diff --git a/src/qtpromise/qpromise.h b/src/qtpromise/qpromise.h
index 47252f2..a69769a 100644
--- a/src/qtpromise/qpromise.h
+++ b/src/qtpromise/qpromise.h
@@ -23,6 +23,9 @@ public:
     template <typename F, typename std::enable_if<QtPromisePrivate::ArgsOf<F>::count != 1, int>::type = 0>
     inline QPromiseBase(F resolver);
 
+    template <typename U>
+    inline QPromiseBase(const QPromise<U>& other);
+
     QPromiseBase(const QPromiseBase<T>& other): m_d(other.m_d) {}
     QPromiseBase(const QPromise<T>& other): m_d(other.m_d) {}
     QPromiseBase(QPromiseBase<T>&& other) Q_DECL_NOEXCEPT { swap(other); }
@@ -94,6 +97,9 @@ public: // STATIC
     inline static QPromise<T> resolve(const T& value);
     inline static QPromise<T> resolve(T&& value);
 
+    template <typename U>
+    operator QPromise<U>();
+
 private:
     friend class QPromiseBase<T>;
 };
@@ -105,6 +111,9 @@ public:
     template <typename F>
     QPromise(F&& resolver): QPromiseBase<void>(std::forward<F>(resolver)) { }
 
+    template <typename T>
+    QPromise(const QPromise<T>& other);
+
 public: // STATIC
     template <template <typename, typename...> class Sequence = QVector, typename ...Args>
     inline static QPromise<void> all(const Sequence<QPromise<void>, Args...>& promises);
diff --git a/src/qtpromise/qpromise.inl b/src/qtpromise/qpromise.inl
index 5a3fb96..ed6fe45 100644
--- a/src/qtpromise/qpromise.inl
+++ b/src/qtpromise/qpromise.inl
@@ -74,6 +74,19 @@ inline QPromiseBase<T>::QPromiseBase(F callback)
     }
 }
 
+template <typename T>
+template <typename U>
+inline QPromiseBase<T>::QPromiseBase(const QPromise<U>& other)
+    : m_d(new QtPromisePrivate::PromiseData<T>())
+{
+    using namespace QtPromisePrivate;
+
+    QPromiseResolve<T> resolve(*this);
+    QPromiseReject<T> reject(*this);
+
+    PromiseFulfill<QPromise<U> >::call(other, PromiseCast<U, T>::apply(resolve), reject);
+}
+
 template <typename T>
 template <typename TFulfilled, typename TRejected>
 inline typename QtPromisePrivate::PromiseHandler<T, TFulfilled>::Promise
@@ -244,6 +257,21 @@ inline QPromise<T> QPromise<T>::resolve(T&& value)
     });
 }
 
+template <typename T>
+template <typename U>
+QPromise<T>::operator QPromise<U>()
+{
+    return QPromise<U>::resolve(U());
+}
+
+template <typename T>
+QPromise<void>::QPromise(const QPromise<T>& other)
+    : QPromiseBase<void>([&](const QPromiseResolve<void>& resolve, const QPromiseReject<void>& reject) {
+        QtPromisePrivate::PromiseFulfill<QPromise<T> >::call(other, resolve, reject);
+    })
+{
+}
+
 template <template <typename, typename...> class Sequence, typename ...Args>
 inline QPromise<void> QPromise<void>::all(const Sequence<QPromise<void>, Args...>& promises)
 {
diff --git a/src/qtpromise/qpromise_p.h b/src/qtpromise/qpromise_p.h
index 723a422..a267879 100644
--- a/src/qtpromise/qpromise_p.h
+++ b/src/qtpromise/qpromise_p.h
@@ -122,10 +122,8 @@ struct PromiseDeduce<QtPromise::QPromise<T>>
 template <typename T>
 struct PromiseFulfill
 {
-    static void call(
-        T&& value,
-        const QtPromise::QPromiseResolve<T>& resolve,
-        const QtPromise::QPromiseReject<T>&)
+    template <typename TResolve, typename TReject>
+    static void call(T&& value, const TResolve& resolve, const TReject&)
     {
         resolve(std::move(value));
     }
@@ -134,10 +132,11 @@ struct PromiseFulfill
 template <typename T>
 struct PromiseFulfill<QtPromise::QPromise<T>>
 {
+    template <typename TResolve, typename TReject>
     static void call(
         const QtPromise::QPromise<T>& promise,
-        const QtPromise::QPromiseResolve<T>& resolve,
-        const QtPromise::QPromiseReject<T>& reject)
+        const TResolve& resolve,
+        const TReject& reject)
     {
         if (promise.isFulfilled()) {
             resolve(promise.m_d->value());
@@ -156,9 +155,9 @@ struct PromiseFulfill<QtPromise::QPromise<T>>
 template <>
 struct PromiseFulfill<QtPromise::QPromise<void>>
 {
-    template <typename TPromise, typename TResolve, typename TReject>
+    template <typename TResolve, typename TReject>
     static void call(
-        const TPromise& promise,
+        const QtPromise::QPromise<void>& promise,
         const TResolve& resolve,
         const TReject& reject)
     {
@@ -397,6 +396,67 @@ struct PromiseCatcher<T, std::nullptr_t, void>
     }
 };
 
+template <typename T, typename U>
+struct PromiseCast
+{
+    template <typename F>
+    static auto apply(const F& resolve)
+    {
+        return [=](const QSharedPointer<T>& value) {
+            resolve(static_cast<T>(*value));
+        };
+    }
+};
+
+template <typename T>
+struct PromiseCast<T, void>
+{
+    template <typename F>
+    static auto apply(const F& resolve)
+    {
+        return [=](const QSharedPointer<T>&) {
+            resolve();
+        };
+    }
+};
+
+/*
+template <typename T>
+struct PromiseCast<T, QVariant>
+{
+    static QtPromise::QPromise<QVariant> cast(
+        const QtPromise::QPromiseBase<T>& input)
+    {
+        return input.then([](const T& res) {
+            return QVariant::fromValue(res);
+        });
+    }
+};
+
+template <typename U>
+struct PromiseCast<QVariant, U>
+{
+    static QtPromise::QPromise<U> cast(
+        const QtPromise::QPromiseBase<QVariant>& input)
+    {
+        return input.then([](const QVariant& res) {
+            return res.value<U>();
+        });
+    }
+};
+
+template <>
+struct PromiseCast<void, QVariant>
+{
+    static QtPromise::QPromise<void> cast(
+        const QtPromise::QPromiseBase<QVariant>& input)
+    {
+        return input.then([]() {
+        });
+    }
+};
+*/
+
 template <typename T> class PromiseData;
 
 template <typename T, typename F>
@@ -626,4 +686,4 @@ private:
 
 } // namespace QtPromise
 
-#endif // ifndef QTPROMISE_QPROMISE_H
+#endif // ifndef QTPROMISE_QPROMISE_P_H
diff --git a/tests/auto/qtpromise/qpromise/cast/cast.pro b/tests/auto/qtpromise/qpromise/cast/cast.pro
new file mode 100644
index 0000000..592b3f3
--- /dev/null
+++ b/tests/auto/qtpromise/qpromise/cast/cast.pro
@@ -0,0 +1,4 @@
+TARGET = tst_qpromise_cast
+SOURCES += $$PWD/tst_cast.cpp
+
+include(../../qtpromise.pri)
diff --git a/tests/auto/qtpromise/qpromise/cast/tst_cast.cpp b/tests/auto/qtpromise/qpromise/cast/tst_cast.cpp
new file mode 100644
index 0000000..03afc42
--- /dev/null
+++ b/tests/auto/qtpromise/qpromise/cast/tst_cast.cpp
@@ -0,0 +1,135 @@
+// Tests
+#include "../../shared/utils.h"
+
+// QtPromise
+#include <QtPromise>
+
+// Qt
+#include <QtTest>
+
+using namespace QtPromise;
+
+class tst_qpromise_cast : public QObject
+{
+    Q_OBJECT
+
+private Q_SLOTS:
+    void typeToVoid();
+
+
+    //void castToVoidOperator();
+    //void typeToVariant();   // QPromise<T>.cast<QVariant>()
+    //void variantToType();
+    //void voidToVariant();   // QPromise<void>.cast<QVariant>()
+    //void variantToVoid();
+
+    //void jsonValueToJsonObject();
+};
+
+QTEST_MAIN(tst_qpromise_cast)
+#include "tst_cast.moc"
+
+void tst_qpromise_cast::typeToVoid()
+{
+    QPromise<void> p0 = QPromise<int>::resolve(42);
+    QPromise<void> p1 = QPromise<QString>::resolve(QString("foo"));
+    QVERIFY(p0.isFulfilled());
+    QVERIFY(p1.isFulfilled());
+}
+
+//void tst_qpromise_cast::castToVoidOperator()
+//{
+    //auto p0 = QPromise<int>::resolve(42);
+    //QPromise<double> p1(p0);
+    //QPromise<void> p2(p0);
+    //auto p4 = QPromise<QString>::resolve("foo");
+    //
+    //p0.then([](int res) { qDebug() << res; });
+    //p1.then([](double res) { qDebug() << res; });
+    //p2.then([]() { qDebug() << "done"; });
+    //
+    //foo().then([]() {
+    //    qDebug() << "done";
+    //}).wait();
+    //
+    //QPromise<QVariant>::all({p0, p1, p4}).then([](const QVector<QVariant>& res) {
+    //    qDebug() << "all done!" << res;
+    //}).wait();
+//}
+
+/*
+namespace {
+
+template <typename T, typename U>
+void test_qpromise_cast(const T& t, const U& u)
+{
+    auto p = QPromise<T>::resolve(t).cast<U>();
+    Q_STATIC_ASSERT((std::is_same<decltype(p), QPromise<U> >::value));
+    QCOMPARE(waitForValue(p, U()), u);
+}
+
+template <typename U>
+void test_qpromise_cast(const U& u)
+{
+    auto p = QPromise<void>::resolve().cast<U>();
+    Q_STATIC_ASSERT((std::is_same<decltype(p), QPromise<U> >::value));
+    QCOMPARE(waitForValue(p, U()), u);
+}
+
+} // anonymous namespace
+
+
+void tst_qpromise_cast::typeToVariant()
+{
+    test_qpromise_cast(42, QVariant(42));
+    test_qpromise_cast(4.2, QVariant(4.2));
+    test_qpromise_cast(true, QVariant(true));
+    test_qpromise_cast(QString("foo"), QVariant(QString("foo")));
+    test_qpromise_cast(QUrl("http://x.y.z"), QVariant(QUrl("http://x.y.z")));
+    test_qpromise_cast(QSize(128, 256), QVariant(QSize(128, 256)));
+    test_qpromise_cast(QDate(2018, 1, 1), QVariant(QDate(2018, 1, 1)));
+    test_qpromise_cast(QJsonValue("foo"), QVariant(QJsonValue("foo")));
+    test_qpromise_cast(QStringList{"foo", "bar"}, QVariant(QStringList{"foo", "bar"}));
+    test_qpromise_cast(QList<QVariant>{"foo", 42}, QVariant(QList<QVariant>{"foo", 42}));
+    test_qpromise_cast(QMap<QString, QVariant>{{"foo", 42}}, QVariant(QVariantMap{{"foo", 42}}));
+}
+
+void tst_qpromise_cast::voidToVariant()
+{
+    test_qpromise_cast(QVariant());
+}
+
+void tst_qpromise_cast::variantToType()
+{
+    // invalid
+    // int
+    // QString
+    // QColor
+    // QList
+}
+
+
+/*
+void tst_qpromise_cast::jsonValueToJsonObject()
+{
+    {   // QJsonValue(Null) -> QJsonObject
+        auto p = QPromise<QJsonValue>::resolve(QJsonValue()).cast<QJsonObject>();
+        Q_STATIC_ASSERT((std::is_same<decltype(p), QPromise<QJsonObject> >::value));
+        const QJsonObject res = waitForValue(p, QJsonObject());
+        QVERIFY(res.isEmpty());
+    }
+    {   // QJsonValue(int) -> QJsonObject
+        auto p = QPromise<QJsonValue>::resolve(QJsonValue(42)).cast<QJsonObject>();
+        Q_STATIC_ASSERT((std::is_same<decltype(p), QPromise<QJsonObject> >::value));
+        const QJsonObject res = waitForValue(p, QJsonObject());
+        QVERIFY(res.isEmpty());
+    }
+    {   // QJsonValue(QJsonObject) -> QJsonObject
+        const QJsonObject object{{"magic", 42}};
+        auto p = QPromise<QJsonValue>::resolve(QJsonValue(object)).cast<QJsonObject>();
+        Q_STATIC_ASSERT((std::is_same<decltype(p), QPromise<QJsonObject> >::value));
+        const QJsonObject res = waitForValue(p, QJsonObject());
+        QCOMPARE(res.value("magic"), 42);
+    }
+}
+*/
diff --git a/tests/auto/qtpromise/qpromise/qpromise.pro b/tests/auto/qtpromise/qpromise/qpromise.pro
index 814ad7d..0d47ba6 100644
--- a/tests/auto/qtpromise/qpromise/qpromise.pro
+++ b/tests/auto/qtpromise/qpromise/qpromise.pro
@@ -1,6 +1,7 @@
 TEMPLATE = subdirs
 SUBDIRS += \
     all \
+    cast \
     construct \
     delay \
     fail \