1 files changed, 275 insertions, 0 deletions
diff --git a/include/mbgl/util/unique_any.hpp b/include/mbgl/util/unique_any.hpp
new file mode 100644
index 0000000000..d488930a03
--- /dev/null
+++ b/include/mbgl/util/unique_any.hpp
@@ -0,0 +1,275 @@
+#pragma once
+
+#include <typeinfo>
+#include <type_traits>
+#include <stdexcept>
+namespace mbgl {
+namespace util {
+
+class bad_any_cast : public std::bad_cast {
+public:
+    const char* what() const noexcept override {
+        return "bad any_cast<>()";
+    }
+};
+/**
+ * A variant of `std::any` for non-copyable types.
+ *
+ * Use `unique_any` for non-copyable types (e.g. `std::unique_ptr<T>`)
+ * or to ensure that no copies are made of copyable types that are
+ * moved in.
+ *
+ * `uniqe_any` differs from `std::any` in that it does not support copy construction
+ * or copy assignment. It also does not require the contained type to be copy
+ * constructible.
+ *
+ * The `any_cast<T>()` methods work similar to `std::any_cast<T>()` except that
+ * non-copyable types may only be cast to references.
+ *
+ * Example usage:
+ *  unique_any u1(3);
+ *  auto u2 = unique_any(std::move(u1)); // u1 is moved from
+ *  int i = any_cast<int>(u2);
+ *
+ *  unique_any u2;
+ *  u2 = std::unique_ptr<int>(new int);
+ *  std::unique_ptr<int> iPtr = any_cast<std::unique_ptr<int>>(std::move(u2));
+ *
+ * Inspired by linb::any (https://github.com/thelink2012/any) and the
+ * libc++ implementation (https://github.com/llvm-mirror/libcxx).
+ */
+class unique_any final
+{
+public:
+    unique_any() = default;
+
+    //Copy constructor (deleted)
+    unique_any(const unique_any& rhs) = delete;
+
+    unique_any(unique_any&& rhs)  : vtable(rhs.vtable) {
+        if (vtable) {
+            vtable->move(std::move(rhs.storage), storage);
+        }
+        rhs.vtable = nullptr;
+    }
+
+    // Constructs with a direct-initilizated object of type ValueType
+    template <typename ValueType,
+        typename _Vt = std::decay_t<ValueType>,
+        typename = std::enable_if_t<!std::is_same<_Vt, unique_any>::value> >
+    unique_any(ValueType&& value) {
+        create(std::forward<ValueType>(value));
+    }
+
+    ~unique_any() {
+        reset();
+    }
+
+    unique_any& operator=(unique_any&& rhs)  {
+        unique_any(std::move(rhs)).swap(*this);
+        return *this;
+    }
+
+    template <class ValueType,
+        typename = std::enable_if_t<!std::is_same<std::decay_t<ValueType>, unique_any>::value> >
+    unique_any& operator=(ValueType&& rhs) {
+        unique_any(std::forward<ValueType>(rhs)).swap(*this);
+        return *this;
+    }
+
+    void reset()  {
+        if (vtable) {
+            vtable->destroy(storage);
+            vtable = nullptr;
+        }
+    }
+
+    void swap(unique_any& rhs)  {
+        if (this == &rhs) {
+            return;
+        } else {
+            unique_any tmp(std::move(rhs));
+            rhs.vtable = vtable;
+            if (rhs.vtable) {
+                rhs.vtable->move(std::move(storage), rhs.storage);
+            }
+            vtable = tmp.vtable;
+            if (vtable) {
+                vtable->move(std::move(tmp.storage), storage);
+            }
+        }
+    }
+
+    const std::type_info& type() const  {
+      return !has_value()? typeid(void) : vtable->type();
+    }
+
+    bool has_value() const  {
+        return vtable != nullptr;
+    }
+
+private:
+
+    union Storage {
+        using StackStorage = std::aligned_storage_t<3*sizeof(void*), std::alignment_of<void*>::value>;
+        Storage() = default;
+
+        void * dynamic { nullptr };
+        StackStorage stack;
+    };
+
+    template<typename T>
+    struct AllocateOnStack : std::integral_constant<bool,
+        sizeof(T) <= sizeof(Storage::stack)
+        && std::alignment_of<T>::value <= std::alignment_of<Storage::StackStorage>::value
+        && std::is_nothrow_move_constructible<T>::value> {
+    };
+
+    struct VTable {
+        virtual ~VTable() = default;
+        virtual void move(Storage&& src, Storage& dest) = 0;
+        virtual void destroy(Storage&) = 0;
+        virtual const std::type_info& type() = 0;
+    };
+  
+    template <typename ValueType>
+    struct VTableHeap : public VTable {
+        void move(Storage&& src, Storage& dest) override {
+            destroy(dest);
+            dest.dynamic = src.dynamic;
+        }
+
+        void destroy(Storage& s) override {
+            if (s.dynamic) {
+                delete reinterpret_cast<ValueType*>(s.dynamic);
+            }
+            s.dynamic = nullptr;
+        }
+
+        const std::type_info& type() override {
+            return typeid(ValueType);
+        }
+    };
+
+    template <typename ValueType>
+    struct VTableStack : public VTable {
+        void move(Storage&& src, Storage& dest) override {
+            auto srcValue = reinterpret_cast<ValueType&&>(src.stack);
+            new (static_cast<void*>(&dest.stack)) ValueType(std::move(srcValue));
+            srcValue.~ValueType();
+        }
+
+        void destroy(Storage& s) override {
+            reinterpret_cast<ValueType&>(s.stack).~ValueType();
+        }
+
+        const std::type_info& type() override {
+            return typeid(ValueType);
+        }
+    };
+
+    template <typename ValueType>
+    static VTable* vtableForType() {
+        using VTableType = std::conditional_t<AllocateOnStack<ValueType>::value, VTableStack<ValueType>, VTableHeap<ValueType> >;
+        static VTableType vtable;
+        return &vtable;
+    }
+
+    template <typename ValueType, typename _Vt>
+    std::enable_if_t<AllocateOnStack<_Vt>::value>
+    createStorage(ValueType&& value) {
+        new (static_cast<void*>(&storage.stack)) _Vt(std::forward<ValueType>(value));
+    }
+
+    template <typename ValueType, typename _Vt>
+    std::enable_if_t<!AllocateOnStack<_Vt>::value>
+    createStorage(ValueType&& value) {
+        storage.dynamic = static_cast<void*>(new _Vt(std::forward<ValueType>(value)));
+    }
+
+    template <typename ValueType>
+    void create(ValueType&& value) {
+        using _Vt = std::decay_t<ValueType>;
+        vtable = vtableForType<_Vt>();
+        createStorage<ValueType, _Vt>(std::forward<ValueType>(value));
+    }
+
+    VTable* vtable { nullptr };
+    Storage storage;
+
+protected:
+    template<class ValueType>
+    friend const ValueType* any_cast(const unique_any* operand) ;
+
+    template<class ValueType>
+    friend ValueType* any_cast(unique_any* operand) ;
+
+    template<typename ValueType, typename _Vt = std::decay_t<ValueType> >
+    ValueType* cast()
+    {
+        return reinterpret_cast<ValueType *>(
+            AllocateOnStack<_Vt>::value ? &storage.stack : storage.dynamic);
+    }
+};
+
+template<typename ValueType>
+inline const ValueType* any_cast(const unique_any* any)
+{
+    return any_cast<ValueType>(const_cast<unique_any *>(any));
+}
+
+template<typename ValueType>
+inline ValueType* any_cast(unique_any* any)
+{
+    if(any == nullptr || any->type() != typeid(ValueType))
+        return nullptr;
+    else
+        return any->cast<ValueType>();
+}
+
+template<typename ValueType, typename _Vt = std::decay_t<ValueType> >
+inline ValueType any_cast(const unique_any& any)
+{
+    static_assert(std::is_constructible<ValueType, const _Vt&>::value,
+        "any_cast type can't construct copy of contained object");
+    auto temp = any_cast<_Vt>(&any);
+    if (temp == nullptr) {
+        throw bad_any_cast();
+    }
+    return static_cast<ValueType>(*temp);
+}
+
+template<typename ValueType, typename _Vt = std::decay_t<ValueType> >
+inline ValueType any_cast(unique_any& any)
+{
+    static_assert(std::is_constructible<ValueType, const _Vt&>::value,
+        "any_cast type can't construct copy of contained object");
+    auto temp = any_cast<_Vt>(&any);
+    if (temp == nullptr) {
+        throw bad_any_cast();
+    }
+    return static_cast<ValueType>(*temp);
+}
+
+template<typename ValueType, typename _Vt = std::remove_cv_t<ValueType> >
+inline ValueType any_cast(unique_any&& any)
+{
+    auto temp = any_cast<_Vt>(&any);
+    if (temp == nullptr) {
+        throw bad_any_cast();
+    }
+    auto retValue = static_cast<ValueType>(std::move(*temp));
+    any.reset();
+    return std::move(retValue);
+}
+
+} // namespace util
+} // namespace mbgl
+
+namespace std {
+
+inline void swap(mbgl::util::unique_any& lhs, mbgl::util::unique_any& rhs)  {
+    lhs.swap(rhs);
+}
+
+} // namespace std