specialize for void jobs
 inline Job<void> Job<void>::onError(SyncErrorContinuation<void> &&errorFunc) const
 {
     return Job<void>(QSharedPointer<Private::Executor<void>>::create(
                 Private::ContinuationHolder<void>(std::forward<SyncErrorContinuation<void>>(errorFunc)),
                 mExecutor, Private::ExecutionFlag::ErrorCase));
 }
 
 template<typename Out, typename ... In>
 template<typename FirstIn>
 KAsync::Future<Out> Job<Out, In ...>::exec(FirstIn in)
 {
     // Inject a fake sync executor that will return the initial value
     Private::ExecutorBasePtr first = mExecutor;
     while (first->mPrev) {
         first = first->mPrev;
     }
 
     first->mPrev = QSharedPointer<Private::Executor<FirstIn>>::create(
             Private::ContinuationHolder<FirstIn>([val = std::move(in)](Future<FirstIn> &future) {
                  future.setResult(val);
             }));
 
     auto result = exec();
     // Remove the injected executor
     first->mPrev.reset();
     return result;
 }
 
 template<typename Out, typename ... In>
 KAsync::Future<Out> Job<Out, In ...>::exec()
 {
     Private::ExecutionPtr execution = mExecutor->exec(mExecutor, Private::ExecutionContext::Ptr::create());
     KAsync::Future<Out> result = *execution->result<Out>();
 
     return result;
 }
 
 template<typename Out, typename ... In>
 Job<Out, In ...>::Job(Private::ExecutorBasePtr executor)
     : JobBase(executor)
 {}
 
 template<typename Out, typename ... In>
 Job<Out, In ...>::Job(JobContinuation<Out, In ...> &&func)
     : JobBase(new Private::Executor<Out, In ...>(std::forward<JobContinuation<Out, In ...>>(func), {}))
 {
     qWarning() << "Creating job job";
     static_assert(sizeof...(In) <= 1, "Only one or zero input parameters are allowed.");
 }
 
 template<typename Out, typename ... In>
 template<typename OutOther>
 void Job<Out, In ...>::eachInvariants() const
 {
-    static_assert(detail::isIterable<Out>::value,
+    static_assert(traits::isContainer<Out>::value,
                     "The 'Each' task can only be connected to a job that returns a list or an array.");
-    static_assert(std::is_void<OutOther>::value || detail::isIterable<OutOther>::value,
+    static_assert(std::is_void<OutOther>::value || traits::isContainer<OutOther>::value,
                     "The result type of 'Each' task must be void, a list or an array.");
 }
 
 template<typename Out, typename ... In>
 template<typename InOtherFirst, typename ... InOtherTail>
 void Job<Out, In ...>::thenInvariants() const
 {
     static_assert(!std::is_void<Out>::value && (std::is_convertible<Out, InOtherFirst>::value || std::is_base_of<Out, InOtherFirst>::value),
                     "The return type of previous task must be compatible with input type of this task");
 }
 
 template<typename Out, typename ... In>
 template<typename ... InOther>
 auto Job<Out, In ...>::thenInvariants() const -> std::enable_if_t<(sizeof...(InOther) == 0)>
 {
 }
 
 inline KAsync::Job<void> waitForCompletion(QVector<KAsync::Future<void>> &futures)
 {
     struct Context {
         void removeWatcher(KAsync::FutureWatcher<void> *w)
         {
             pending.erase(std::remove_if(pending.begin(), pending.end(), [w](const auto &watcher) {
                 return w == watcher.get();
             }));
         }
 
         std::vector<std::unique_ptr<KAsync::FutureWatcher<void>>> pending;
     };
 
     return start<Context *>([]() {
             return new Context();
         })
         .then<Context*, Context*>([futures](Context *context, KAsync::Future<Context *> &future) {
             for (KAsync::Future<void> subFuture : futures) {
                 if (subFuture.isFinished()) {
                     continue;
                 }
                 // FIXME bind lifetime all watcher to future (repectively the main job
                 auto watcher = std::make_unique<KAsync::FutureWatcher<void>>();
                 QObject::connect(watcher.get(), &KAsync::FutureWatcher<void>::futureReady,
                                  [&future, watcher = watcher.get(), context]() {
                                     context->removeWatcher(watcher);
                                     if (context->pending.empty()) {
                                         future.setResult(context);
                                     }
                                 });
                 watcher->setFuture(subFuture);
                 context->pending.push_back(std::move(watcher));
             }
             if (context->pending.empty()) {
                 future.setResult(context);
             }
         })
         .then<void, Context*>([](Context *context) {
             delete context;
         });
         // .finally<void>([context]() { delete context; });
 }
 
 template<typename List, typename ValueType>
 Job<void, List> forEach(KAsync::Job<void, ValueType> job)
 {
     auto cont = [job] (const List &values) mutable {
             auto error = QSharedPointer<KAsync::Error>::create();
             QVector<KAsync::Future<void>> list;
             for (const auto &v : values) {
                 auto future = job
                     .template then<void>([error] (const KAsync::Error &e) {
                         if (e && !*error) {
                             //TODO ideally we would aggregate the errors instead of just using the first one
                             *error = e;
                         }
                     })
                     .exec(v);
                 list.push_back(future);
             }
             return waitForCompletion(list)
                 .then<void>([error](KAsync::Future<void> &future) {
                     if (*error) {
                         future.setError(*error);
                     } else {
                         future.setFinished();
                     }
                 });
         };
     return Job<void, List>(QSharedPointer<Private::Executor<void, List>>::create(
                 Private::ContinuationHolder<void, List>(JobContinuation<void, List>(std::move(cont))), nullptr, Private::ExecutionFlag::GoodCase));
 }
 
 
 template<typename List, typename ValueType>
 Job<void, List> serialForEach(KAsync::Job<void, ValueType> job)
 {
     auto cont = [job] (const List &values) mutable {
             auto error = QSharedPointer<KAsync::Error>::create();
             auto serialJob = KAsync::null<void>();
             for (const auto &value : values) {
                 serialJob = serialJob.then<void>([value, job, error](KAsync::Future<void> &future) {
                     job.template then<void>([&future, error] (const KAsync::Error &e) {
                         if (e && !*error) {
                             //TODO ideally we would aggregate the errors instead of just using the first one
                             *error = e;
                         }
                         future.setFinished();
                     })
                     .exec(value);
                 });
             }
             return serialJob
                 .then<void>([error](KAsync::Future<void> &future) {
                     if (*error) {
                         future.setError(*error);
                     } else {
                         future.setFinished();
                     }
                 });
         };
     return Job<void, List>(QSharedPointer<Private::Executor<void, List>>::create(
             Private::ContinuationHolder<void, List>(JobContinuation<void, List>(std::move(cont))), nullptr, Private::ExecutionFlag::GoodCase));
 }
 
 template<typename List, typename ValueType>
 Job<void, List> forEach(JobContinuation<void, ValueType> &&func)
 {
     return forEach<List, ValueType>(KAsync::start<void, ValueType>(std::forward<JobContinuation<void, ValueType>>(func)));
 }
 
 template<typename List, typename ValueType>
 Job<void, List> serialForEach(JobContinuation<void, ValueType> &&func)
 {
     return serialForEach<List, ValueType>(KAsync::start<void, ValueType>(std::forward<JobContinuation<void, ValueType>>(func)));
 }
 
 template<typename Out>
 Job<Out> null()
 {
     return KAsync::start<Out>(
         [](KAsync::Future<Out> &future) {
             future.setFinished();
         });
 }
 
 template<typename Out>
 Job<Out> value(Out v)
 {
     return KAsync::start<Out>(
         [val = std::move(v)](KAsync::Future<Out> &future) {
             future.setResult(val);
         });
 }
 
 template<typename Out>
 Job<Out> error(int errorCode, const QString &errorMessage)
 {
     return error<Out>({errorCode, errorMessage});
 }
 
 template<typename Out>
 Job<Out> error(const char *message)
 {
     return error<Out>(Error(message));
 }
 
 template<typename Out>
 Job<Out> error(const Error &error)
 {
     return KAsync::start<Out>(
         [error](KAsync::Future<Out> &future) {
             future.setError(error);
         });
 }
 
 inline Job<void> doWhile(const Job<ControlFlowFlag> &body)
 {
     return KAsync::start<void>([body] (KAsync::Future<void> &future) {
         auto job = body.then<void, ControlFlowFlag>([&future, body](const KAsync::Error &error, ControlFlowFlag flag) {
             if (error) {
                 future.setError(error);
                 future.setFinished();
             } else if (flag == ControlFlowFlag::Continue) {
                 doWhile(body).then<void>([&future](const KAsync::Error &error) {
                     if (error) {
                         future.setError(error);
                     }
                     future.setFinished();
                 }).exec();
             } else {
                 future.setFinished();
             }
         }).exec();
     });
 }
 
 inline Job<void> doWhile(const JobContinuation<ControlFlowFlag> &body)
 {
     return doWhile(KAsync::start<ControlFlowFlag>([body] {
         return body();
     }));
 }
 
 inline Job<void> wait(int delay)
 {
     return KAsync::start<void>([delay](KAsync::Future<void> &future) {
         QTimer::singleShot(delay, [&future]() {
             future.setFinished();
         });
     });
 }
 } // namespace KAsync
 
 //@endcond
 
 #endif // KASYNC_JOB_IMPL_H
diff --git a/src/traits_p.h b/src/traits_p.h
new file mode 100644
index 0000000..8b76c38
--- /dev/null
+++ b/src/traits_p.h
@@ -0,0 +1,45 @@
+/*
+ * Copyright 2019 Daniel Vrátil <dvratil@kde.org>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Library General Public License as
+ * published by the Free Software Foundation; either version 2 of
+ * the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU Library General Public License for more details.
+ *
+ * You should have received a copy of the GNU Library General Public License
+ * along with this library. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef KASYNC_TRAITS_H_
+#define KASYNC_TRAITS_H_
+
+#include <utility>
+
+namespace KAsync {
+
+namespace traits {
+
+template<typename T, typename = void>
+struct isContainer {
+    enum { value = 0 };
+};
+
+template<typename T>
+struct isContainer<T, std::void_t<decltype(std::declval<T&>().begin()),
+                                  decltype(std::declval<T&>().end()),
+                                  typename T::value_type>>
+{
+    enum { value = 1 };
+};
+
+
+
+} // namespace traits
+} // namespace KAsync
+
+#endif