AK: Add a Tuple implementation

Please don't use this outside of metaprogramming needs, *please*.

AK/Tuple.h

@@ -0,0 +1,218 @@
+/*
+ * Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/StdLibExtras.h>
+#include <AK/TypeList.h>
+
+namespace AK::Detail {
+
+template<typename... Ts>
+struct Tuple {
+};
+
+template<typename T>
+struct Tuple<T> {
+    Tuple(T&& value) requires(!IsSame<T&&, const T&>)
+        : value(forward<T>(value))
+    {
+    }
+
+    Tuple(const T& value)
+        : value(value)
+    {
+    }
+
+    template<typename U>
+    U& get()
+    {
+        static_assert(IsSame<T, U>, "Invalid tuple access");
+        return value;
+    }
+
+    template<typename U>
+    const U& get() const
+    {
+        return const_cast<Tuple<T>&>(*this).get<U>();
+    }
+
+    template<typename U, unsigned index>
+    U& get_with_index()
+    {
+        static_assert(IsSame<T, U> && index == 0, "Invalid tuple access");
+        return value;
+    }
+
+    template<typename U, unsigned index>
+    const U& get_with_index() const
+    {
+        return const_cast<Tuple<T>&>(*this).get_with_index<U, index>();
+    }
+
+private:
+    T value;
+};
+
+template<typename T, typename... TRest>
+struct Tuple<T, TRest...> : Tuple<TRest...> {
+    Tuple(T&& first, TRest&&... rest)
+        : Tuple<TRest...>(forward<TRest>(rest)...)
+        , value(forward<T>(first))
+    {
+    }
+
+    Tuple(const T& first, const TRest&... rest)
+        : Tuple<TRest...>(rest...)
+        , value(first)
+    {
+    }
+
+    template<typename U>
+    U& get()
+    {
+        if constexpr (IsSame<T, U>)
+            return value;
+        else
+            return Tuple<TRest...>::template get<U>();
+    }
+
+    template<typename U>
+    const U& get() const
+    {
+        return const_cast<Tuple<T, TRest...>&>(*this).get<U>();
+    }
+
+    template<typename U, unsigned index>
+    U& get_with_index()
+    {
+        if constexpr (IsSame<T, U> && index == 0)
+            return value;
+        else
+            return Tuple<TRest...>::template get_with_index<U, index - 1>();
+    }
+
+    template<typename U, unsigned index>
+    const U& get_with_index() const
+    {
+        return const_cast<Tuple<T, TRest...>&>(*this).get_with_index<U, index>();
+    }
+
+private:
+    T value;
+};
+
+}
+
+namespace AK {
+
+template<typename... Ts>
+struct Tuple : Detail::Tuple<Ts...> {
+    using Types = TypeList<Ts...>;
+    using Detail::Tuple<Ts...>::Tuple;
+    using Indices = MakeIndexSequence<sizeof...(Ts)>;
+
+    Tuple(Tuple&& other)
+        : Tuple(move(other), Indices())
+    {
+    }
+
+    Tuple(const Tuple& other)
+        : Tuple(other, Indices())
+    {
+    }
+
+    Tuple& operator=(Tuple&& other)
+    {
+        set(move(other), Indices());
+        return *this;
+    }
+
+    Tuple& operator=(const Tuple& other)
+    {
+        set(other, Indices());
+        return *this;
+    }
+
+    template<typename T>
+    auto& get()
+    {
+        return Detail::Tuple<Ts...>::template get<T>();
+    }
+
+    template<unsigned index>
+    auto& get()
+    {
+        return Detail::Tuple<Ts...>::template get_with_index<typename Types::template Type<index>, index>();
+    }
+
+    template<typename T>
+    auto& get() const
+    {
+        return Detail::Tuple<Ts...>::template get<T>();
+    }
+
+    template<unsigned index>
+    auto& get() const
+    {
+        return Detail::Tuple<Ts...>::template get_with_index<typename Types::template Type<index>, index>();
+    }
+
+    template<typename F>
+    auto apply_as_args(F&& f)
+    {
+        return apply_as_args(forward<F>(f), Indices());
+    }
+
+    template<typename F>
+    auto apply_as_args(F&& f) const
+    {
+        return apply_as_args(forward<F>(f), Indices());
+    }
+
+    static constexpr auto size() { return sizeof...(Ts); }
+
+private:
+    template<unsigned... Is>
+    Tuple(Tuple&& other, IndexSequence<Is...>)
+        : Detail::Tuple<Ts...>(move(other.get<Is>())...)
+    {
+    }
+
+    template<unsigned... Is>
+    Tuple(const Tuple& other, IndexSequence<Is...>)
+        : Detail::Tuple<Ts...>(other.get<Is>()...)
+    {
+    }
+
+    template<unsigned... Is>
+    void set(Tuple&& other, IndexSequence<Is...>)
+    {
+        ((get<Is>() = move(other.get<Is>())), ...);
+    }
+
+    template<unsigned... Is>
+    void set(const Tuple& other, IndexSequence<Is...>)
+    {
+        ((get<Is>() = other.get<Is>()), ...);
+    }
+
+    template<typename F, unsigned... Is>
+    auto apply_as_args(F&& f, IndexSequence<Is...>)
+    {
+        return forward<F>(f)(get<Is>()...);
+    }
+
+    template<typename F, unsigned... Is>
+    auto apply_as_args(F&& f, IndexSequence<Is...>) const
+    {
+        return forward<F>(f)(get<Is>()...);
+    }
+};
+
+}
+
+using AK::Tuple;

Tests/AK/CMakeLists.txt

@@ -52,6 +52,7 @@ set(AK_TEST_SOURCES
     TestStringView.cpp
     TestTime.cpp
     TestTrie.cpp
+    TestTuple.cpp
     TestTypeTraits.cpp
     TestTypedTransfer.cpp
     TestURL.cpp

Tests/AK/TestTuple.cpp

@@ -0,0 +1,109 @@
+/*
+ * Copyright (c) 2021, Ali Mohammad Pur <mpfard@serenity.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibTest/TestSuite.h>
+
+#include <AK/Tuple.h>
+
+TEST_CASE(basic)
+{
+    Tuple<int, String> value { 1, "foo" };
+    EXPECT_EQ(value.get<int>(), 1);
+    EXPECT_EQ(value.get<String>(), "foo");
+    EXPECT_EQ(value.get<0>(), 1);
+    EXPECT_EQ(value.get<1>(), "foo");
+
+    // Move assignment
+    value = { 2, "bar" };
+    EXPECT_EQ(value.get<int>(), 2);
+    EXPECT_EQ(value.get<String>(), "bar");
+    EXPECT_EQ(value.get<0>(), 2);
+    EXPECT_EQ(value.get<1>(), "bar");
+
+    // Copy ctor
+    auto other_value { value };
+    EXPECT_EQ(other_value.get<int>(), 2);
+    EXPECT_EQ(other_value.get<String>(), "bar");
+    EXPECT_EQ(other_value.get<0>(), 2);
+    EXPECT_EQ(other_value.get<1>(), "bar");
+
+    // Move ctor
+    auto moved_to_value { move(value) };
+    EXPECT_EQ(moved_to_value.get<int>(), 2);
+    EXPECT_EQ(moved_to_value.get<String>(), "bar");
+    EXPECT_EQ(moved_to_value.get<0>(), 2);
+    EXPECT_EQ(moved_to_value.get<1>(), "bar");
+
+    // Copy assignment
+    value = moved_to_value;
+    EXPECT_EQ(moved_to_value.get<int>(), 2);
+    EXPECT_EQ(moved_to_value.get<String>(), "bar");
+    EXPECT_EQ(moved_to_value.get<0>(), 2);
+    EXPECT_EQ(moved_to_value.get<1>(), "bar");
+    EXPECT_EQ(value.get<int>(), 2);
+    EXPECT_EQ(value.get<String>(), "bar");
+    EXPECT_EQ(value.get<0>(), 2);
+    EXPECT_EQ(value.get<1>(), "bar");
+}
+
+TEST_CASE(no_copy)
+{
+    struct NoCopy {
+        AK_MAKE_NONCOPYABLE(NoCopy);
+
+    public:
+        NoCopy(NoCopy&&) = default;
+        NoCopy() = default;
+    };
+
+    // Deleted copy ctor should not cause an issue so long as the value isn't copied.
+    Tuple<NoCopy, int, int> value { {}, 1, 2 };
+    auto foo = move(value);
+    EXPECT_EQ(foo.get<1>(), 1);
+    EXPECT_EQ(foo.get<2>(), 2);
+}
+
+TEST_CASE(apply)
+{
+    Tuple<int, int, String> args { 1, 2, "foo" };
+
+    // With copy
+    {
+        bool was_called = false;
+        args.apply_as_args([&](int a, int b, String c) {
+            was_called = true;
+            EXPECT_EQ(a, 1);
+            EXPECT_EQ(b, 2);
+            EXPECT_EQ(c, "foo");
+        });
+        EXPECT(was_called);
+    }
+
+    // With reference
+    {
+        bool was_called = false;
+        args.apply_as_args([&](int& a, int& b, String& c) {
+            was_called = true;
+            EXPECT_EQ(a, 1);
+            EXPECT_EQ(b, 2);
+            EXPECT_EQ(c, "foo");
+        });
+        EXPECT(was_called);
+    }
+
+    // With const reference, taken from a const tuple
+    {
+        bool was_called = false;
+        const auto& args_ref = args;
+        args_ref.apply_as_args([&](const int& a, const int& b, const String& c) {
+            was_called = true;
+            EXPECT_EQ(a, 1);
+            EXPECT_EQ(b, 2);
+            EXPECT_EQ(c, "foo");
+        });
+        EXPECT(was_called);
+    }
+}