diff --git a/UnitTest/CMakeLists.txt b/UnitTest/CMakeLists.txt
index 83cf9f3..ab6864d 100644
--- a/UnitTest/CMakeLists.txt
+++ b/UnitTest/CMakeLists.txt
@@ -37,7 +37,7 @@ add_executable(UnitTest main.cpp
 )
 
 target_compile_definitions(UnitTest
-    PUBLIC LOG_FILTER_LEVEL=1
+    PUBLIC LOG_FILTER_LEVEL=2
 )
 
 target_link_libraries(UnitTest
diff --git a/UnitTest/Universal/PromiseTest.cpp b/UnitTest/Universal/PromiseTest.cpp
index 803e35c..b1994d2 100644
--- a/UnitTest/Universal/PromiseTest.cpp
+++ b/UnitTest/Universal/PromiseTest.cpp
@@ -1,9 +1,109 @@
-#include "Promise.h"
+#include "BoostLog.h"
+#include "IoContext.h"
+#include <boost/asio/defer.hpp>
+#include <boost/asio/io_context.hpp>
+#include <boost/asio/strand.hpp>
 #include <boost/test/unit_test.hpp>
 #include <sstream>
 #include <variant>
 #include <vector>
 
+#include "Promise.h" // 在这之前 #include "IoContext.h" 以支持 delay
+
+BOOST_AUTO_TEST_SUITE(PromiseTestCase)
+
+class PromiseContext {
+public:
+    PromiseContext() : m_ioContext(std::thread::hardware_concurrency()), m_guarder(m_ioContext.get_executor()) {
+    }
+
+    ~PromiseContext() {
+        m_guarder.reset();
+        for (auto &thread : m_threads) {
+            thread.join();
+        }
+    }
+
+    void start() {
+        if (m_threads.empty()) {
+            auto threads = std::thread::hardware_concurrency();
+            for (int i = 0; i < threads; i++) {
+                m_threads.emplace_back([this]() { m_ioContext.run(); });
+            }
+        }
+    }
+
+    void setValue(float value) {
+        if (m_value != value) {
+            m_value = value;
+        }
+    }
+    inline static const float kRes = 0.42f;
+    float functionNoArg() const {
+        return m_value;
+    }
+    float functionArgByVal(float v) const {
+        return v + m_value;
+    }
+    float functionArgByRef(const float &v) const {
+        return v + m_value;
+    }
+
+    static float kFnNoArg() {
+        return kRes;
+    }
+    static float kFnArgByVal(float v) {
+        return v;
+    }
+    static float kFnArgByRef(const float &v) {
+        return v;
+    }
+
+    static float stringToFloatNoArg() {
+        return std::stof(kErr);
+    }
+    static float stringToFloatArgByVal(std::string e) {
+        return std::stof(e);
+    }
+    static float stringToFloatArgByRef(const std::string &e) {
+        return std::stof(e);
+    }
+
+    enum class Enum1 { Value0, Value1, Value2 };
+    enum class Enum2 { Value0, Value1, Value2 };
+    struct Foo {
+        Foo() = default;
+        Foo(int foo) : m_foo{foo} {
+        }
+
+        bool operator==(const Foo &rhs) const {
+            return m_foo == rhs.m_foo;
+        }
+
+        int m_foo{-1};
+    };
+    struct Bar {
+        Bar() = default;
+        Bar(const Foo &other) : m_bar{other.m_foo} {
+        }
+
+        bool operator==(const Bar &rhs) const {
+            return m_bar == rhs.m_bar;
+        }
+
+        int m_bar{-1};
+    };
+
+protected:
+    boost::asio::io_context m_ioContext;
+    boost::asio::executor_work_guard<boost::asio::io_context::executor_type> m_guarder;
+
+    std::vector<std::thread> m_threads;
+    float m_value = 249.f;
+
+    inline static const std::string kErr{"0.42"};
+};
+
 template <typename T>
 static inline T waitForValue(const Promise<T> &promise, const T &initial) {
     T value(initial);
@@ -18,6 +118,616 @@ static inline T waitForValue(const Promise<void> &promise, const T &initial, con
     return value;
 }
 
+template <typename T, typename E>
+static inline E waitForError(const Promise<T> &promise, const E &initial) {
+    E error(initial);
+    promise
+        .fail([&](const E &err) {
+            error = err;
+            return T();
+        })
+        .wait();
+    return error;
+}
+
+template <typename E>
+static inline E waitForError(const Promise<void> &promise, const E &initial) {
+    E error(initial);
+    promise.fail([&](const E &err) { error = err; }).wait();
+    return error;
+}
+
+template <typename E, typename T>
+static inline bool waitForRejected(const T &promise) {
+    bool result = false;
+    promise.tapFail([&](const E &) { result = true; }).wait();
+    return result;
+}
+
+BOOST_AUTO_TEST_CASE(ConstructResolveSyncOneArg) {
+    Promise<int> p{[](const PromiseResolve<int> &resolve) { resolve(42); }};
+
+    BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{});
+    BOOST_CHECK_EQUAL(waitForValue(p, -1), 42);
+}
+
+BOOST_AUTO_TEST_CASE(ConstructResolveSyncOneArgVoid) {
+    Promise<void> p{[](const PromiseResolve<void> &resolve) { resolve(); }};
+
+    BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{});
+    BOOST_CHECK_EQUAL(waitForValue(p, -1, 42), 42);
+}
+
+BOOST_AUTO_TEST_CASE(ConstructResolveSyncTwoArgs) {
+    Promise<int> p{[](const PromiseResolve<int> &resolve, const PromiseReject<int> &) { resolve(42); }};
+
+    BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{});
+    BOOST_CHECK_EQUAL(waitForValue(p, -1), 42);
+}
+
+BOOST_AUTO_TEST_CASE(ConstructResolveSyncTwoArgsVoid) {
+    Promise<void> p{[](const PromiseResolve<void> &resolve, const PromiseReject<void> &) { resolve(); }};
+
+    BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{});
+    BOOST_CHECK_EQUAL(waitForValue(p, -1, 42), 42);
+}
+
+BOOST_FIXTURE_TEST_CASE(ConstructResolveAsyncOneArg, PromiseContext) {
+    auto id = std::this_thread::get_id();
+    Promise<int> p{[this, &id](const PromiseResolve<int> &resolve) {
+        boost::asio::defer(m_ioContext, [&id, resolve]() {
+            resolve(42);
+            id = std::this_thread::get_id();
+        });
+    }};
+    BOOST_CHECK_EQUAL(p.isPending(), true);
+    start();
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{});
+    BOOST_CHECK_EQUAL(waitForValue(p, -1), 42);
+    BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    BOOST_CHECK_NE(id, std::this_thread::get_id());
+}
+
+BOOST_FIXTURE_TEST_CASE(ConstructResolveAsyncOneArgVoid, PromiseContext) {
+    auto id = std::this_thread::get_id();
+    Promise<void> p{[&id, this](const PromiseResolve<void> &resolve) {
+        boost::asio::defer(m_ioContext, [&id, resolve]() {
+            resolve();
+            id = std::this_thread::get_id();
+        });
+    }};
+    BOOST_CHECK_EQUAL(p.isPending(), true);
+    start();
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{});
+    BOOST_CHECK_EQUAL(waitForValue(p, -1, 42), 42);
+    BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    BOOST_CHECK_NE(id, std::this_thread::get_id());
+}
+
+BOOST_FIXTURE_TEST_CASE(ConstructResolveAsyncTwoArgs, PromiseContext) {
+    auto id = std::this_thread::get_id();
+    Promise<int> p{[&id, this](const PromiseResolve<int> &resolve, const PromiseReject<int> &) {
+        boost::asio::defer(m_ioContext, [&id, resolve]() {
+            resolve(42);
+            id = std::this_thread::get_id();
+        });
+    }};
+
+    BOOST_CHECK_EQUAL(p.isPending(), true);
+    start();
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{});
+    BOOST_CHECK_EQUAL(waitForValue(p, -1), 42);
+    BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    BOOST_CHECK_NE(id, std::this_thread::get_id());
+}
+
+BOOST_FIXTURE_TEST_CASE(ConstructResolveAsyncTwoArgsVoid, PromiseContext) {
+    auto id = std::this_thread::get_id();
+    Promise<void> p{[&id, this](const PromiseResolve<void> &resolve, const PromiseReject<void> &) {
+        boost::asio::defer(m_ioContext, [&id, resolve]() {
+            resolve();
+            id = std::this_thread::get_id();
+        });
+    }};
+
+    BOOST_CHECK_EQUAL(p.isPending(), true);
+    start();
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{});
+    BOOST_CHECK_EQUAL(waitForValue(p, -1, 42), 42);
+    BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    BOOST_CHECK_NE(id, std::this_thread::get_id());
+}
+
+BOOST_AUTO_TEST_CASE(ConstructRejectSync) {
+    Promise<int> p{[](const PromiseResolve<int> &, const PromiseReject<int> &reject) { reject(std::string{"foo"}); }};
+
+    BOOST_CHECK_EQUAL(p.isRejected(), true);
+    BOOST_CHECK_EQUAL(waitForValue(p, -1), -1);
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{"foo"});
+}
+
+BOOST_AUTO_TEST_CASE(ConstructRejectSyncVoid) {
+    Promise<void> p{[](const PromiseResolve<void> &, const PromiseReject<void> &reject) { reject(std::string{"foo"}); }};
+
+    BOOST_CHECK_EQUAL(p.isRejected(), true);
+    BOOST_CHECK_EQUAL(waitForValue(p, -1, 42), -1);
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{"foo"});
+}
+
+BOOST_FIXTURE_TEST_CASE(ConstructRejectAsync, PromiseContext) {
+    auto id = std::this_thread::get_id();
+    Promise<int> p{[this, &id](const PromiseResolve<int> &, const PromiseReject<int> &reject) {
+        boost::asio::defer(m_ioContext, [&id, reject]() {
+            reject(std::string{"foo"});
+            id = std::this_thread::get_id();
+        });
+    }};
+
+    BOOST_CHECK_EQUAL(p.isPending(), true);
+    start();
+    BOOST_CHECK_EQUAL(waitForValue(p, -1), -1);
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{"foo"});
+    BOOST_CHECK_EQUAL(p.isRejected(), true);
+    BOOST_CHECK_NE(id, std::this_thread::get_id());
+}
+
+BOOST_FIXTURE_TEST_CASE(ConstructRejectAsyncVoid, PromiseContext) {
+    auto id = std::this_thread::get_id();
+    Promise<void> p{[this, &id](const PromiseResolve<void> &, const PromiseReject<void> &reject) {
+        boost::asio::defer(m_ioContext, [&id, reject]() {
+            reject(std::string{"foo"});
+            id = std::this_thread::get_id();
+        });
+    }};
+
+    BOOST_CHECK_EQUAL(p.isPending(), true);
+    start();
+    BOOST_CHECK_EQUAL(waitForValue(p, -1, 42), -1);
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{"foo"});
+    BOOST_CHECK_EQUAL(p.isRejected(), true);
+    BOOST_CHECK_NE(id, std::this_thread::get_id());
+}
+
+BOOST_AUTO_TEST_CASE(ConstructRejectThrowOneArg) {
+    Promise<int> p{[](const PromiseResolve<int> &) { throw std::string{"foo"}; }};
+
+    BOOST_CHECK_EQUAL(p.isRejected(), true);
+    BOOST_CHECK_EQUAL(waitForValue(p, -1), -1);
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{"foo"});
+}
+
+BOOST_AUTO_TEST_CASE(ConstructRejectThrowOneArgVoid) {
+    Promise<void> p{[](const PromiseResolve<void> &) { throw std::string{"foo"}; }};
+
+    BOOST_CHECK_EQUAL(p.isRejected(), true);
+    BOOST_CHECK_EQUAL(waitForValue(p, -1, 42), -1);
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{"foo"});
+}
+
+BOOST_AUTO_TEST_CASE(ConstructRejectThrowTwoArgs) {
+    Promise<int> p{[](const PromiseResolve<int> &, const PromiseReject<int> &) { throw std::string{"foo"}; }};
+
+    BOOST_CHECK_EQUAL(p.isRejected(), true);
+    BOOST_CHECK_EQUAL(waitForValue(p, -1), -1);
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{"foo"});
+}
+
+BOOST_AUTO_TEST_CASE(ConstructRejectThrowTwoArgsVoid) {
+    Promise<void> p{[](const PromiseResolve<void> &, const PromiseReject<void> &) { throw std::string{"foo"}; }};
+
+    BOOST_CHECK_EQUAL(p.isRejected(), true);
+    BOOST_CHECK_EQUAL(waitForValue(p, -1, 42), -1);
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{"foo"});
+}
+
+BOOST_FIXTURE_TEST_CASE(ConstructRejectUndefined, PromiseContext) {
+    auto id = std::this_thread::get_id();
+    Promise<int> p{[this, &id](const PromiseResolve<int> &, const PromiseReject<int> &reject) {
+        boost::asio::defer(m_ioContext, [&id, reject]() {
+            reject();
+            id = std::this_thread::get_id();
+        });
+    }};
+    BOOST_CHECK_EQUAL(p.isPending(), true);
+    start();
+    BOOST_CHECK_EQUAL(waitForRejected<PromiseUndefinedException>(p), true);
+    BOOST_CHECK_NE(id, std::this_thread::get_id());
+}
+
+BOOST_FIXTURE_TEST_CASE(ConstructRejectUndefinedVoid, PromiseContext) {
+    auto id = std::this_thread::get_id();
+    Promise<void> p{[this, &id](const PromiseResolve<void> &, const PromiseReject<void> &reject) {
+        boost::asio::defer(m_ioContext, [&id, reject]() {
+            reject();
+            id = std::this_thread::get_id();
+        });
+    }};
+
+    BOOST_CHECK_EQUAL(p.isPending(), true);
+    start();
+    BOOST_CHECK_EQUAL(waitForRejected<PromiseUndefinedException>(p), true);
+    BOOST_CHECK_NE(id, std::this_thread::get_id());
+}
+
+BOOST_FIXTURE_TEST_CASE(ConvertFulfillTAsU, PromiseContext) {
+    // Static cast between primitive types.
+    {
+        auto p = Promise<float>::resolve(42.13).convert<int>();
+
+        static_assert((std::is_same<decltype(p), Promise<int>>::value));
+
+        BOOST_CHECK_EQUAL(waitForValue(p, -1), 42);
+        BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    }
+
+    // Convert enum class to int.
+    {
+        auto p = Promise<Enum1>::resolve(Enum1::Value1).convert<int>();
+
+        static_assert((std::is_same<decltype(p), Promise<int>>::value));
+
+        BOOST_CHECK_EQUAL(waitForValue(p, -1), 1);
+        BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    }
+
+    // Convert int to enum class.
+    {
+        auto p = Promise<int>::resolve(1).convert<Enum1>();
+
+        static_assert((std::is_same<decltype(p), Promise<Enum1>>::value));
+
+        BOOST_TEST((waitForValue(p, Enum1::Value0) == Enum1::Value1));
+        BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    }
+
+    // Convert between enums
+    {
+        auto p = Promise<Enum1>::resolve(Enum1::Value1).convert<Enum2>();
+
+        static_assert((std::is_same<decltype(p), Promise<Enum2>>::value));
+
+        BOOST_TEST((waitForValue(p, Enum2::Value0) == Enum2::Value1));
+        BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    }
+
+    // Converting constructor for non-Qt types.
+    // https://en.cppreference.com/w/cpp/language/converting_constructor
+    {
+        auto p = Promise<Foo>::resolve(Foo{42}).convert<Bar>();
+
+        static_assert((std::is_same<decltype(p), Promise<Bar>>::value));
+
+        BOOST_TEST((waitForValue(p, Bar{}) == Bar{42}));
+        BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    }
+
+    {
+        auto p = Promise<int>::resolve(42).convert<std::any>();
+
+        static_assert((std::is_same<decltype(p), Promise<std::any>>::value));
+        BOOST_CHECK_EQUAL(std::any_cast<int>(waitForValue(p, std::any{})), 42);
+        BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    }
+
+    {
+        using Variant = std::variant<int, Foo>;
+        auto p = Promise<Foo>::resolve(Foo{42}).convert<Variant>();
+
+        static_assert((std::is_same<decltype(p), Promise<Variant>>::value));
+
+        BOOST_TEST((std::get<Foo>(waitForValue(p, Variant{})) == Foo{42}));
+        BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+    }
+}
+
+BOOST_AUTO_TEST_CASE(ConvertFulfillTAsVoid) {
+    auto p = Promise<int>::resolve(42).convert<void>();
+
+    static_assert((std::is_same<decltype(p), Promise<void>>::value));
+
+    BOOST_CHECK_EQUAL(waitForValue(p, -1, 42), 42);
+    BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+}
+
+BOOST_AUTO_TEST_CASE(ConvertRejectUnconvertibleTypes) {
+    // A string incompatible with int due to its value.
+    {
+        auto p = Promise<std::string>::resolve(std::string{"42foo"}).convert<int>();
+
+        static_assert((std::is_same<decltype(p), Promise<int>>::value));
+
+        BOOST_TEST(waitForRejected<PromiseConversionException>(p));
+    }
+
+    // A standard library type unconvertible to a primitive type because there is no converter.
+    {
+        auto p = Promise<std::vector<int>>::resolve(std::vector<int>{42, -42}).convert<int>();
+
+        static_assert((std::is_same<decltype(p), Promise<int>>::value));
+
+        BOOST_TEST(waitForRejected<PromiseConversionException>(p));
+    }
+}
+
+BOOST_FIXTURE_TEST_CASE(DelayFulfilled, PromiseContext) {
+    using namespace std::chrono;
+    auto begin = system_clock::now();
+    int64_t elapsed = -1;
+    auto p = Promise<int>::resolve(42).delay(m_ioContext, 1000).finally([&]() {
+        elapsed = duration_cast<milliseconds>(system_clock::now() - begin).count();
+    });
+    start();
+    BOOST_CHECK_EQUAL(waitForValue(p, -1), 42);
+    BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+
+    BOOST_TEST(elapsed >= static_cast<int64_t>(1000 * 0.94));
+    BOOST_TEST(elapsed <= static_cast<int64_t>(1000 * 1.06));
+}
+
+BOOST_FIXTURE_TEST_CASE(DelayRejected, PromiseContext) {
+    using namespace std::chrono;
+    int64_t elapsed = -1;
+    auto begin = system_clock::now();
+
+    auto p = Promise<int>::reject(std::string{"foo"}).delay(m_ioContext, 1000).finally([&]() {
+        elapsed = duration_cast<milliseconds>(system_clock::now() - begin).count();
+    });
+    start();
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{"foo"});
+    BOOST_CHECK_EQUAL(p.isRejected(), true);
+    BOOST_TEST(elapsed <= 10);
+}
+
+BOOST_FIXTURE_TEST_CASE(DelayFulfilledStdChrono, PromiseContext) {
+    using namespace std::chrono;
+    int64_t elapsed = -1;
+
+    auto begin = system_clock::now();
+
+    auto p = Promise<int>::resolve(42).delay(m_ioContext, std::chrono::seconds{1}).finally([&]() {
+        elapsed = duration_cast<milliseconds>(system_clock::now() - begin).count();
+    });
+    start();
+    BOOST_CHECK_EQUAL(waitForValue(p, -1), 42);
+    BOOST_CHECK_EQUAL(p.isFulfilled(), true);
+
+    BOOST_TEST(elapsed >= static_cast<int64_t>(1000 * 0.94));
+    BOOST_TEST(elapsed <= static_cast<int64_t>(1000 * 1.06));
+}
+
+BOOST_FIXTURE_TEST_CASE(DelayRejectedStdChrono, PromiseContext) {
+    using namespace std::chrono;
+    int64_t elapsed = -1;
+
+    auto begin = system_clock::now();
+
+    auto p = Promise<int>::reject(std::string{"foo"}).delay(m_ioContext, std::chrono::seconds{1}).finally([&]() {
+        elapsed = duration_cast<milliseconds>(system_clock::now() - begin).count();
+    });
+    start();
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{"foo"});
+    BOOST_CHECK_EQUAL(p.isRejected(), true);
+    BOOST_TEST(elapsed <= 10);
+}
+
+BOOST_AUTO_TEST_CASE(EachEmptySequence) {
+    std::vector<int> values;
+    auto p = Promise<std::vector<int>>::resolve({}).each([&](int v, ...) { values.push_back(v); });
+
+    static_assert((std::is_same<decltype(p), Promise<std::vector<int>>>::value));
+    BOOST_CHECK_EQUAL(waitForValue(p, std::vector<int>{}), std::vector<int>{});
+    BOOST_CHECK_EQUAL(values, (std::vector<int>{}));
+}
+
+BOOST_AUTO_TEST_CASE(EachPreserveValues) {
+    std::vector<int> values;
+    auto p = Promise<std::vector<int>>::resolve({42, 43, 44}).each([&](int v, ...) { values.push_back(v + 1); });
+
+    static_assert((std::is_same<decltype(p), Promise<std::vector<int>>>::value));
+    BOOST_CHECK_EQUAL(waitForValue(p, std::vector<int>{}), (std::vector<int>{42, 43, 44}));
+    BOOST_CHECK_EQUAL(values, (std::vector<int>{43, 44, 45}));
+}
+
+BOOST_AUTO_TEST_CASE(EachIgnoreResult) {
+    std::vector<int> values;
+    auto p = Promise<std::vector<int>>::resolve({42, 43, 44}).each([&](int v, ...) {
+        values.push_back(v + 1);
+        return "Foo";
+    });
+
+    static_assert((std::is_same<decltype(p), Promise<std::vector<int>>>::value));
+    BOOST_CHECK_EQUAL(waitForValue(p, std::vector<int>{}), (std::vector<int>{42, 43, 44}));
+    BOOST_CHECK_EQUAL(values, (std::vector<int>{43, 44, 45}));
+}
+
+BOOST_FIXTURE_TEST_CASE(EachDelayedFulfilled, PromiseContext) {
+    auto strand = boost::asio::make_strand(m_ioContext);
+    std::map<int, int> values;
+    auto p = Promise<std::vector<int>>::resolve({42, 43, 44}).each([&](int v, int index) {
+        return Promise<void>::resolve().delay(strand, 50).then([&values, v, index]() {
+            values[v] = index;
+            return 42;
+        });
+    });
+    start();
+    static_assert((std::is_same<decltype(p), Promise<std::vector<int>>>::value));
+    BOOST_CHECK_EQUAL(waitForValue(p, std::vector<int>{}), (std::vector<int>{42, 43, 44}));
+    std::map<int, int> expected{{42, 0}, {43, 1}, {44, 2}};
+    BOOST_CHECK_EQUAL(values, expected);
+}
+
+BOOST_FIXTURE_TEST_CASE(EachDelayedRejected, PromiseContext) {
+    auto id = std::this_thread::get_id();
+    auto p = Promise<std::vector<int>>::resolve({42, 43, 44}).each([&id, this](int v, ...) {
+        return Promise<int>{[&, this](const PromiseResolve<int> &resolve, const PromiseReject<int> &reject) {
+            boost::asio::defer(m_ioContext, [&id, v, reject, resolve]() {
+                if (v == 44) {
+                    reject(std::string{"foo"});
+                } else {
+                    resolve(v);
+                }
+                id = std::this_thread::get_id();
+            });
+        }};
+    });
+    start();
+    static_assert((std::is_same<decltype(p), Promise<std::vector<int>>>::value));
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{"foo"});
+    BOOST_CHECK_NE(id, std::this_thread::get_id());
+}
+
+BOOST_FIXTURE_TEST_CASE(EachFunctorThrows, PromiseContext) {
+    auto p = Promise<std::vector<int>>::resolve({42, 43, 44}).each([](int v, ...) {
+        if (v == 44) {
+            throw std::string{"foo"};
+        }
+    });
+
+    static_assert((std::is_same<decltype(p), Promise<std::vector<int>>>::value));
+    BOOST_CHECK_EQUAL(waitForError(p, std::string{}), std::string{"foo"});
+}
+
+BOOST_FIXTURE_TEST_CASE(EachFunctorArguments, PromiseContext) {
+    std::vector<int> values;
+    auto p = Promise<std::vector<int>>::resolve({42, 43, 44}).each([&](int v, int i) {
+        values.push_back(i);
+        values.push_back(v);
+    });
+    static_assert((std::is_same<decltype(p), Promise<std::vector<int>>>::value));
+    BOOST_CHECK_EQUAL(waitForValue(p, std::vector<int>{}), (std::vector<int>{42, 43, 44}));
+    BOOST_CHECK_EQUAL(values, (std::vector<int>{0, 42, 1, 43, 2, 44}));
+}
+
+template <class Sequence>
+struct SequenceTester {
+    static void exec() {
+        std::vector<int> values;
+        auto p = PromiseHelper::resolve(Sequence{42, 43, 44})
+                     .each([&](int v, int i) {
+                         values.push_back(i);
+                         values.push_back(v);
+                     })
+                     .each([&](int v, ...) {
+                         values.push_back(v);
+                         return std::string{"foo"};
+                     })
+                     .each([&](int v, ...) {
+                         values.push_back(v + 1);
+                         return PromiseHelper::resolve(std::string{"foo"}).then([&]() { values.push_back(-1); });
+                     })
+                     .each([&](int v, ...) { values.push_back(v + 2); });
+
+        static_assert((std::is_same<decltype(p), Promise<Sequence>>::value));
+        BOOST_CHECK_EQUAL(waitForValue(p, Sequence{}), (Sequence{42, 43, 44}));
+
+        std::vector<int> expected{0, 42, 1, 43, 2, 44, 42, 43, 44, 43, -1, 44, -1, 45, -1, 44, 45, 46};
+        BOOST_CHECK_EQUAL(values, expected);
+    }
+};
+
+BOOST_AUTO_TEST_CASE(EachSequenceTypes) {
+    SequenceTester<std::list<int>>::exec();
+    SequenceTester<std::vector<int>>::exec();
+}
+
+BOOST_AUTO_TEST_CASE(FailSameType) {
+    // http://en.cppreference.com/w/cpp/error/exception
+    auto p = Promise<int>::reject(std::out_of_range("foo"));
+
+    std::string error;
+    p.fail([&](const std::domain_error &e) {
+         error += std::string{e.what()} + "0";
+         return -1;
+     })
+        .fail([&](const std::out_of_range &e) {
+            error += std::string{e.what()} + "1";
+            return -1;
+        })
+        .fail([&](const std::exception &e) {
+            error += std::string{e.what()} + "2";
+            return -1;
+        })
+        .wait();
+    BOOST_CHECK_EQUAL(error, std::string{"foo1"});
+}
+
+BOOST_AUTO_TEST_CASE(FailBaseClass) {
+    // http://en.cppreference.com/w/cpp/error/exception
+    auto p = Promise<int>::reject(std::out_of_range("foo"));
+
+    std::string error;
+    p.fail([&](const std::runtime_error &e) {
+         error += std::string{e.what()} + "0";
+         return -1;
+     })
+        .fail([&](const std::logic_error &e) {
+            error += std::string{e.what()} + "1";
+            return -1;
+        })
+        .fail([&](const std::exception &e) {
+            error += std::string{e.what()} + "2";
+            return -1;
+        })
+        .wait();
+    BOOST_CHECK_EQUAL(error, std::string{"foo1"});
+}
+
+BOOST_AUTO_TEST_CASE(FailCatchAll) {
+    auto p = Promise<int>::reject(std::out_of_range("foo"));
+    std::string error;
+    p.fail([&](const std::runtime_error &e) {
+         error += std::string{e.what()} + "0";
+         return -1;
+     })
+        .fail([&]() {
+            error += "bar";
+            return -1;
+        })
+        .fail([&](const std::exception &e) {
+            error += std::string{e.what()} + "2";
+            return -1;
+        })
+        .wait();
+    BOOST_CHECK_EQUAL(error, std::string{"bar"});
+}
+
+const std::string kErr{"0.42"};
+float stringToFloatNoArg() {
+    return std::stof(kErr);
+}
+float stringToFloatArgByVal(std::string e) {
+    return std::stof(e);
+}
+float stringToFloatArgByRef(const std::string &e) {
+    return std::stof(e);
+}
+
+const float kFail = -1.f;
+BOOST_FIXTURE_TEST_CASE(FailFunctionPtrHandlers, PromiseContext) {
+    { // Global functions.
+        auto p0 = Promise<float>::reject(kErr).fail(&stringToFloatNoArg);
+        auto p1 = Promise<float>::reject(kErr).fail(&stringToFloatArgByVal);
+        auto p2 = Promise<float>::reject(kErr).fail(&stringToFloatArgByRef);
+
+        BOOST_CHECK_EQUAL(waitForValue(p0, kFail), kRes);
+        BOOST_CHECK_EQUAL(waitForValue(p1, kFail), kRes);
+        BOOST_CHECK_EQUAL(waitForValue(p2, kFail), kRes);
+    }
+    { // Static member functions.
+        auto p0 = Promise<float>::reject(kErr).fail(&PromiseContext::stringToFloatNoArg);
+        auto p1 = Promise<float>::reject(kErr).fail(&PromiseContext::stringToFloatArgByVal);
+        auto p2 = Promise<float>::reject(kErr).fail(&PromiseContext::stringToFloatArgByRef);
+
+        BOOST_CHECK_EQUAL(waitForValue(p0, kFail), kRes);
+        BOOST_CHECK_EQUAL(waitForValue(p1, kFail), kRes);
+        BOOST_CHECK_EQUAL(waitForValue(p2, kFail), kRes);
+    }
+}
+
 BOOST_AUTO_TEST_CASE(Then) {
     std::vector<std::variant<int, std::string>> values;
     auto input = Promise<int>::resolve(42);
@@ -34,8 +744,6 @@ BOOST_AUTO_TEST_CASE(Then) {
 
     BOOST_CHECK_EQUAL(input.isFulfilled(), true);
     BOOST_CHECK_EQUAL(output.isFulfilled(), true);
-
-    // auto p= new int;
 }
 
 BOOST_AUTO_TEST_CASE(ThenResolveAsync) {
@@ -140,7 +848,6 @@ BOOST_AUTO_TEST_CASE(ThenNullHandler) {
 }
 
 const float kRes = 0.42f;
-const float kFail = -1.f;
 
 float fnNoArg() {
     return kRes;
@@ -153,54 +860,24 @@ float fnArgByRef(const float &v) {
     return v;
 }
 
-class Klass {
-public: // STATICS
-    static float kFnNoArg() {
-        return kRes;
-    }
-    static float kFnArgByVal(float v) {
-        return v;
-    }
-    static float kFnArgByRef(const float &v) {
-        return v;
-    }
-
-public:
-    Klass(float v) : m_v{v} {
-    }
-
-    float fnNoArg() const {
-        return m_v;
-    }
-    float fnArgByVal(float v) const {
-        return v + m_v;
-    }
-    float fnArgByRef(const float &v) const {
-        return v + m_v;
-    }
-
-private:
-    const float m_v;
-};
-
-BOOST_AUTO_TEST_CASE(ThenFunctionPtrHandlers) {
+BOOST_FIXTURE_TEST_CASE(ThenFunctionPtrHandlers, PromiseContext) {
     { // Global functions.
         auto p0 = Promise<void>::resolve().then(&fnNoArg);
-        auto p1 = Promise<float>::resolve(kRes).then(&fnArgByVal);
+        auto p1 = Promise<float>::resolve(PromiseContext::kRes).then(&fnArgByVal);
         auto p2 = Promise<float>::resolve(kRes).then(&fnArgByRef);
 
-        BOOST_CHECK_EQUAL(waitForValue(p0, kFail), kRes);
-        BOOST_CHECK_EQUAL(waitForValue(p1, kFail), kRes);
-        BOOST_CHECK_EQUAL(waitForValue(p2, kFail), kRes);
+        BOOST_CHECK_EQUAL(waitForValue(p0, kFail), PromiseContext::kRes);
+        BOOST_CHECK_EQUAL(waitForValue(p1, kFail), PromiseContext::kRes);
+        BOOST_CHECK_EQUAL(waitForValue(p2, kFail), PromiseContext::kRes);
     }
     { // Static member functions.
-        auto p0 = Promise<void>::resolve().then(&Klass::kFnNoArg);
-        auto p1 = Promise<float>::resolve(kRes).then(&Klass::kFnArgByVal);
-        auto p2 = Promise<float>::resolve(kRes).then(&Klass::kFnArgByRef);
+        auto p0 = Promise<void>::resolve().then(&PromiseContext::kFnNoArg);
+        auto p1 = Promise<float>::resolve(PromiseContext::kRes).then(&PromiseContext::kFnArgByVal);
+        auto p2 = Promise<float>::resolve(PromiseContext::kRes).then(&PromiseContext::kFnArgByRef);
 
-        BOOST_CHECK_EQUAL(waitForValue(p0, kFail), kRes);
-        BOOST_CHECK_EQUAL(waitForValue(p1, kFail), kRes);
-        BOOST_CHECK_EQUAL(waitForValue(p2, kFail), kRes);
+        BOOST_CHECK_EQUAL(waitForValue(p0, kFail), PromiseContext::kRes);
+        BOOST_CHECK_EQUAL(waitForValue(p1, kFail), PromiseContext::kRes);
+        BOOST_CHECK_EQUAL(waitForValue(p2, kFail), PromiseContext::kRes);
     }
 }
 
@@ -242,23 +919,22 @@ BOOST_AUTO_TEST_CASE(ThenStdFunctionHandlers) {
     }
 }
 
-BOOST_AUTO_TEST_CASE(ThenStdBindHandlers) {
+BOOST_FIXTURE_TEST_CASE(ThenStdBindHandlers, PromiseContext) {
     using namespace std::placeholders;
+    const float value = 42.f;
+    this->setValue(value);
 
-    const float val{42.f};
-    const Klass obj{val};
-
-    const std::function<float()> bindNoArg = std::bind(&Klass::fnNoArg, &obj);
-    const std::function<float(float)> bindArgByVal = std::bind(&Klass::fnArgByVal, &obj, _1);
-    const std::function<float(const float &)> bindArgByRef = std::bind(&Klass::fnArgByRef, &obj, _1);
+    const std::function<float()> bindNoArg = std::bind(&PromiseContext::functionNoArg, this);
+    const std::function<float(float)> bindArgByVal = std::bind(&PromiseContext::functionArgByVal, this, _1);
+    const std::function<float(const float &)> bindArgByRef = std::bind(&PromiseContext::functionArgByRef, this, _1);
 
     auto p0 = Promise<void>::resolve().then(bindNoArg);
     auto p1 = Promise<float>::resolve(kRes).then(bindArgByVal);
     auto p2 = Promise<float>::resolve(kRes).then(bindArgByRef);
 
-    BOOST_CHECK_EQUAL(waitForValue(p0, kFail), val);
-    BOOST_CHECK_EQUAL(waitForValue(p1, kFail), val + kRes);
-    BOOST_CHECK_EQUAL(waitForValue(p2, kFail), val + kRes);
+    BOOST_CHECK_EQUAL(waitForValue(p0, kFail), value);
+    BOOST_CHECK_EQUAL(waitForValue(p1, kFail), value + kRes);
+    BOOST_CHECK_EQUAL(waitForValue(p2, kFail), value + kRes);
 }
 
 BOOST_AUTO_TEST_CASE(ThenLambdaHandlers) {
@@ -297,4 +973,6 @@ BOOST_AUTO_TEST_CASE(ThenLambdaHandlers) {
         BOOST_CHECK_EQUAL(waitForValue(p1, kFail), kRes);
         BOOST_CHECK_EQUAL(waitForValue(p2, kFail), kRes);
     }
-}
\ No newline at end of file
+}
+
+BOOST_AUTO_TEST_SUITE_END()
\ No newline at end of file
diff --git a/Universal/BoostLog.cpp b/Universal/BoostLog.cpp
index 0200be6..54ef8b6 100644
--- a/Universal/BoostLog.cpp
+++ b/Universal/BoostLog.cpp
@@ -26,8 +26,7 @@ void initialize(const std::string &filename, const std::string &target, boost::l
 #else
         std::ostringstream oss;
         oss << filename << "_%Y-%m-%d_%H.%M.%S_%N.log";
-        auto fileSink =
-            add_file_log(keywords::file_name = oss.str(), keywords::auto_flush = true, keywords::target = target);
+        auto fileSink = add_file_log(keywords::file_name = oss.str(), keywords::auto_flush = true, keywords::target = target);
         fileSink->set_formatter(&defaultFormatter);
 #endif
         initialized = true;
@@ -41,12 +40,11 @@ void defaultFormatter(const boost::log::record_view &record, boost::log::formatt
     boost::log::formatting_ostream oss(level);
     oss << "[" << record[boost::log::trivial::severity] << "]";
 
-    auto dateTimeFormatter = expressions::stream << expressions::format_date_time<boost::posix_time::ptime>(
-                                 "TimeStamp", "[%m-%d %H:%M:%S.%f]");
+    auto dateTimeFormatter = expressions::stream
+                             << expressions::format_date_time<boost::posix_time::ptime>("TimeStamp", "[%m-%d %H:%M:%S.%f]");
 
     dateTimeFormatter(record, ostream);
-    ostream << "[" << boost::log::extract<boost::log::attributes::current_thread_id::value_type>("ThreadID", record)
-            << "]";
+    ostream << "[" << boost::log::extract<boost::log::attributes::current_thread_id::value_type>("ThreadID", record) << "]";
     ostream << std::setw(8) << std::left << level;
     auto &&category = record[AmassKeywords::category];
     if (!category.empty()) ostream << " [" << category << "]";
@@ -82,3 +80,14 @@ BOOST_LOG_GLOBAL_LOGGER_INIT(location_logger, LocationLogger<boost::log::trivial
     }
     return lg;
 }
+
+namespace std {
+ostream &operator<<(ostream &os, const map<int, int> &m) {
+    os << "{ ";
+    for (const auto &pair : m) {
+        os << "{" << pair.first << ", " << pair.second << "} ";
+    }
+    os << "}";
+    return os;
+}
+} // namespace std
\ No newline at end of file
diff --git a/Universal/BoostLog.inl b/Universal/BoostLog.inl
index 66b8c4f..f474318 100644
--- a/Universal/BoostLog.inl
+++ b/Universal/BoostLog.inl
@@ -21,7 +21,9 @@ public:
         }
         return ret;
     }
-    inline bool doOnceInterface() const { return static_cast<const Derived *>(this)->doOnce(); }
+    inline bool doOnceInterface() const {
+        return static_cast<const Derived *>(this)->doOnce();
+    }
 
 protected:
     mutable bool m_status = true;
@@ -29,8 +31,11 @@ protected:
 
 class NumberPredicator : public LogPredicator<NumberPredicator> {
 public:
-    NumberPredicator(int limit) : m_limit(limit) {}
-    inline bool doOnce() const { return (m_current++ % m_limit) == 0; }
+    NumberPredicator(int limit) : m_limit(limit) {
+    }
+    inline bool doOnce() const {
+        return (m_current++ % m_limit) == 0;
+    }
 
 private:
     int m_limit;
@@ -39,8 +44,11 @@ private:
 
 class CountPredicator : public LogPredicator<CountPredicator> {
 public:
-    CountPredicator(int limit) : m_limit(limit) {}
-    inline bool doOnce() const { return m_current++ < m_limit; }
+    CountPredicator(int limit) : m_limit(limit) {
+    }
+    inline bool doOnce() const {
+        return m_current++ < m_limit;
+    }
 
 private:
     int m_limit;
@@ -49,7 +57,8 @@ private:
 
 class TimePredicator : public LogPredicator<TimePredicator> {
 public:
-    TimePredicator(int milliseconds) : m_limit(std::chrono::milliseconds(milliseconds)) {}
+    TimePredicator(int milliseconds) : m_limit(std::chrono::milliseconds(milliseconds)) {
+    }
 
     inline bool doOnce() const {
         auto now = std::chrono::system_clock::now();
@@ -65,8 +74,7 @@ private:
 };
 
 template <typename BaseT>
-CategoryTaggerFeature<BaseT>::CategoryTaggerFeature(const CategoryTaggerFeature &obj)
-    : BaseT(static_cast<const BaseT &>(obj)) {
+CategoryTaggerFeature<BaseT>::CategoryTaggerFeature(const CategoryTaggerFeature &obj) : BaseT(static_cast<const BaseT &>(obj)) {
 }
 
 template <typename BaseT>
@@ -96,13 +104,13 @@ boost::log::record CategoryTaggerFeature<BaseT>::open_record_unlocked(const Args
 }
 
 template <typename BaseT>
-FilenameTaggerFeature<BaseT>::FilenameTaggerFeature(const FilenameTaggerFeature &obj)
-    : BaseT(static_cast<const BaseT &>(obj)) {
+FilenameTaggerFeature<BaseT>::FilenameTaggerFeature(const FilenameTaggerFeature &obj) : BaseT(static_cast<const BaseT &>(obj)) {
 }
 
 template <typename BaseT>
 template <typename ArgsT>
-FilenameTaggerFeature<BaseT>::FilenameTaggerFeature(const ArgsT &args) : BaseT(args) {}
+FilenameTaggerFeature<BaseT>::FilenameTaggerFeature(const ArgsT &args) : BaseT(args) {
+}
 
 template <typename BaseT>
 template <typename ArgsT>
@@ -126,13 +134,13 @@ boost::log::record FilenameTaggerFeature<BaseT>::open_record_unlocked(const Args
 }
 
 template <typename BaseT>
-FunctionTaggerFeature<BaseT>::FunctionTaggerFeature(const FunctionTaggerFeature &obj)
-    : BaseT(static_cast<const BaseT &>(obj)) {
+FunctionTaggerFeature<BaseT>::FunctionTaggerFeature(const FunctionTaggerFeature &obj) : BaseT(static_cast<const BaseT &>(obj)) {
 }
 
 template <typename BaseT>
 template <typename ArgsT>
-FunctionTaggerFeature<BaseT>::FunctionTaggerFeature(const ArgsT &args) : BaseT(args) {}
+FunctionTaggerFeature<BaseT>::FunctionTaggerFeature(const ArgsT &args) : BaseT(args) {
+}
 
 template <typename BaseT>
 template <typename ArgsT>
@@ -157,10 +165,12 @@ boost::log::record FunctionTaggerFeature<BaseT>::open_record_unlocked(const Args
 
 template <typename BaseT>
 template <typename ArgsT>
-LineTaggerFeature<BaseT>::LineTaggerFeature(const ArgsT &args) : BaseT(args) {}
+LineTaggerFeature<BaseT>::LineTaggerFeature(const ArgsT &args) : BaseT(args) {
+}
 
 template <typename BaseT>
-LineTaggerFeature<BaseT>::LineTaggerFeature(const LineTaggerFeature &obj) : BaseT(static_cast<const BaseT &>(obj)) {}
+LineTaggerFeature<BaseT>::LineTaggerFeature(const LineTaggerFeature &obj) : BaseT(static_cast<const BaseT &>(obj)) {
+}
 
 template <typename BaseT>
 template <typename ArgsT>
@@ -182,4 +192,8 @@ boost::log::record LineTaggerFeature<BaseT>::open_record_unlocked(const ArgsT &a
     return BaseT::open_record_unlocked(args);
 }
 
+namespace std {
+ostream &operator<<(ostream &os, const map<int, int> &m);
+}
+
 #endif // BOOSTLOG_INL
diff --git a/Universal/FunctionTraits.h b/Universal/FunctionTraits.h
index 8673075..2a85653 100644
--- a/Universal/FunctionTraits.h
+++ b/Universal/FunctionTraits.h
@@ -124,9 +124,6 @@ typename FunctionTraits<std::decay_t<Function>>::StlFunctionType makeStlFunction
     return static_cast<typename FunctionTraits<std::decay_t<Function>>::StlFunctionType>(std::forward<Function>(lambda));
 }
 
-template <typename T>
-using Unqualified = typename std::remove_cv<typename std::remove_reference<T>::type>::type;
-
 /*!
  * \struct HasCallOperator
  * http://stackoverflow.com/a/5117641
diff --git a/Universal/IoContext.h b/Universal/IoContext.h
index 86ececf..bc53a2f 100644
--- a/Universal/IoContext.h
+++ b/Universal/IoContext.h
@@ -3,6 +3,8 @@
 
 #include "Singleton.h"
 #include <boost/asio/io_context.hpp>
+#include <boost/asio/post.hpp>
+#include <boost/asio/steady_timer.hpp>
 #include <thread>
 
 class IoContext {
@@ -12,7 +14,9 @@ public:
         Asynchronous,
     };
     friend class Amass::Singleton<IoContext, Amass::LocalInstance>;
-    std::shared_ptr<boost::asio::io_context> ioContext() const { return m_ioContext; }
+    std::shared_ptr<boost::asio::io_context> ioContext() const {
+        return m_ioContext;
+    }
     template <Mode mode = Mode::Asynchronous>
     void run() {
         if constexpr (mode == Mode::Asynchronous) {
@@ -24,9 +28,28 @@ public:
     void stop();
     ~IoContext();
 
+    /**
+     * @brief 
+     * 
+     * @tparam Executor boost::asio::io_context、boost::asio::strand(通过 boost::asio::make_strand(io_context); 得到)
+     */
+    template <class Executor, class Func, class Rep, class Period>
+    static void postDelayed(Executor &ioContext, Func &&task, const std::chrono::duration<Rep, Period> &duration) {
+        auto timer = std::make_shared<boost::asio::steady_timer>(ioContext, duration);
+        timer->async_wait([timer, task = std::forward<Func>(task)](const boost::system::error_code & /*e*/) mutable {
+            boost::asio::post(timer->get_executor(), std::move(task));
+        });
+    }
+
+    template <class Executor, class Func>
+    static void postDelayed(Executor &ioContext, Func &&task, int milliseconds) {
+        return postDelayed(ioContext, std::forward(task), std::chrono::milliseconds(milliseconds));
+    }
+
 protected:
     template <typename... Args>
-    IoContext(Args &&... args) : m_ioContext(std::make_shared<boost::asio::io_context>(std::forward<Args>(args)...)) {}
+    IoContext(Args &&...args) : m_ioContext(std::make_shared<boost::asio::io_context>(std::forward<Args>(args)...)) {
+    }
     void runIoContext();
 
 private:
diff --git a/Universal/Private/PromiseData.h b/Universal/Private/PromiseData.h
index 28f2271..d817c39 100644
--- a/Universal/Private/PromiseData.h
+++ b/Universal/Private/PromiseData.h
@@ -180,4 +180,35 @@ protected:
     }
 };
 
+template <typename T, typename U, bool IsConvertibleViaStaticCast>
+struct PromiseConverterBase;
+
+template <typename T, typename U>
+struct PromiseConverterBase<T, U, true> {
+    static std::function<U(const T &)> create() {
+        return [](const T &value) { return static_cast<U>(value); };
+    }
+};
+
+template <typename T, typename U>
+struct PromiseConverterBase<T, U, false> {
+    static std::function<U(const T &)> create() {
+        return [](const T &value) {
+            throw PromiseConversionException{};
+            return U{};
+        };
+    }
+};
+
+template <typename T, typename U>
+struct PromiseConverter : PromiseConverterBase<T, U,
+                                               // Fundamental types and converting constructors.
+                                               std::is_convertible<T, U>::value ||
+                                                   // Conversion to void.
+                                                   std::is_same<U, void>::value ||
+                                                   // Conversion between enums and arithmetic types.
+                                                   ((std::is_enum<T>::value && std::is_arithmetic<U>::value) ||
+                                                    (std::is_arithmetic<T>::value && std::is_enum<U>::value) ||
+                                                    (std::is_enum<T>::value && std::is_enum<U>::value))> {};
+
 #endif // __PROMISEDATA_H__
\ No newline at end of file
diff --git a/Universal/Private/PromiseException.h b/Universal/Private/PromiseException.h
deleted file mode 100644
index a3b5b1b..0000000
--- a/Universal/Private/PromiseException.h
+++ /dev/null
@@ -1,10 +0,0 @@
-#ifndef __PROMISEEXCEPTION_H__
-#define __PROMISEEXCEPTION_H__
-
-#include <exception>
-
-class PromiseUndefinedException : public std::exception {
-public:
-};
-
-#endif // __PROMISEEXCEPTION_H__
\ No newline at end of file
diff --git a/Universal/Private/PromiseHandler.h b/Universal/Private/PromiseHandler.h
index 5504592..ae77cbc 100644
--- a/Universal/Private/PromiseHandler.h
+++ b/Universal/Private/PromiseHandler.h
@@ -2,9 +2,9 @@
 #define __PROMISEHANDLER_H__
 
 #include "../FunctionTraits.h"
-#include <type_traits>
-#include <exception>
 #include "PromiseData.h"
+#include <exception>
+#include <type_traits>
 
 template <typename T>
 class Promise;
@@ -26,6 +26,12 @@ struct PromiseDeduce<const volatile T> : public PromiseDeduce<T> {};
 template <typename T>
 struct PromiseDeduce<Promise<T>> : public PromiseDeduce<T> {};
 
+template <typename Functor, typename... Args>
+struct PromiseFunctor {
+    using ResultType = typename std::invoke_result_t<Functor, Args...>;
+    using PromiseType = typename PromiseDeduce<ResultType>::Type;
+};
+
 template <typename T>
 struct PromiseFulfill {
     template <typename V, typename TResolve, typename TReject>
diff --git a/Universal/Private/PromiseResolver.h b/Universal/Private/PromiseResolver.h
index b17d489..0fb5e32 100644
--- a/Universal/Private/PromiseResolver.h
+++ b/Universal/Private/PromiseResolver.h
@@ -1,8 +1,6 @@
 #ifndef __PROMISERESOLVER_H__
 #define __PROMISERESOLVER_H__
 
-#include "PromiseException.h"
-
 template <typename T>
 class Promise;
 
diff --git a/Universal/Promise.h b/Universal/Promise.h
index eba3f55..d3372af 100644
--- a/Universal/Promise.h
+++ b/Universal/Promise.h
@@ -1,6 +1,16 @@
 #ifndef __PROMISE_H__
 #define __PROMISE_H__
 
+#include <exception>
+
+class PromiseUndefinedException : public std::exception {
+public:
+};
+
+class PromiseConversionException : public std::exception {
+public:
+};
+
 #include "Private/PromiseHandler.h"
 #include "Private/PromiseResolver.h"
 #include <thread>
@@ -42,6 +52,25 @@ public:
         swap(other);
     }
 
+    virtual ~PromiseBase() {
+    }
+
+    PromiseBase<T> &operator=(const PromiseBase<T> &other) {
+        m_d = other.m_d;
+        return *this;
+    }
+    PromiseBase<T> &operator=(PromiseBase<T> &&other) {
+        PromiseBase<T>(std::move(other)).swap(*this);
+        return *this;
+    }
+
+    bool operator==(const PromiseBase<T> &other) const {
+        return (m_d == other.m_d);
+    }
+    bool operator!=(const PromiseBase<T> &other) const {
+        return (m_d != other.m_d);
+    }
+
     void swap(PromiseBase<T> &other) {
         std::swap(m_d, other.m_d);
     }
@@ -78,6 +107,12 @@ public:
         return then(std::forward<TFulfilled>(fulfilled), nullptr);
     }
 
+    template <typename THandler>
+    Promise<T> finally(THandler handler) const {
+        Promise<T> p = *this;
+        return p.then(handler, handler).then([=]() { return p; });
+    }
+
     template <typename TRejected>
     typename PromiseHandler<T, std::nullptr_t>::PromiseType fail(TRejected &&rejected) const {
         return then(nullptr, std::forward<TRejected>(rejected));
@@ -95,10 +130,112 @@ public:
         return Promise<T>{[&](const PromiseResolve<T> &, const PromiseReject<T> &reject) { reject(std::forward<E>(error)); }};
     }
 
+    template <typename THandler>
+    Promise<T> tapFail(THandler handler) const {
+        Promise<T> p = *this;
+        return p.then([]() {}, handler).then([=]() { return p; });
+    }
+
+    template <typename THandler>
+    Promise<T> tap(THandler handler) const {
+        Promise<T> p = *this;
+        return p.then(handler).then([=]() { return p; });
+    }
+
+#ifdef BOOST_ASIO_EXECUTION_EXECUTOR
+    template <class Executor, class Rep, class Period>
+    Promise<T> delay(Executor &ioContext, const std::chrono::duration<Rep, Period> &duration) const {
+        return tap([&]() {
+            return Promise<void>{[&](const PromiseResolve<void> &resolve) {
+                auto timer = std::make_shared<boost::asio::steady_timer>(ioContext, duration);
+                timer->async_wait([timer, resolve](const boost::system::error_code & /*e*/) mutable {
+                    boost::asio::post(timer->get_executor(), resolve);
+                });
+            }};
+        });
+    }
+
+    template <class Executor>
+    Promise<T> delay(Executor &ioContext, int milliseconds) const {
+        return delay(ioContext, std::chrono::milliseconds(milliseconds));
+    }
+#endif
+
 protected:
     std::shared_ptr<PromiseData<T>> m_d;
 };
 
+namespace PromiseHelper {
+template <typename T>
+typename PromiseDeduce<T>::Type resolve(T &&value) {
+    using PromiseType = typename PromiseDeduce<T>::Type;
+    using ValueType = typename PromiseType::Type;
+    using ResolveType = PromiseResolve<ValueType>;
+    using RejectType = PromiseReject<ValueType>;
+
+    return PromiseType{[&](ResolveType &&resolve, RejectType &&reject) {
+        PromiseFulfill<std::decay_t<T>>::call(std::forward<T>(value), std::forward<ResolveType>(resolve), std::forward<RejectType>(reject));
+    }};
+}
+
+Promise<void> resolve();
+
+template <typename Functor, typename... Args>
+typename PromiseFunctor<Functor, Args...>::PromiseType attempt(Functor &&fn, Args &&...args) {
+    using FunctorType = PromiseFunctor<Functor, Args...>;
+    using PromiseType = typename FunctorType::PromiseType;
+    using ValueType = typename PromiseType::Type;
+
+    // NOTE: std::forward<T<U>>: MSVC 2013 fails when forwarding
+    // template type (error: "expects 4 arguments - 0 provided").
+    // However it succeeds with type alias.
+    // TODO: should we expose QPromise::ResolveType & RejectType?
+    using ResolveType = PromiseResolve<ValueType>;
+    using RejectType = PromiseReject<ValueType>;
+
+    return PromiseType{[&](ResolveType &&resolve, RejectType &&reject) {
+        PromiseDispatch<typename FunctorType::ResultType>::call(std::forward<ResolveType>(resolve), std::forward<RejectType>(reject),
+                                                                std::forward<Functor>(fn), std::forward<Args>(args)...);
+    }};
+}
+
+template <typename T, template <typename, typename...> class Sequence = std::vector, typename... Args>
+Promise<std::vector<T>> all(const Sequence<Promise<T>, Args...> &promises) {
+    const int count = static_cast<int>(promises.size());
+    if (count == 0) {
+        return PromiseHelper::resolve(std::vector<T>{});
+    }
+
+    return Promise<std::vector<T>>{[=](const PromiseResolve<std::vector<T>> &resolve, const PromiseReject<std::vector<T>> &reject) {
+        auto remaining = std::make_shared<int>(count);
+        auto results = std::make_shared<std::vector<T>>(count);
+
+        int i = 0;
+        for (const auto &promise : promises) {
+            promise.then(
+                [=](const T &res) mutable {
+                    (*results)[i] = res;
+                    if (--(*remaining) == 0) {
+                        resolve(*results);
+                    }
+                },
+                [=]() mutable {
+                    if (*remaining != -1) {
+                        *remaining = -1;
+                        reject(std::current_exception());
+                    }
+                });
+
+            i++;
+        }
+    }};
+}
+
+template <template <typename, typename...> class Sequence = std::vector, typename... Args>
+Promise<void> all(const Sequence<Promise<void>, Args...> &promises);
+
+}; // namespace PromiseHelper
+
 template <typename T>
 class Promise : public PromiseBase<T> {
     friend class PromiseResolver<T>;
@@ -108,6 +245,30 @@ public:
     Promise(F &&resolver) : PromiseBase<T>(std::forward<F>(resolver)) {
     }
 
+    template <typename U>
+    Promise<U> convert() const {
+        return PromiseBase<T>::then(PromiseConverter<T, U>::create());
+    }
+
+    template <typename Functor>
+    Promise<T> each(Functor fn) {
+        return this->tap([=](const T &values) {
+            int i = 0;
+
+            std::vector<Promise<void>> promises;
+            for (const auto &v : values) {
+                promises.push_back(PromiseHelper::attempt(fn, v, i).then([]() {
+                    // Cast to void in case fn returns a non promise value.
+                    // TODO remove when implicit cast is implemented.
+                }));
+
+                i++;
+            }
+
+            return PromiseHelper::all(promises);
+        });
+    }
+
     static Promise<T> resolve(const T &value) {
         return Promise<T>{[&](const PromiseResolve<T> &resolve) { resolve(value); }};
     }
@@ -131,4 +292,36 @@ private:
     friend class PromiseBase<void>;
 };
 
+namespace PromiseHelper {
+Promise<void> resolve() {
+    return Promise<void>{[](const PromiseResolve<void> &resolve) { resolve(); }};
+}
+
+template <template <typename, typename...> class Sequence = std::vector, typename... Args>
+Promise<void> all(const Sequence<Promise<void>, Args...> &promises) {
+    const int count = static_cast<int>(promises.size());
+    if (count == 0) {
+        return PromiseHelper::resolve();
+    }
+
+    return Promise<void>{[=](const PromiseResolve<void> &resolve, const PromiseReject<void> &reject) {
+        auto remaining = std::make_shared<int>(count);
+        for (const auto &promise : promises) {
+            promise.then(
+                [=]() {
+                    if (--(*remaining) == 0) {
+                        resolve();
+                    }
+                },
+                [=]() {
+                    if (*remaining != -1) {
+                        *remaining = -1;
+                        reject(std::current_exception());
+                    }
+                });
+        }
+    }};
+}
+} // namespace PromiseHelper
+
 #endif // __PROMISE_H__
\ No newline at end of file
diff --git a/resource/deploy.sh b/resource/deploy.sh
index 5377215..2eb8ace 100755
--- a/resource/deploy.sh
+++ b/resource/deploy.sh
@@ -67,6 +67,7 @@ function build() {
         exit 1
     fi
     $build_path/UnitTest/UnitTest
+    # valgrind --leak-check=full $build_path/UnitTest/UnitTest
 }
 
 function main() {