diff --git a/media/utils/include/mediautils/InPlaceFunction.h b/media/utils/include/mediautils/InPlaceFunction.h
new file mode 100644
index 0000000..8fa23e8
--- /dev/null
+++ b/media/utils/include/mediautils/InPlaceFunction.h
@@ -0,0 +1,267 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#pragma once
+
+#include <cstdlib>
+#include <functional>
+#include <memory>
+#include <type_traits>
+
+namespace android::mediautils {
+
+namespace detail {
+// Vtable interface for erased types
+template <typename Ret, typename... Args>
+struct ICallableTable {
+    // Destroy the erased type
+    void (*destroy)(void* storage) = nullptr;
+    // Call the erased object
+    Ret (*invoke)(void* storage, Args...) = nullptr;
+    // **Note** the next two functions only copy object data, not the vptr
+    // Copy the erased object to a new InPlaceFunction buffer
+    void (*copy_to)(const void* storage, void* other) = nullptr;
+    // Move the erased object to a new InPlaceFunction buffer
+    void (*move_to)(void* storage, void* other) = nullptr;
+};
+}  // namespace detail
+
+// This class is an *almost* drop-in replacement for std::function which is guaranteed to never
+// allocate, and always holds the type erased functional object in an in-line small buffer of
+// templated size. If the object is too large to hold, the type will fail to instantiate.
+//
+// Two notable differences are:
+// - operator() is not const (unlike std::function where the call operator is
+// const even if the erased type is not const callable). This retains const
+// correctness by default. A workaround is keeping InPlaceFunction mutable.
+// - Moving from an InPlaceFunction leaves the object in a valid state (operator
+// bool remains true), similar to std::optional/std::variant.
+// Calls to the object are still defined (and are equivalent
+// to calling the underlying type after it has been moved from). To opt-out
+// (and/or ensure safety), clearing the object is recommended:
+//      func1 = std::move(func2); // func2 still valid (and moved-from) after this line
+//      func2 = nullptr; // calling func2 will now abort
+template <typename, size_t BufferSize = 32>
+class InPlaceFunction;
+// We partially specialize to match types which are spelled like functions
+template <typename Ret, typename... Args, size_t BufferSize>
+class InPlaceFunction<Ret(Args...), BufferSize> {
+  public:
+    // Storage Type Details
+    static constexpr size_t Size = BufferSize;
+    static constexpr size_t Alignment = alignof(std::max_align_t);
+    using Buffer_t = std::aligned_storage_t<Size, Alignment>;
+    template <typename T, size_t Other>
+    friend class InPlaceFunction;
+
+  private:
+    // Callable which is used for empty InPlaceFunction objects (to match the
+    // std::function interface).
+    struct BadCallable {
+        [[noreturn]] Ret operator()(Args...) { std::abort(); }
+    };
+    static_assert(std::is_trivially_destructible_v<BadCallable>);
+
+    // Implementation of vtable interface for erased types.
+    // Contains only static vtable instantiated once for each erased type and
+    // static helpers.
+    template <typename T>
+    struct TableImpl {
+        // T should be a decayed type
+        static_assert(std::is_same_v<T, std::decay_t<T>>);
+
+        // Helper functions to get an unerased reference to the type held in the
+        // buffer. std::launder is required to avoid strict aliasing rules.
+        // The cast is always defined, as a precondition for these calls is that
+        // (exactly) a T was placement new constructed into the buffer.
+        constexpr static T& getRef(void* storage) {
+            return *std::launder(reinterpret_cast<T*>(storage));
+        }
+
+        constexpr static const T& getRef(const void* storage) {
+            return *std::launder(reinterpret_cast<const T*>(storage));
+        }
+
+        // Constexpr implies inline
+        constexpr static detail::ICallableTable<Ret, Args...> table = {
+                // Stateless lambdas are convertible to function ptrs
+                .destroy = [](void* storage) { getRef(storage).~T(); },
+                .invoke = [](void* storage, Args... args) -> Ret {
+                    return std::invoke(getRef(storage), args...);
+                },
+                .copy_to = [](const void* storage,
+                              void* other) { ::new (other) T(getRef(storage)); },
+                .move_to = [](void* storage,
+                              void* other) { ::new (other) T(std::move(getRef(storage))); },
+        };
+    };
+
+    // Check size/align requirements for the T in Buffer_t. We use a templated
+    // struct to enable std::conjunction (see below).
+    template <typename T>
+    struct WillFit : std::integral_constant<bool, sizeof(T) <= Size && alignof(T) <= Alignment> {};
+
+    // Check size/align requirements for a function to function conversion
+    template <typename T>
+    struct ConversionWillFit
+        : std::integral_constant<bool, (T::Size < Size) && (T::Alignment <= Alignment)> {};
+    template <typename T>
+    struct IsInPlaceFunction : std::false_type {};
+
+    template <size_t BufferSize_>
+    struct IsInPlaceFunction<InPlaceFunction<Ret(Args...), BufferSize_>> : std::true_type {};
+
+    // Pred is true iff T is a valid type to construct an InPlaceFunction with
+    // We use std::conjunction for readability and short-circuit behavior
+    // (checks are ordered).
+    // The actual target type is the decay of T.
+    template <typename T>
+    static constexpr bool Pred = std::conjunction_v<
+            std::negation<IsInPlaceFunction<std::decay_t<T>>>,   // T is not also an InPlaceFunction
+                                                                 // of the same signature.
+            std::is_invocable_r<Ret, std::decay_t<T>, Args...>,  // correct signature callable
+            WillFit<std::decay_t<T>>  // The target type fits in local storage
+            >;
+
+    template <typename T>
+    static constexpr bool ConvertibleFunc =
+            std::conjunction_v<IsInPlaceFunction<std::decay_t<T>>,  // implies correctly invokable
+                               ConversionWillFit<std::decay_t<T>>>;
+
+    // Members below
+    // This must come first for alignment
+    Buffer_t storage_;
+    const detail::ICallableTable<Ret, Args...>* vptr_;
+
+    constexpr void copy_to(InPlaceFunction& other) const {
+        vptr_->copy_to(std::addressof(storage_), std::addressof(other.storage_));
+        other.vptr_ = vptr_;
+    }
+
+    constexpr void move_to(InPlaceFunction& other) {
+        vptr_->move_to(std::addressof(storage_), std::addressof(other.storage_));
+        other.vptr_ = vptr_;
+    }
+
+    constexpr void destroy() { vptr_->destroy(std::addressof(storage_)); }
+
+    template <typename T, typename Target = std::decay_t<T>>
+    constexpr void genericInit(T&& t) {
+        vptr_ = &TableImpl<Target>::table;
+        ::new (std::addressof(storage_)) Target(std::forward<T>(t));
+    }
+
+    template <typename T, typename Target = std::decay_t<T>>
+    constexpr void convertingInit(T&& smallerFunc) {
+        // Redundant, but just in-case
+        static_assert(Target::Size < Size && Target::Alignment <= Alignment);
+        if constexpr (std::is_lvalue_reference_v<T>) {
+            smallerFunc.vptr_->copy_to(std::addressof(smallerFunc.storage_),
+                                         std::addressof(storage_));
+        } else {
+            smallerFunc.vptr_->move_to(std::addressof(smallerFunc.storage_),
+                                         std::addressof(storage_));
+        }
+        vptr_ = smallerFunc.vptr_;
+    }
+
+  public:
+    // Public interface
+    template <typename T, std::enable_if_t<Pred<T>>* = nullptr>
+    constexpr InPlaceFunction(T&& t) {
+        genericInit(std::forward<T>(t));
+    }
+
+    // Conversion from smaller functions.
+    template <typename T, std::enable_if_t<ConvertibleFunc<T>>* = nullptr>
+    constexpr InPlaceFunction(T&& t) {
+        convertingInit(std::forward<T>(t));
+    }
+
+    constexpr InPlaceFunction(const InPlaceFunction& other) { other.copy_to(*this); }
+
+    constexpr InPlaceFunction(InPlaceFunction&& other) { other.move_to(*this); }
+
+    // Making functions default constructible has pros and cons, we will align
+    // with the standard
+    constexpr InPlaceFunction() : InPlaceFunction(BadCallable{}) {}
+
+    constexpr InPlaceFunction(std::nullptr_t) : InPlaceFunction(BadCallable{}) {}
+#if __cplusplus >= 202002L
+    constexpr
+#endif
+    ~InPlaceFunction() {
+        destroy();
+    }
+
+    // The std::function call operator is marked const, but this violates const
+    // correctness. We deviate from the standard and do not mark the operator as
+    // const. Collections of InPlaceFunctions should probably be mutable.
+    constexpr Ret operator()(Args... args) {
+        return vptr_->invoke(std::addressof(storage_), args...);
+    }
+
+    constexpr InPlaceFunction& operator=(const InPlaceFunction& other) {
+        if (std::addressof(other) == this) return *this;
+        destroy();
+        other.copy_to(*this);
+        return *this;
+    }
+
+    constexpr InPlaceFunction& operator=(InPlaceFunction&& other) {
+        if (std::addressof(other) == this) return *this;
+        destroy();
+        other.move_to(*this);
+        return *this;
+    }
+
+    template <typename T, std::enable_if_t<Pred<T>>* = nullptr>
+    constexpr InPlaceFunction& operator=(T&& t) {
+        // We can't assign to ourselves, since T is a different type
+        destroy();
+        genericInit(std::forward<T>(t));
+        return *this;
+    }
+
+    // Explicitly defining this function saves a move/dtor
+    template <typename T, std::enable_if_t<ConvertibleFunc<T>>* = nullptr>
+    constexpr InPlaceFunction& operator=(T&& t) {
+        // We can't assign to ourselves, since T is different type
+        destroy();
+        convertingInit(std::forward<T>(t));
+        return *this;
+    }
+
+    constexpr InPlaceFunction& operator=(std::nullptr_t) { return operator=(BadCallable{}); }
+
+    // Moved from InPlaceFunctions are still considered valid (similar to
+    // std::optional). If using std::move on a function object explicitly, it is
+    // recommended that the object is reset using nullptr.
+    constexpr explicit operator bool() const { return vptr_ != &TableImpl<BadCallable>::table; }
+
+    constexpr void swap(InPlaceFunction& other) {
+        if (std::addressof(other) == this) return;
+        InPlaceFunction tmp{std::move(other)};
+        other.destroy();
+        move_to(other);
+        destroy();
+        tmp.move_to(*this);
+    }
+
+    friend constexpr void swap(InPlaceFunction& lhs, InPlaceFunction& rhs) { lhs.swap(rhs); }
+};
+
+}   // namespace android::mediautils
diff --git a/media/utils/tests/Android.bp b/media/utils/tests/Android.bp
index f0e3c1e..58f86be 100644
--- a/media/utils/tests/Android.bp
+++ b/media/utils/tests/Android.bp
@@ -178,3 +178,13 @@
         "extended_accumulator_tests.cpp",
     ],
 }
+
+cc_test {
+    name: "inplace_function_tests",
+
+    defaults: ["libmediautils_tests_defaults"],
+
+    srcs: [
+        "inplace_function_tests.cpp"
+    ],
+}
diff --git a/media/utils/tests/inplace_function_tests.cpp b/media/utils/tests/inplace_function_tests.cpp
new file mode 100644
index 0000000..407c616
--- /dev/null
+++ b/media/utils/tests/inplace_function_tests.cpp
@@ -0,0 +1,346 @@
+/*
+ * Copyright (C) 2022 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#define LOG_TAG "inplace_function_tests"
+
+#include <mediautils/InPlaceFunction.h>
+
+#include <type_traits>
+
+#include <gtest/gtest.h>
+#include <log/log.h>
+
+using namespace android;
+using namespace android::mediautils;
+
+struct BigCallable {
+    BigCallable(size_t* x, size_t val1, size_t val2) : ptr(x), a(val1), b(val2) {}
+    size_t* ptr;
+    size_t a;
+    size_t b;
+    size_t operator()(size_t input) const {
+        *ptr += a * 100 + b * 10 + input;
+        return 8;
+    }
+};
+
+TEST(InPlaceFunctionTests, Basic) {
+    size_t x = 5;
+    InPlaceFunction<size_t(size_t)> func;
+    {
+        BigCallable test{&x, 2, 3};
+        func = test;
+    }
+    EXPECT_EQ(func(2), 8ull);
+    EXPECT_EQ(x, 232ull + 5);
+}
+
+TEST(InPlaceFunctionTests, Invalid) {
+    InPlaceFunction<size_t(size_t)> func;
+    EXPECT_TRUE(!func);
+    InPlaceFunction<size_t(size_t)> func2{nullptr};
+    EXPECT_TRUE(!func2);
+    InPlaceFunction<size_t(size_t)> func3 = [](size_t x) { return x; };
+    EXPECT_TRUE(!(!func3));
+    func3 = nullptr;
+    EXPECT_TRUE(!func3);
+}
+
+TEST(InPlaceFunctionTests, MultiArg) {
+    InPlaceFunction<size_t(size_t, size_t, size_t)> func = [](size_t a, size_t b, size_t c) {
+        return a + b + c;
+    };
+    EXPECT_EQ(func(2, 3, 5), 2ull + 3 + 5);
+}
+struct Record {
+    Record(size_t m, size_t c, size_t d) : move_called(m), copy_called(c), dtor_called(d) {}
+    Record() {}
+    size_t move_called = 0;
+    size_t copy_called = 0;
+    size_t dtor_called = 0;
+    friend std::ostream& operator<<(std::ostream& os, const Record& record) {
+        return os << "Record, moves: " << record.move_called << ", copies: " << record.copy_called
+                  << ", dtor: " << record.dtor_called << '\n';
+    }
+};
+
+bool operator==(const Record& lhs, const Record& rhs) {
+    return lhs.move_called == rhs.move_called && lhs.copy_called == rhs.copy_called &&
+           lhs.dtor_called == rhs.dtor_called;
+}
+
+struct Noisy {
+    Record& ref;
+    size_t state;
+    Noisy(Record& record, size_t val) : ref(record), state(val) {}
+    Noisy(const Noisy& other) : ref(other.ref), state(other.state) { ref.copy_called++; }
+
+    Noisy(Noisy&& other) : ref(other.ref), state(other.state) { ref.move_called++; }
+    ~Noisy() { ref.dtor_called++; }
+
+    size_t operator()() { return state; }
+};
+
+TEST(InPlaceFunctionTests, CtorForwarding) {
+    Record record;
+    Noisy noisy{record, 17};
+    InPlaceFunction<size_t()> func{noisy};
+    EXPECT_EQ(record, Record(0, 1, 0)); // move, copy, dtor
+    EXPECT_EQ(func(), 17ull);
+    Record record2;
+    Noisy noisy2{record2, 13};
+    InPlaceFunction<size_t()> func2{std::move(noisy2)};
+    EXPECT_EQ(record2, Record(1, 0, 0)); // move, copy, dtor
+    EXPECT_EQ(func2(), 13ull);
+}
+
+TEST(InPlaceFunctionTests, FunctionCtorForwarding) {
+    {
+        Record record;
+        Noisy noisy{record, 17};
+        InPlaceFunction<size_t()> func{noisy};
+        EXPECT_EQ(record, Record(0, 1, 0)); // move, copy, dtor
+        EXPECT_EQ(func(), 17ull);
+        InPlaceFunction<size_t()> func2{func};
+        EXPECT_EQ(record, Record(0, 2, 0)); // move, copy, dtor
+        EXPECT_EQ(func2(), 17ull);
+    }
+    Record record;
+    Noisy noisy{record, 13};
+    InPlaceFunction<size_t()> func{noisy};
+    EXPECT_EQ(record, Record(0, 1, 0)); // move, copy, dtor
+    EXPECT_EQ(func(), 13ull);
+    InPlaceFunction<size_t()> func2{std::move(func)};
+    EXPECT_EQ(record, Record(1, 1, 0)); // move, copy, dtor
+    EXPECT_EQ(func2(), 13ull);
+    // We expect moved from functions to still be valid
+    EXPECT_TRUE(!(!func));
+    EXPECT_EQ(static_cast<bool>(func), static_cast<bool>(func2));
+    EXPECT_EQ(func(), 13ull);
+}
+
+TEST(InPlaceFunctionTests, Dtor) {
+    Record record;
+    {
+        InPlaceFunction<size_t()> func;
+        {
+            Noisy noisy{record, 17};
+            func = noisy;
+        }
+        EXPECT_EQ(func(), 17ull);
+        EXPECT_EQ(record.dtor_called, 1ull);
+    }
+    EXPECT_EQ(record.dtor_called, 2ull);
+}
+
+TEST(InPlaceFunctionTests, Assignment) {
+    {
+        Record record;
+        Record record2;
+        Noisy noisy{record, 17};
+        Noisy noisy2{record2, 5};
+        InPlaceFunction<size_t()> func{noisy};
+        EXPECT_EQ(func(), 17ull);
+        EXPECT_EQ(record.dtor_called, 0ull);
+        func = noisy2;
+        EXPECT_EQ(record.dtor_called, 1ull);
+        EXPECT_EQ(record2, Record(0, 1, 0)); // move, copy, dtor
+        EXPECT_EQ(func(), 5ull);
+    }
+    {
+        Record record;
+        Record record2;
+        Noisy noisy{record, 17};
+        Noisy noisy2{record2, 5};
+        InPlaceFunction<size_t()> func{noisy};
+        EXPECT_EQ(func(), 17ull);
+        EXPECT_EQ(record.dtor_called, 0ull);
+        func = std::move(noisy2);
+        EXPECT_EQ(record.dtor_called, 1ull);
+        EXPECT_EQ(record2, Record(1, 0, 0)); // move, copy, dtor
+        EXPECT_EQ(func(), 5ull);
+    }
+
+    {
+        Record record;
+        Record record2;
+        Noisy noisy{record, 17};
+        Noisy noisy2{record2, 13};
+        {
+            InPlaceFunction<size_t()> func{noisy};
+            EXPECT_EQ(func(), 17ull);
+            InPlaceFunction<size_t()> func2{noisy2};
+            EXPECT_EQ(record2, Record(0, 1, 0)); // move, copy, dtor
+            EXPECT_EQ(record.dtor_called, 0ull);
+            func = func2;
+            EXPECT_EQ(record.dtor_called, 1ull);
+            EXPECT_EQ(func(), 13ull);
+            EXPECT_EQ(record2, Record(0, 2, 0)); // move, copy, dtor
+            EXPECT_TRUE(static_cast<bool>(func2));
+            EXPECT_EQ(func2(), 13ull);
+        }
+        EXPECT_EQ(record2, Record(0, 2, 2)); // move, copy, dtor
+    }
+
+    {
+        Record record;
+        Record record2;
+        Noisy noisy{record, 17};
+        Noisy noisy2{record2, 13};
+        {
+            InPlaceFunction<size_t()> func{noisy};
+            EXPECT_EQ(func(), 17ull);
+            InPlaceFunction<size_t()> func2{noisy2};
+            EXPECT_EQ(record.dtor_called, 0ull);
+            EXPECT_EQ(record2, Record(0, 1, 0)); // move, copy, dtor
+            func = std::move(func2);
+            EXPECT_EQ(record.dtor_called, 1ull);
+            EXPECT_EQ(func(), 13ull);
+            EXPECT_EQ(record2, Record(1, 1, 0)); // move, copy, dtor
+            // Moved from function is still valid
+            EXPECT_TRUE(static_cast<bool>(func2));
+            EXPECT_EQ(func2(), 13ull);
+        }
+        EXPECT_EQ(record2, Record(1, 1, 2)); // move, copy, dtor
+    }
+}
+
+TEST(InPlaceFunctionTests, Swap) {
+    Record record1;
+    Record record2;
+    InPlaceFunction<size_t()> func1 = Noisy{record1, 5};
+    InPlaceFunction<size_t()> func2 = Noisy{record2, 7};
+    EXPECT_EQ(record1, Record(1, 0, 1)); // move, copy, dtor
+    EXPECT_EQ(record2, Record(1, 0, 1)); // move, copy, dtor
+    EXPECT_EQ(func1(), 5ull);
+    EXPECT_EQ(func2(), 7ull);
+    func1.swap(func2);
+    EXPECT_EQ(record1, Record(2, 0, 2)); // move, copy, dtor
+    // An additional move and destroy into the temporary object
+    EXPECT_EQ(record2, Record(3, 0, 3)); // move, copy, dtor
+    EXPECT_EQ(func1(), 7ull);
+    EXPECT_EQ(func2(), 5ull);
+}
+
+TEST(InPlaceFunctionTests, Conversion) {
+    Record record;
+    Noisy noisy{record, 15};
+    {
+        InPlaceFunction<size_t(), 16> func2 = noisy;
+        EXPECT_EQ(record, Record(0, 1, 0)); // move, copy, dtor
+        {
+            InPlaceFunction<size_t(), 32> func{func2};
+            EXPECT_EQ(record, Record(0, 2, 0)); // move, copy, dtor
+            EXPECT_EQ(func2(), func());
+        }
+        EXPECT_EQ(record, Record(0, 2, 1)); // move, copy, dtor
+    }
+    EXPECT_EQ(record, Record(0, 2, 2)); // move, copy, dtor
+}
+
+TEST(InPlaceFunctionTests, ConversionMove) {
+    Record record;
+    Noisy noisy{record, 15};
+    {
+        InPlaceFunction<size_t(), 16> func2 = noisy;
+        EXPECT_EQ(record, Record(0, 1, 0)); // move, copy, dtor
+        {
+            InPlaceFunction<size_t(), 32> func{std::move(func2)};
+            EXPECT_EQ(record, Record(1, 1, 0)); // move, copy, dtor
+            EXPECT_EQ(func2(), func());
+        }
+        EXPECT_EQ(record, Record(1, 1, 1)); // move, copy, dtor
+    }
+    EXPECT_EQ(record, Record(1, 1, 2)); // move, copy, dtor
+}
+
+TEST(InPlaceFunctionTests, ConversionAssign) {
+    Record record;
+    Noisy noisy{record, 15};
+    {
+        InPlaceFunction<size_t(), 32> func;
+        {
+            InPlaceFunction<size_t(), 16> func2 = noisy;
+            EXPECT_EQ(record, Record(0, 1, 0)); // move, copy, dtor
+            func = func2;
+            EXPECT_EQ(record, Record(0, 2, 0)); // move, copy, dtor
+            EXPECT_EQ(func2(), func());
+        }
+        EXPECT_EQ(record, Record(0, 2, 1)); // move, copy, dtor
+    }
+    EXPECT_EQ(record, Record(0, 2, 2)); // move, copy, dtor
+}
+
+TEST(InPlaceFunctionTests, ConversionAssignMove) {
+    Record record;
+    Noisy noisy{record, 15};
+    {
+        InPlaceFunction<size_t(), 32> func;
+        {
+            InPlaceFunction<size_t(), 16> func2 = noisy;
+            EXPECT_EQ(record, Record(0, 1, 0)); // move, copy, dtor
+            func = std::move(func2);
+            EXPECT_EQ(record, Record(1, 1, 0)); // move, copy, dtor
+            EXPECT_EQ(func2(), func());
+        }
+        EXPECT_EQ(record, Record(1, 1, 1)); // move, copy, dtor
+    }
+    EXPECT_EQ(record, Record(1, 1, 2)); // move, copy, dtor
+}
+
+template <class T, class U, class = void>
+struct can_assign : std::false_type {};
+
+template <class T, class U>
+struct can_assign<T, U, typename std::void_t<decltype(T().operator=(U()))>> : std::true_type {};
+
+template <class From, class To, bool Expected>
+static constexpr bool Convertible =
+        (can_assign<To, From>::value ==
+         std::is_constructible_v<To, From>)&&(std::is_constructible_v<To, From> == Expected);
+
+struct TooBig {
+    std::array<uint64_t, 5> big = {1, 2, 3, 4, 5};
+    size_t operator()() { return static_cast<size_t>(big[0] + big[1] + big[2] + big[3] + big[4]); }
+};
+static_assert(sizeof(TooBig) == 40);
+struct NotCallable {};
+struct WrongArg {
+    void operator()(NotCallable) {}
+};
+struct WrongRet {
+    NotCallable operator()(size_t) { return NotCallable{}; }
+};
+
+static_assert(Convertible<InPlaceFunction<size_t(), 32>, InPlaceFunction<size_t(), 32>, true>);
+static_assert(
+        Convertible<InPlaceFunction<size_t(size_t), 32>, InPlaceFunction<size_t(), 32>, false>);
+static_assert(Convertible<InPlaceFunction<void(), 32>, InPlaceFunction<size_t(), 32>, false>);
+static_assert(Convertible<TooBig, InPlaceFunction<size_t(), 32>, false>);
+static_assert(Convertible<TooBig, InPlaceFunction<size_t(), 40>, true>);
+static_assert(Convertible<NotCallable, InPlaceFunction<size_t(), 40>, false>);
+static_assert(Convertible<WrongArg, InPlaceFunction<void(size_t), 40>, false>);
+static_assert(Convertible<WrongRet, InPlaceFunction<size_t(size_t), 40>, false>);
+// Void returning functions are modelled by any return type
+static_assert(Convertible<WrongRet, InPlaceFunction<void(size_t), 40>, true>);
+
+// Check constructibility/assignability from smaller function types
+static_assert(Convertible<InPlaceFunction<size_t(), 32>, InPlaceFunction<size_t(), 24>, false>);
+static_assert(Convertible<InPlaceFunction<size_t(), 32>, InPlaceFunction<size_t(), 40>, true>);
+static_assert(
+        Convertible<InPlaceFunction<size_t(), 32>, InPlaceFunction<size_t(size_t), 40>, false>);
+static_assert(
+        Convertible<InPlaceFunction<size_t(), 32>, InPlaceFunction<NotCallable(), 40>, false>);