IVGCVSW-4519 Remove Boost Variant and apply_visitor variant

  * add mapbox/variant third party package

Signed-off-by: James Ward <james.ward@arm.com>
Change-Id: I181302780edd9dace40f158a11327316a12ce69a

9 files changed, 1718 insertions, 0 deletions

diff --git a/third-party/mapbox/LICENSE b/third-party/mapbox/LICENSE
new file mode 100644
index 0000000000..6c4ce40d5a
--- /dev/null
+++ b/third-party/mapbox/LICENSE
@@ -0,0 +1,25 @@
+Copyright (c) MapBox
+All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+- Redistributions of source code must retain the above copyright notice, this
+  list of conditions and the following disclaimer.
+- Redistributions in binary form must reproduce the above copyright notice, this
+  list of conditions and the following disclaimer in the documentation and/or
+  other materials provided with the distribution.
+- Neither the name "MapBox" nor the names of its contributors may be
+  used to endorse or promote products derived from this software without
+  specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
\ No newline at end of file
diff --git a/third-party/mapbox/LICENSE_1_0.txt b/third-party/mapbox/LICENSE_1_0.txt
new file mode 100644
index 0000000000..36b7cd93cd
--- /dev/null
+++ b/third-party/mapbox/LICENSE_1_0.txt
@@ -0,0 +1,23 @@
+Boost Software License - Version 1.0 - August 17th, 2003
+
+Permission is hereby granted, free of charge, to any person or organization
+obtaining a copy of the software and accompanying documentation covered by
+this license (the "Software") to use, reproduce, display, distribute,
+execute, and transmit the Software, and to prepare derivative works of the
+Software, and to permit third-parties to whom the Software is furnished to
+do so, all subject to the following:
+
+The copyright notices in the Software and this entire statement, including
+the above license grant, this restriction and the following disclaimer,
+must be included in all copies of the Software, in whole or in part, and
+all derivative works of the Software, unless such copies or derivative
+works are solely in the form of machine-executable object code generated by
+a source language processor.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE, TITLE AND NON-INFRINGEMENT. IN NO EVENT
+SHALL THE COPYRIGHT HOLDERS OR ANYONE DISTRIBUTING THE SOFTWARE BE LIABLE
+FOR ANY DAMAGES OR OTHER LIABILITY, WHETHER IN CONTRACT, TORT OR OTHERWISE,
+ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
diff --git a/third-party/mapbox/README.md b/third-party/mapbox/README.md
new file mode 100644
index 0000000000..6bf97f0c45
--- /dev/null
+++ b/third-party/mapbox/README.md
@@ -0,0 +1,248 @@
+# Mapbox Variant
+
+An header-only alternative to `boost::variant` for C++11 and C++14
+
+[![Build Status](https://secure.travis-ci.org/mapbox/variant.svg)](https://travis-ci.org/mapbox/variant)
+[![Build status](https://ci.appveyor.com/api/projects/status/v9tatx21j1k0fcgy)](https://ci.appveyor.com/project/Mapbox/variant)
+[![Coverage Status](https://coveralls.io/repos/mapbox/variant/badge.svg?branch=master&service=github)](https://coveralls.io/r/mapbox/variant?branch=master)
+
+## Introduction
+
+Variant's basic building blocks are:
+
+- `variant<Ts...>` - a type-safe representation for sum-types / discriminated unions
+- `recursive_wrapper<T>` - a helper type to represent recursive "tree-like" variants
+- `apply_visitor(visitor, myVariant)` - to invoke a custom visitor on the variant's underlying type
+- `get<T>()` - a function to directly unwrap a variant's underlying type
+- `.match([](Type){})` - a variant convenience member function taking an arbitrary number of lambdas creating a visitor behind the scenes and applying it to the variant
+
+### Basic Usage - HTTP API Example
+
+Suppose you want to represent a HTTP API response which is either a JSON result or an error:
+
+```c++
+struct Result {
+  Json object;
+};
+
+struct Error {
+  int32_t code;
+  string message;
+};
+```
+
+You can represent this at type level using a variant which is either an `Error` or a `Result`:
+
+```c++
+using Response = variant<Error, Result>;
+
+Response makeRequest() {
+  return Error{501, "Not Implemented"};
+}
+
+Response ret = makeRequest();
+```
+
+To see which type the `Response` holds you pattern match on the variant unwrapping the underlying value:
+
+```c++
+ret.match([] (Result r) { print(r.object); },
+          [] (Error e)  { print(e.message); });
+```
+
+Instead of using the variant's convenience `.match` pattern matching function you can create a type visitor functor and use `apply_visitor` manually:
+
+```c++
+struct ResponseVisitor {
+  void operator()(Result r) const {
+    print(r.object);
+  }
+
+  void operator()(Error e) const {
+    print(e.message);
+  }
+};
+
+ResponseVisitor visitor;
+apply_visitor(visitor, ret);
+```
+
+In both cases the compiler makes sure you handle all types the variant can represent at compile.
+
+### Recursive Variants - JSON Example
+
+[JSON](http://www.json.org/) consists of types `String`, `Number`, `True`, `False`, `Null`, `Array` and `Object`.
+
+```c++
+struct String { string value; };
+struct Number { double value; };
+struct True   { };
+struct False  { };
+struct Null   { };
+struct Array  { vector<?> values; };
+struct Object { unordered_map<string, ?> values; };
+```
+
+This works for primitive types but how do we represent recursive types such as `Array` which can hold multiple elements and `Array` itself, too?
+
+For these use cases Variant provides a `recursive_wrapper` helper type which lets you express recursive Variants.
+
+```c++
+struct String { string value; };
+struct Number { double value; };
+struct True   { };
+struct False  { };
+struct Null   { };
+
+// Forward declarations only
+struct Array;
+struct Object;
+
+using Value = variant<String, Number, True, False, Null, recursive_wrapper<Array>, recursive_wrapper<Object>>;
+
+struct Array {
+  vector<Value> values;
+};
+
+struct Object {
+  unordered_map<string, Value> values;
+};
+```
+
+For walking the JSON representation you can again either create a `JSONVisitor`:
+
+```c++
+struct JSONVisitor {
+
+  void operator()(Null) const {
+    print("null");
+  }
+
+  // same for all other JSON types
+};
+
+JSONVisitor visitor;
+apply_visitor(visitor, json);
+```
+
+Or use the convenience `.match` pattern matching function:
+
+```c++
+json.match([] (Null) { print("null"); },
+           ...);
+```
+
+To summarize: use `recursive_wrapper` to represent recursive "tree-like" representations:
+
+```c++
+struct Empty { };
+struct Node;
+
+using Tree = variant<Empty, recursive_wrapper<Node>>;
+
+struct Node {
+  uint64_t value;
+}
+```
+
+### Advanced Usage Tips
+
+Creating type aliases for variants is a great way to reduce repetition.
+Keep in mind those type aliases are not checked at type level, though.
+We recommend creating a new type for all but basic variant usage:
+
+```c++
+// the compiler can't tell the following two apart
+using APIResult = variant<Error, Result>;
+using FilesystemResult = variant<Error, Result>;
+
+// new type
+struct APIResult : variant<Error, Result> {
+  using Base = variant<Error, Result>;
+  using Base::Base;
+}
+```
+
+## Why use Mapbox Variant?
+
+Mapbox variant has the same speedy performance of `boost::variant` but is
+faster to compile, results in smaller binaries, and has no dependencies.
+
+For example on OS X 10.9 with clang++ and libc++:
+
+Test | Mapbox Variant | Boost Variant
+---- | -------------- | -------------
+Size of pre-compiled header (release / debug) | 2.8/2.8 MB         | 12/15 MB
+Size of simple program linking variant (release / debug)     | 8/24 K             | 12/40 K
+Time to compile header     | 185 ms             |  675 ms
+
+(Numbers from an older version of Mapbox variant.)
+
+## Goals
+
+Mapbox `variant` has been a very valuable, lightweight alternative for apps
+that can use c++11 or c++14 but that do not want a boost dependency.
+Mapbox `variant` has also been useful in apps that do depend on boost, like
+mapnik, to help (slightly) with compile times and to majorly lessen dependence
+on boost in core headers. The original goal and near term goal is to maintain
+external API compatibility with `boost::variant` such that Mapbox `variant`
+can be a "drop in". At the same time the goal is to stay minimal: Only
+implement the features that are actually needed in existing software. So being
+an "incomplete" implementation is just fine.
+
+Currently Mapbox variant doesn't try to be API compatible with the upcoming
+variant standard, because the standard is not finished and it would be too much
+work. But we'll revisit this decision in the future if needed.
+
+If Mapbox variant is not for you, have a look at [these other
+implementations](doc/other_implementations.md).
+
+Want to know more about the upcoming standard? Have a look at our
+[overview](doc/standards_effort.md).
+
+Most modern high-level languages provide ways to express sum types directly.
+If you're curious have a look at Haskell's pattern matching or Rust's and Swift's enums.
+
+## Depends
+
+- Compiler supporting `-std=c++11` or `-std=c++14`
+
+Tested with:
+
+- g++-4.7
+- g++-4.8
+- g++-4.9
+- g++-5.2
+- clang++-3.5
+- clang++-3.6
+- clang++-3.7
+- clang++-3.8
+- clang++-3.9
+- Visual Studio 2015
+
+## Unit Tests
+
+On Unix systems compile and run the unit tests with `make test`.
+
+On Windows run `scripts/build-local.bat`.
+
+## Limitations
+
+- The `variant` can not hold references (something like `variant<int&>` is
+  not possible). You might want to try `std::reference_wrapper` instead.
+
+## Deprecations
+
+- The included implementation of `optional` is deprecated and will be removed
+  in a future version. See [issue #64](https://github.com/mapbox/variant/issues/64).
+- Old versions of the code needed visitors to derive from `static_visitor`.
+  This is not needed any more and marked as deprecated. The `static_visitor`
+  class will be removed in future versions.
+
+## Benchmarks
+
+    make bench
+
+## Check object sizes
+
+    make sizes /path/to/boost/variant.hpp
diff --git a/third-party/mapbox/optional.hpp b/third-party/mapbox/optional.hpp
new file mode 100644
index 0000000000..d84705c1ac
--- /dev/null
+++ b/third-party/mapbox/optional.hpp
@@ -0,0 +1,74 @@
+#ifndef MAPBOX_UTIL_OPTIONAL_HPP
+#define MAPBOX_UTIL_OPTIONAL_HPP
+
+#pragma message("This implementation of optional is deprecated. See https://github.com/mapbox/variant/issues/64.")
+
+#include <type_traits>
+#include <utility>
+
+#include <mapbox/variant.hpp>
+
+namespace mapbox {
+namespace util {
+
+template <typename T>
+class optional
+{
+    static_assert(!std::is_reference<T>::value, "optional doesn't support references");
+
+    struct none_type
+    {
+    };
+
+    variant<none_type, T> variant_;
+
+public:
+    optional() = default;
+
+    optional(optional const& rhs)
+    {
+        if (this != &rhs)
+        { // protect against invalid self-assignment
+            variant_ = rhs.variant_;
+        }
+    }
+
+    optional(T const& v) { variant_ = v; }
+
+    explicit operator bool() const noexcept { return variant_.template is<T>(); }
+
+    T const& get() const { return variant_.template get<T>(); }
+    T& get() { return variant_.template get<T>(); }
+
+    T const& operator*() const { return this->get(); }
+    T operator*() { return this->get(); }
+
+    optional& operator=(T const& v)
+    {
+        variant_ = v;
+        return *this;
+    }
+
+    optional& operator=(optional const& rhs)
+    {
+        if (this != &rhs)
+        {
+            variant_ = rhs.variant_;
+        }
+        return *this;
+    }
+
+    template <typename... Args>
+    void emplace(Args&&... args)
+    {
+        variant_ = T{std::forward<Args>(args)...};
+    }
+
+    void reset() { variant_ = none_type{}; }
+
+}; // class optional
+
+} // namespace util
+} // namespace mapbox
+
+#endif // MAPBOX_UTIL_OPTIONAL_HPP
diff --git a/third-party/mapbox/recursive_wrapper.hpp b/third-party/mapbox/recursive_wrapper.hpp
new file mode 100644
index 0000000000..4ffcbd7c93
--- /dev/null
+++ b/third-party/mapbox/recursive_wrapper.hpp
@@ -0,0 +1,122 @@
+#ifndef MAPBOX_UTIL_RECURSIVE_WRAPPER_HPP
+#define MAPBOX_UTIL_RECURSIVE_WRAPPER_HPP
+
+// Based on variant/recursive_wrapper.hpp from boost.
+//
+// Original license:
+//
+// Copyright (c) 2002-2003
+// Eric Friedman, Itay Maman
+//
+// Distributed under the Boost Software License, Version 1.0. (See
+// accompanying file LICENSE_1_0.txt or copy at
+// http://www.boost.org/LICENSE_1_0.txt)
+
+#include <cassert>
+#include <utility>
+
+namespace mapbox {
+namespace util {
+
+template <typename T>
+class recursive_wrapper
+{
+
+    T* p_;
+
+    void assign(T const& rhs)
+    {
+        this->get() = rhs;
+    }
+
+public:
+    using type = T;
+
+    /**
+     * Default constructor default initializes the internally stored value.
+     * For POD types this means nothing is done and the storage is
+     * uninitialized.
+     *
+     * @throws std::bad_alloc if there is insufficient memory for an object
+     *         of type T.
+     * @throws any exception thrown by the default constructur of T.
+     */
+    recursive_wrapper()
+        : p_(new T){}
+
+    ~recursive_wrapper() noexcept { delete p_; }
+
+    recursive_wrapper(recursive_wrapper const& operand)
+        : p_(new T(operand.get())) {}
+
+    recursive_wrapper(T const& operand)
+        : p_(new T(operand)) {}
+
+    recursive_wrapper(recursive_wrapper&& operand)
+        : p_(new T(std::move(operand.get()))) {}
+
+    recursive_wrapper(T&& operand)
+        : p_(new T(std::move(operand))) {}
+
+    inline recursive_wrapper& operator=(recursive_wrapper const& rhs)
+    {
+        assign(rhs.get());
+        return *this;
+    }
+
+    inline recursive_wrapper& operator=(T const& rhs)
+    {
+        assign(rhs);
+        return *this;
+    }
+
+    inline void swap(recursive_wrapper& operand) noexcept
+    {
+        T* temp = operand.p_;
+        operand.p_ = p_;
+        p_ = temp;
+    }
+
+    recursive_wrapper& operator=(recursive_wrapper&& rhs) noexcept
+    {
+        swap(rhs);
+        return *this;
+    }
+
+    recursive_wrapper& operator=(T&& rhs)
+    {
+        get() = std::move(rhs);
+        return *this;
+    }
+
+    T& get()
+    {
+        assert(p_);
+        return *get_pointer();
+    }
+
+    T const& get() const
+    {
+        assert(p_);
+        return *get_pointer();
+    }
+
+    T* get_pointer() { return p_; }
+
+    const T* get_pointer() const { return p_; }
+
+    operator T const&() const { return this->get(); }
+
+    operator T&() { return this->get(); }
+
+}; // class recursive_wrapper
+
+template <typename T>
+inline void swap(recursive_wrapper<T>& lhs, recursive_wrapper<T>& rhs) noexcept
+{
+    lhs.swap(rhs);
+}
+} // namespace util
+} // namespace mapbox
+
+#endif // MAPBOX_UTIL_RECURSIVE_WRAPPER_HPP
diff --git a/third-party/mapbox/variant.hpp b/third-party/mapbox/variant.hpp
new file mode 100644
index 0000000000..06a46abe5d
--- /dev/null
+++ b/third-party/mapbox/variant.hpp
@@ -0,0 +1,1053 @@
+#ifndef MAPBOX_UTIL_VARIANT_HPP
+#define MAPBOX_UTIL_VARIANT_HPP
+
+#include <cassert>
+#include <cstddef>   // size_t
+#include <new>       // operator new
+#include <stdexcept> // runtime_error
+#include <string>
+#include <tuple>
+#include <type_traits>
+#include <typeinfo>
+#include <utility>
+#include <functional>
+#include <limits>
+
+#include <mapbox/recursive_wrapper.hpp>
+#include <mapbox/variant_visitor.hpp>
+
+// clang-format off
+// [[deprecated]] is only available in C++14, use this for the time being
+#if __cplusplus <= 201103L
+# ifdef __GNUC__
+#  define MAPBOX_VARIANT_DEPRECATED __attribute__((deprecated))
+# elif defined(_MSC_VER)
+#  define MAPBOX_VARIANT_DEPRECATED __declspec(deprecated)
+# else
+#  define MAPBOX_VARIANT_DEPRECATED
+# endif
+#else
+#  define MAPBOX_VARIANT_DEPRECATED [[deprecated]]
+#endif
+
+
+#ifdef _MSC_VER
+// https://msdn.microsoft.com/en-us/library/bw1hbe6y.aspx
+# ifdef NDEBUG
+#  define VARIANT_INLINE __forceinline
+# else
+#  define VARIANT_INLINE //__declspec(noinline)
+# endif
+#else
+# ifdef NDEBUG
+#  define VARIANT_INLINE //inline __attribute__((always_inline))
+# else
+#  define VARIANT_INLINE __attribute__((noinline))
+# endif
+#endif
+// clang-format on
+
+// Exceptions
+#if defined( __EXCEPTIONS) || defined( _MSC_VER)
+#define HAS_EXCEPTIONS
+#endif
+
+#define VARIANT_MAJOR_VERSION 1
+#define VARIANT_MINOR_VERSION 1
+#define VARIANT_PATCH_VERSION 0
+
+#define VARIANT_VERSION (VARIANT_MAJOR_VERSION * 100000) + (VARIANT_MINOR_VERSION * 100) + (VARIANT_PATCH_VERSION)
+
+namespace mapbox {
+namespace util {
+
+// XXX This should derive from std::logic_error instead of std::runtime_error.
+//     See https://github.com/mapbox/variant/issues/48 for details.
+class bad_variant_access : public std::runtime_error
+{
+
+public:
+    explicit bad_variant_access(const std::string& what_arg)
+        : runtime_error(what_arg) {}
+
+    explicit bad_variant_access(const char* what_arg)
+        : runtime_error(what_arg) {}
+
+}; // class bad_variant_access
+
+#if !defined(MAPBOX_VARIANT_MINIMIZE_SIZE)
+using type_index_t = unsigned int;
+#else
+#if defined(MAPBOX_VARIANT_OPTIMIZE_FOR_SPEED)
+using type_index_t = std::uint_fast8_t;
+#else
+using type_index_t = std::uint_least8_t;
+#endif
+#endif
+
+namespace detail {
+
+static constexpr type_index_t invalid_value = type_index_t(-1);
+
+template <typename T, typename... Types>
+struct direct_type;
+
+template <typename T, typename First, typename... Types>
+struct direct_type<T, First, Types...>
+{
+    static constexpr type_index_t index = std::is_same<T, First>::value
+        ? sizeof...(Types)
+        : direct_type<T, Types...>::index;
+};
+
+template <typename T>
+struct direct_type<T>
+{
+    static constexpr type_index_t index = invalid_value;
+};
+
+#if __cpp_lib_logical_traits >= 201510L
+
+using std::conjunction;
+using std::disjunction;
+
+#else
+
+template <typename...>
+struct conjunction : std::true_type {};
+
+template <typename B1>
+struct conjunction<B1> : B1 {};
+
+template <typename B1, typename B2>
+struct conjunction<B1, B2> : std::conditional<B1::value, B2, B1>::type {};
+
+template <typename B1, typename... Bs>
+struct conjunction<B1, Bs...> : std::conditional<B1::value, conjunction<Bs...>, B1>::type {};
+
+template <typename...>
+struct disjunction : std::false_type {};
+
+template <typename B1>
+struct disjunction<B1> : B1 {};
+
+template <typename B1, typename B2>
+struct disjunction<B1, B2> : std::conditional<B1::value, B1, B2>::type {};
+
+template <typename B1, typename... Bs>
+struct disjunction<B1, Bs...> : std::conditional<B1::value, B1, disjunction<Bs...>>::type {};
+
+#endif
+
+template <typename T, typename... Types>
+struct convertible_type;
+
+template <typename T, typename First, typename... Types>
+struct convertible_type<T, First, Types...>
+{
+    static constexpr type_index_t index = std::is_convertible<T, First>::value
+        ? disjunction<std::is_convertible<T, Types>...>::value ? invalid_value : sizeof...(Types)
+        : convertible_type<T, Types...>::index;
+};
+
+template <typename T>
+struct convertible_type<T>
+{
+    static constexpr type_index_t index = invalid_value;
+};
+
+template <typename T, typename... Types>
+struct value_traits
+{
+    using value_type = typename std::remove_const<typename std::remove_reference<T>::type>::type;
+    using value_type_wrapper = recursive_wrapper<value_type>;
+    static constexpr type_index_t direct_index = direct_type<value_type, Types...>::index;
+    static constexpr bool is_direct = direct_index != invalid_value;
+    static constexpr type_index_t index_direct_or_wrapper = is_direct ? direct_index : direct_type<value_type_wrapper, Types...>::index;
+    static constexpr bool is_direct_or_wrapper = index_direct_or_wrapper != invalid_value;
+    static constexpr type_index_t index = is_direct_or_wrapper ? index_direct_or_wrapper : convertible_type<value_type, Types...>::index;
+    static constexpr bool is_valid = index != invalid_value;
+    static constexpr type_index_t tindex = is_valid ? sizeof...(Types)-index : 0;
+    using target_type = typename std::tuple_element<tindex, std::tuple<void, Types...>>::type;
+};
+
+template <typename Src, typename Dest>
+struct copy_cvref
+{
+    using type = Dest;
+};
+
+template <typename Src, typename Dest>
+struct copy_cvref<Src const&, Dest>
+{
+    using type = Dest const&;
+};
+
+template <typename Src, typename Dest>
+struct copy_cvref<Src&, Dest>
+{
+    using type = Dest&;
+};
+
+template <typename Src, typename Dest>
+struct copy_cvref<Src&&, Dest>
+{
+    using type = Dest&&;
+};
+
+template <typename F, typename = void>
+struct deduced_result_type
+{};
+
+template <typename F, typename... Args>
+struct deduced_result_type<F(Args...), decltype((void)std::declval<F>()(std::declval<Args>()...))>
+{
+    using type = decltype(std::declval<F>()(std::declval<Args>()...));
+};
+
+template <typename F, typename = void>
+struct visitor_result_type : deduced_result_type<F>
+{};
+
+// specialization for explicit result_type member in visitor class
+template <typename F, typename... Args>
+struct visitor_result_type<F(Args...), decltype((void)std::declval<typename std::decay<F>::type::result_type>())>
+{
+    using type = typename std::decay<F>::type::result_type;
+};
+
+template <typename F, typename T>
+using result_of_unary_visit = typename visitor_result_type<F&&(T&&)>::type;
+
+template <typename F, typename T>
+using result_of_binary_visit = typename visitor_result_type<F&&(T&&, T&&)>::type;
+
+template <type_index_t arg1, type_index_t... others>
+struct static_max;
+
+template <type_index_t arg>
+struct static_max<arg>
+{
+    static const type_index_t value = arg;
+};
+
+template <type_index_t arg1, type_index_t arg2, type_index_t... others>
+struct static_max<arg1, arg2, others...>
+{
+    static const type_index_t value = arg1 >= arg2 ? static_max<arg1, others...>::value : static_max<arg2, others...>::value;
+};
+
+template <typename... Types>
+struct variant_helper;
+
+template <typename T, typename... Types>
+struct variant_helper<T, Types...>
+{
+    VARIANT_INLINE static void destroy(const type_index_t type_index, void* data)
+    {
+        if (type_index == sizeof...(Types))
+        {
+            reinterpret_cast<T*>(data)->~T();
+        }
+        else
+        {
+            variant_helper<Types...>::destroy(type_index, data);
+        }
+    }
+
+    VARIANT_INLINE static void move(const type_index_t old_type_index, void* old_value, void* new_value)
+    {
+        if (old_type_index == sizeof...(Types))
+        {
+            new (new_value) T(std::move(*reinterpret_cast<T*>(old_value)));
+        }
+        else
+        {
+            variant_helper<Types...>::move(old_type_index, old_value, new_value);
+        }
+    }
+
+    VARIANT_INLINE static void copy(const type_index_t old_type_index, const void* old_value, void* new_value)
+    {
+        if (old_type_index == sizeof...(Types))
+        {
+            new (new_value) T(*reinterpret_cast<const T*>(old_value));
+        }
+        else
+        {
+            variant_helper<Types...>::copy(old_type_index, old_value, new_value);
+        }
+    }
+};
+
+template <>
+struct variant_helper<>
+{
+    VARIANT_INLINE static void destroy(const type_index_t, void*) {}
+    VARIANT_INLINE static void move(const type_index_t, void*, void*) {}
+    VARIANT_INLINE static void copy(const type_index_t, const void*, void*) {}
+};
+
+template <typename T>
+struct unwrapper
+{
+    using value_type = T;
+
+    template <typename V>
+    static auto apply(typename std::remove_reference<V>::type& var)
+        -> typename std::enable_if<std::is_lvalue_reference<V>::value,
+                    decltype(var.template get_unchecked<T>())>::type
+    {
+        return var.template get_unchecked<T>();
+    }
+
+    template <typename V>
+    static auto apply(typename std::remove_reference<V>::type& var)
+        -> typename std::enable_if<!std::is_lvalue_reference<V>::value,
+                    decltype(std::move(var.template get_unchecked<T>()))>::type
+    {
+        return std::move(var.template get_unchecked<T>());
+    }
+};
+
+template <typename T>
+struct unwrapper<recursive_wrapper<T>> : unwrapper<T>
+{};
+
+template <typename T>
+struct unwrapper<std::reference_wrapper<T>> : unwrapper<T>
+{};
+
+template <typename R, typename... Types>
+struct dispatcher;
+
+template <typename R, typename T, typename... Types>
+struct dispatcher<R, T, Types...>
+{
+    template <typename V, typename F>
+    VARIANT_INLINE static R apply(V&& v, F&& f)
+    {
+        if (v.template is<T>())
+        {
+            return std::forward<F>(f)(unwrapper<T>::template apply<V>(v));
+        }
+        else
+        {
+            return dispatcher<R, Types...>::apply(std::forward<V>(v), std::forward<F>(f));
+        }
+    }
+};
+
+template <typename R, typename T>
+struct dispatcher<R, T>
+{
+    template <typename V, typename F>
+    VARIANT_INLINE static R apply(V&& v, F&& f)
+    {
+        return std::forward<F>(f)(unwrapper<T>::template apply<V>(v));
+    }
+};
+
+template <typename R, typename T, typename... Types>
+struct binary_dispatcher_rhs;
+
+template <typename R, typename T0, typename T1, typename... Types>
+struct binary_dispatcher_rhs<R, T0, T1, Types...>
+{
+    template <typename V, typename F>
+    VARIANT_INLINE static R apply(V&& lhs, V&& rhs, F&& f)
+    {
+        if (rhs.template is<T1>()) // call binary functor
+        {
+            return std::forward<F>(f)(unwrapper<T0>::template apply<V>(lhs),
+                                      unwrapper<T1>::template apply<V>(rhs));
+        }
+        else
+        {
+            return binary_dispatcher_rhs<R, T0, Types...>::apply(std::forward<V>(lhs),
+                                                                 std::forward<V>(rhs),
+                                                                 std::forward<F>(f));
+        }
+    }
+};
+
+template <typename R, typename T0, typename T1>
+struct binary_dispatcher_rhs<R, T0, T1>
+{
+    template <typename V, typename F>
+    VARIANT_INLINE static R apply(V&& lhs, V&& rhs, F&& f)
+    {
+        return std::forward<F>(f)(unwrapper<T0>::template apply<V>(lhs),
+                                  unwrapper<T1>::template apply<V>(rhs));
+    }
+};
+
+template <typename R, typename T, typename... Types>
+struct binary_dispatcher_lhs;
+
+template <typename R, typename T0, typename T1, typename... Types>
+struct binary_dispatcher_lhs<R, T0, T1, Types...>
+{
+    template <typename V, typename F>
+    VARIANT_INLINE static R apply(V&& lhs, V&& rhs, F&& f)
+    {
+        if (lhs.template is<T1>()) // call binary functor
+        {
+            return std::forward<F>(f)(unwrapper<T1>::template apply<V>(lhs),
+                                      unwrapper<T0>::template apply<V>(rhs));
+        }
+        else
+        {
+            return binary_dispatcher_lhs<R, T0, Types...>::apply(std::forward<V>(lhs),
+                                                                 std::forward<V>(rhs),
+                                                                 std::forward<F>(f));
+        }
+    }
+};
+
+template <typename R, typename T0, typename T1>
+struct binary_dispatcher_lhs<R, T0, T1>
+{
+    template <typename V, typename F>
+    VARIANT_INLINE static R apply(V&& lhs, V&& rhs, F&& f)
+    {
+        return std::forward<F>(f)(unwrapper<T1>::template apply<V>(lhs),
+                                  unwrapper<T0>::template apply<V>(rhs));
+    }
+};
+
+template <typename R, typename... Types>
+struct binary_dispatcher;
+
+template <typename R, typename T, typename... Types>
+struct binary_dispatcher<R, T, Types...>
+{
+    template <typename V, typename F>
+    VARIANT_INLINE static R apply(V&& v0, V&& v1, F&& f)
+    {
+        if (v0.template is<T>())
+        {
+            if (v1.template is<T>())
+            {
+                return std::forward<F>(f)(unwrapper<T>::template apply<V>(v0),
+                                          unwrapper<T>::template apply<V>(v1)); // call binary functor
+            }
+            else
+            {
+                return binary_dispatcher_rhs<R, T, Types...>::apply(std::forward<V>(v0),
+                                                                    std::forward<V>(v1),
+                                                                    std::forward<F>(f));
+            }
+        }
+        else if (v1.template is<T>())
+        {
+            return binary_dispatcher_lhs<R, T, Types...>::apply(std::forward<V>(v0),
+                                                                std::forward<V>(v1),
+                                                                std::forward<F>(f));
+        }
+        return binary_dispatcher<R, Types...>::apply(std::forward<V>(v0),
+                                                     std::forward<V>(v1),
+                                                     std::forward<F>(f));
+    }
+};
+
+template <typename R, typename T>
+struct binary_dispatcher<R, T>
+{
+    template <typename V, typename F>
+    VARIANT_INLINE static R apply(V&& v0, V&& v1, F&& f)
+    {
+        return std::forward<F>(f)(unwrapper<T>::template apply<V>(v0),
+                                  unwrapper<T>::template apply<V>(v1)); // call binary functor
+    }
+};
+
+// comparator functors
+struct equal_comp
+{
+    template <typename T>
+    bool operator()(T const& lhs, T const& rhs) const
+    {
+        return lhs == rhs;
+    }
+};
+
+struct less_comp
+{
+    template <typename T>
+    bool operator()(T const& lhs, T const& rhs) const
+    {
+        return lhs < rhs;
+    }
+};
+
+template <typename Variant, typename Comp>
+class comparer
+{
+public:
+    explicit comparer(Variant const& lhs) noexcept
+        : lhs_(lhs) {}
+    comparer& operator=(comparer const&) = delete;
+    // visitor
+    template <typename T>
+    bool operator()(T const& rhs_content) const
+    {
+        T const& lhs_content = lhs_.template get_unchecked<T>();
+        return Comp()(lhs_content, rhs_content);
+    }
+
+private:
+    Variant const& lhs_;
+};
+
+// hashing visitor
+struct hasher
+{
+    template <typename T>
+    std::size_t operator()(const T& hashable) const
+    {
+        return std::hash<T>{}(hashable);
+    }
+};
+
+} // namespace detail
+
+struct no_init {};
+
+template <typename... Types>
+class variant
+{
+    static_assert(sizeof...(Types) > 0, "Template parameter type list of variant can not be empty.");
+    static_assert(!detail::disjunction<std::is_reference<Types>...>::value, "Variant can not hold reference types. Maybe use std::reference_wrapper?");
+    static_assert(!detail::disjunction<std::is_array<Types>...>::value, "Variant can not hold array types.");
+    static_assert(sizeof...(Types) < std::numeric_limits<type_index_t>::max(), "Internal index type must be able to accommodate all alternatives.");
+private:
+    static const std::size_t data_size = detail::static_max<sizeof(Types)...>::value;
+    static const std::size_t data_align = detail::static_max<alignof(Types)...>::value;
+public:
+    struct adapted_variant_tag;
+    using types = std::tuple<Types...>;
+private:
+    using first_type = typename std::tuple_element<0, types>::type;
+    using unwrap_first_type = typename detail::unwrapper<first_type>::value_type;
+    using data_type = typename std::aligned_storage<data_size, data_align>::type;
+    using helper_type = detail::variant_helper<Types...>;
+
+    template <typename V, typename T = unwrap_first_type>
+        using alternative_ref = typename detail::copy_cvref<V, T>::type;
+
+    type_index_t type_index;
+#ifdef __clang_analyzer__
+    data_type data {};
+#else
+    data_type data;
+#endif
+
+public:
+    VARIANT_INLINE variant() noexcept(std::is_nothrow_default_constructible<first_type>::value)
+        : type_index(sizeof...(Types)-1)
+    {
+        static_assert(std::is_default_constructible<first_type>::value, "First type in variant must be default constructible to allow default construction of variant.");
+        new (&data) first_type();
+    }
+
+    VARIANT_INLINE variant(no_init) noexcept
+        : type_index(detail::invalid_value) {}
+
+    // http://isocpp.org/blog/2012/11/universal-references-in-c11-scott-meyers
+    template <typename T, typename Traits = detail::value_traits<T, Types...>,
+              typename Enable = typename std::enable_if<Traits::is_valid && !std::is_same<variant<Types...>, typename Traits::value_type>::value>::type >
+    VARIANT_INLINE variant(T&& val) noexcept(std::is_nothrow_constructible<typename Traits::target_type, T&&>::value)
+        : type_index(Traits::index)
+    {
+        new (&data) typename Traits::target_type(std::forward<T>(val));
+    }
+
+    VARIANT_INLINE variant(variant<Types...> const& old)
+        : type_index(old.type_index)
+    {
+        helper_type::copy(old.type_index, &old.data, &data);
+    }
+
+    VARIANT_INLINE variant(variant<Types...>&& old)
+        noexcept(detail::conjunction<std::is_nothrow_move_constructible<Types>...>::value)
+        : type_index(old.type_index)
+    {
+        helper_type::move(old.type_index, &old.data, &data);
+    }
+
+private:
+    VARIANT_INLINE void copy_assign(variant<Types...> const& rhs)
+    {
+        helper_type::destroy(type_index, &data);
+        type_index = detail::invalid_value;
+        helper_type::copy(rhs.type_index, &rhs.data, &data);
+        type_index = rhs.type_index;
+    }
+
+    VARIANT_INLINE void move_assign(variant<Types...>&& rhs)
+    {
+        helper_type::destroy(type_index, &data);
+        type_index = detail::invalid_value;
+        helper_type::move(rhs.type_index, &rhs.data, &data);
+        type_index = rhs.type_index;
+    }
+
+public:
+    VARIANT_INLINE variant<Types...>& operator=(variant<Types...>&& other)
+        // note we check for nothrow-constructible, not nothrow-assignable, since
+        // move_assign uses move-construction via placement new.
+        noexcept(detail::conjunction<std::is_nothrow_move_constructible<Types>...>::value)
+    {
+        if (this == &other) { // playing safe in release mode, hit assertion in debug.
+            assert(false);
+            return *this;
+        }
+        move_assign(std::move(other));
+        return *this;
+    }
+
+    VARIANT_INLINE variant<Types...>& operator=(variant<Types...> const& other)
+    {
+        if (this != &other)
+            copy_assign(other);
+        return *this;
+    }
+
+    // conversions
+    // move-assign
+    template <typename T, typename Traits = detail::value_traits<T, Types...>,
+              typename Enable = typename std::enable_if<Traits::is_valid && !std::is_same<variant<Types...>, typename Traits::value_type>::value>::type >
+    VARIANT_INLINE variant<Types...>& operator=(T&& rhs)
+        // not that we check is_nothrow_constructible<T>, not is_nothrow_move_assignable<T>,
+        // since we construct a temporary
+        noexcept(std::is_nothrow_constructible<typename Traits::target_type, T&&>::value
+                 && std::is_nothrow_move_assignable<variant<Types...>>::value)
+    {
+        variant<Types...> temp(std::forward<T>(rhs));
+        move_assign(std::move(temp));
+        return *this;
+    }
+
+    // copy-assign
+    template <typename T>
+    VARIANT_INLINE variant<Types...>& operator=(T const& rhs)
+    {
+        variant<Types...> temp(rhs);
+        copy_assign(temp);
+        return *this;
+    }
+
+    template <typename T, typename std::enable_if<
+                          (detail::direct_type<T, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE bool is() const
+    {
+        return type_index == detail::direct_type<T, Types...>::index;
+    }
+
+    template <typename T,typename std::enable_if<
+                         (detail::direct_type<recursive_wrapper<T>, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE bool is() const
+    {
+        return type_index == detail::direct_type<recursive_wrapper<T>, Types...>::index;
+    }
+
+    VARIANT_INLINE bool valid() const
+    {
+        return type_index != detail::invalid_value;
+    }
+
+    template <typename T, typename... Args>
+    VARIANT_INLINE void set(Args&&... args)
+    {
+        helper_type::destroy(type_index, &data);
+        type_index = detail::invalid_value;
+        new (&data) T(std::forward<Args>(args)...);
+        type_index = detail::direct_type<T, Types...>::index;
+    }
+
+    // get_unchecked<T>()
+    template <typename T, typename std::enable_if<
+                          (detail::direct_type<T, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE T& get_unchecked()
+    {
+        return *reinterpret_cast<T*>(&data);
+    }
+
+#ifdef HAS_EXCEPTIONS
+    // get<T>()
+    template <typename T, typename std::enable_if<
+                          (detail::direct_type<T, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE T& get()
+    {
+        if (type_index == detail::direct_type<T, Types...>::index)
+        {
+            return *reinterpret_cast<T*>(&data);
+        }
+        else
+        {
+            throw bad_variant_access("in get<T>()");
+        }
+    }
+#endif
+
+    template <typename T, typename std::enable_if<
+                          (detail::direct_type<T, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE T const& get_unchecked() const
+    {
+        return *reinterpret_cast<T const*>(&data);
+    }
+
+#ifdef HAS_EXCEPTIONS
+    template <typename T, typename std::enable_if<
+                          (detail::direct_type<T, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE T const& get() const
+    {
+        if (type_index == detail::direct_type<T, Types...>::index)
+        {
+            return *reinterpret_cast<T const*>(&data);
+        }
+        else
+        {
+            throw bad_variant_access("in get<T>()");
+        }
+    }
+#endif
+
+    // get_unchecked<T>() - T stored as recursive_wrapper<T>
+    template <typename T, typename std::enable_if<
+                          (detail::direct_type<recursive_wrapper<T>, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE T& get_unchecked()
+    {
+        return (*reinterpret_cast<recursive_wrapper<T>*>(&data)).get();
+    }
+
+#ifdef HAS_EXCEPTIONS
+    // get<T>() - T stored as recursive_wrapper<T>
+    template <typename T, typename std::enable_if<
+                          (detail::direct_type<recursive_wrapper<T>, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE T& get()
+    {
+        if (type_index == detail::direct_type<recursive_wrapper<T>, Types...>::index)
+        {
+            return (*reinterpret_cast<recursive_wrapper<T>*>(&data)).get();
+        }
+        else
+        {
+            throw bad_variant_access("in get<T>()");
+        }
+    }
+#endif
+
+    template <typename T, typename std::enable_if<
+                          (detail::direct_type<recursive_wrapper<T>, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE T const& get_unchecked() const
+    {
+        return (*reinterpret_cast<recursive_wrapper<T> const*>(&data)).get();
+    }
+
+#ifdef HAS_EXCEPTIONS
+    template <typename T, typename std::enable_if<
+                          (detail::direct_type<recursive_wrapper<T>, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE T const& get() const
+    {
+        if (type_index == detail::direct_type<recursive_wrapper<T>, Types...>::index)
+        {
+            return (*reinterpret_cast<recursive_wrapper<T> const*>(&data)).get();
+        }
+        else
+        {
+            throw bad_variant_access("in get<T>()");
+        }
+    }
+#endif
+
+    // get_unchecked<T>() - T stored as std::reference_wrapper<T>
+    template <typename T, typename std::enable_if<
+                          (detail::direct_type<std::reference_wrapper<T>, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE T& get_unchecked()
+    {
+        return (*reinterpret_cast<std::reference_wrapper<T>*>(&data)).get();
+    }
+
+#ifdef HAS_EXCEPTIONS
+    // get<T>() - T stored as std::reference_wrapper<T>
+    template <typename T, typename std::enable_if<
+                          (detail::direct_type<std::reference_wrapper<T>, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE T& get()
+    {
+        if (type_index == detail::direct_type<std::reference_wrapper<T>, Types...>::index)
+        {
+            return (*reinterpret_cast<std::reference_wrapper<T>*>(&data)).get();
+        }
+        else
+        {
+            throw bad_variant_access("in get<T>()");
+        }
+    }
+#endif
+
+    template <typename T, typename std::enable_if<
+                          (detail::direct_type<std::reference_wrapper<T const>, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE T const& get_unchecked() const
+    {
+        return (*reinterpret_cast<std::reference_wrapper<T const> const*>(&data)).get();
+    }
+
+#ifdef HAS_EXCEPTIONS
+    template <typename T, typename std::enable_if<
+                          (detail::direct_type<std::reference_wrapper<T const>, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE T const& get() const
+    {
+        if (type_index == detail::direct_type<std::reference_wrapper<T const>, Types...>::index)
+        {
+            return (*reinterpret_cast<std::reference_wrapper<T const> const*>(&data)).get();
+        }
+        else
+        {
+            throw bad_variant_access("in get<T>()");
+        }
+    }
+#endif
+
+    // This function is deprecated because it returns an internal index field.
+    // Use which() instead.
+    MAPBOX_VARIANT_DEPRECATED VARIANT_INLINE type_index_t get_type_index() const
+    {
+        return type_index;
+    }
+
+    VARIANT_INLINE int which() const noexcept
+    {
+        return static_cast<int>(sizeof...(Types) - type_index - 1);
+    }
+
+    template <typename T, typename std::enable_if<
+                          (detail::direct_type<T, Types...>::index != detail::invalid_value)>::type* = nullptr>
+    VARIANT_INLINE static constexpr int which() noexcept
+    {
+        return static_cast<int>(sizeof...(Types)-detail::direct_type<T, Types...>::index - 1);
+    }
+
+    // visitor
+    // unary
+    template <typename F, typename V, typename T0 = alternative_ref<V>,
+              typename R = detail::result_of_unary_visit<F, T0>>
+    VARIANT_INLINE static R visit(V&& v, F&& f)
+    {
+        return detail::dispatcher<R, Types...>::apply(std::forward<V>(v), std::forward<F>(f));
+    }
+
+    // binary
+    template <typename F, typename V, typename T0 = alternative_ref<V>,
+              typename R = detail::result_of_binary_visit<F, T0>>
+    VARIANT_INLINE static R binary_visit(V&& v0, V&& v1, F&& f)
+    {
+        return detail::binary_dispatcher<R, Types...>::apply(std::forward<V>(v0),
+                                                             std::forward<V>(v1),
+                                                             std::forward<F>(f));
+    }
+
+    // match
+    // unary
+    template <typename... Fs>
+    auto VARIANT_INLINE match(Fs&&... fs) const&
+        -> decltype(variant::visit(*this, ::mapbox::util::make_visitor(std::forward<Fs>(fs)...)))
+    {
+        return variant::visit(*this, ::mapbox::util::make_visitor(std::forward<Fs>(fs)...));
+    }
+    // non-const
+    template <typename... Fs>
+    auto VARIANT_INLINE match(Fs&&... fs) &
+        -> decltype(variant::visit(*this, ::mapbox::util::make_visitor(std::forward<Fs>(fs)...)))
+    {
+        return variant::visit(*this, ::mapbox::util::make_visitor(std::forward<Fs>(fs)...));
+    }
+    template <typename... Fs>
+    auto VARIANT_INLINE match(Fs&&... fs) &&
+        -> decltype(variant::visit(std::move(*this), ::mapbox::util::make_visitor(std::forward<Fs>(fs)...)))
+    {
+        return variant::visit(std::move(*this), ::mapbox::util::make_visitor(std::forward<Fs>(fs)...));
+    }
+
+    ~variant() noexcept // no-throw destructor
+    {
+        helper_type::destroy(type_index, &data);
+    }
+
+    // comparison operators
+    // equality
+    VARIANT_INLINE bool operator==(variant const& rhs) const
+    {
+        assert(valid() && rhs.valid());
+        if (this->which() != rhs.which())
+        {
+            return false;
+        }
+        detail::comparer<variant, detail::equal_comp> visitor(*this);
+        return visit(rhs, visitor);
+    }
+
+    VARIANT_INLINE bool operator!=(variant const& rhs) const
+    {
+        return !(*this == rhs);
+    }
+
+    // less than
+    VARIANT_INLINE bool operator<(variant const& rhs) const
+    {
+        assert(valid() && rhs.valid());
+        if (this->which() != rhs.which())
+        {
+            return this->which() < rhs.which();
+        }
+        detail::comparer<variant, detail::less_comp> visitor(*this);
+        return visit(rhs, visitor);
+    }
+    VARIANT_INLINE bool operator>(variant const& rhs) const
+    {
+        return rhs < *this;
+    }
+    VARIANT_INLINE bool operator<=(variant const& rhs) const
+    {
+        return !(*this > rhs);
+    }
+    VARIANT_INLINE bool operator>=(variant const& rhs) const
+    {
+        return !(*this < rhs);
+    }
+};
+
+// unary visitor interface
+template <typename F, typename V>
+auto VARIANT_INLINE apply_visitor(F&& f, V&& v)
+    -> decltype(v.visit(std::forward<V>(v), std::forward<F>(f)))
+{
+    return v.visit(std::forward<V>(v), std::forward<F>(f));
+}
+
+// binary visitor interface
+template <typename F, typename V>
+auto VARIANT_INLINE apply_visitor(F&& f, V&& v0, V&& v1)
+    -> decltype(v0.binary_visit(std::forward<V>(v0), std::forward<V>(v1), std::forward<F>(f)))
+{
+    return v0.binary_visit(std::forward<V>(v0), std::forward<V>(v1), std::forward<F>(f));
+}
+
+// getter interface
+
+#ifdef HAS_EXCEPTIONS
+template <typename ResultType, typename T>
+auto get(T& var)->decltype(var.template get<ResultType>())
+{
+    return var.template get<ResultType>();
+}
+#endif
+
+template <typename ResultType, typename T>
+ResultType& get_unchecked(T& var)
+{
+    return var.template get_unchecked<ResultType>();
+}
+
+#ifdef HAS_EXCEPTIONS
+template <typename ResultType, typename T>
+auto get(T const& var)->decltype(var.template get<ResultType>())
+{
+    return var.template get<ResultType>();
+}
+#endif
+
+template <typename ResultType, typename T>
+ResultType const& get_unchecked(T const& var)
+{
+    return var.template get_unchecked<ResultType>();
+}
+// variant_size
+template <typename T>
+struct variant_size;
+
+//variable templates is c++14
+//template <typename T>
+//constexpr std::size_t variant_size_v = variant_size<T>::value;
+
+template <typename T>
+struct variant_size<const T>
+    : variant_size<T> {};
+
+template <typename T>
+struct variant_size<volatile T>
+    : variant_size<T> {};
+
+template <typename T>
+struct variant_size<const volatile T>
+    : variant_size<T> {};
+
+template <typename... Types>
+struct variant_size<variant<Types...>>
+    : std::integral_constant<std::size_t, sizeof...(Types)> {};
+
+// variant_alternative
+template <std::size_t Index, typename T>
+struct variant_alternative;
+
+#if defined(__clang__)
+#if __has_builtin(__type_pack_element)
+#define has_type_pack_element
+#endif
+#endif
+
+#if defined(has_type_pack_element)
+template <std::size_t Index, typename ...Types>
+struct variant_alternative<Index, variant<Types...>>
+{
+    static_assert(sizeof...(Types) > Index , "Index out of range");
+    using type = __type_pack_element<Index, Types...>;
+};
+#else
+template <std::size_t Index, typename First, typename...Types>
+struct variant_alternative<Index, variant<First, Types...>>
+    : variant_alternative<Index - 1, variant<Types...>>
+{
+    static_assert(sizeof...(Types) > Index -1 , "Index out of range");
+};
+
+template <typename First, typename...Types>
+struct variant_alternative<0, variant<First, Types...>>
+{
+    using type = First;
+};
+
+#endif
+
+template <size_t Index, typename T>
+using variant_alternative_t = typename variant_alternative<Index, T>::type;
+
+template <size_t Index, typename T>
+struct variant_alternative<Index, const T>
+    : std::add_const<variant_alternative<Index, T>> {};
+
+template <size_t Index, typename T>
+struct variant_alternative<Index, volatile T>
+    : std::add_volatile<variant_alternative<Index, T>> {};
+
+template <size_t Index, typename T>
+struct variant_alternative<Index, const volatile T>
+    : std::add_cv<variant_alternative<Index, T>> {};
+
+} // namespace util
+} // namespace mapbox
+
+// hashable iff underlying types are hashable
+namespace std {
+template <typename... Types>
+struct hash< ::mapbox::util::variant<Types...>> {
+    std::size_t operator()(const ::mapbox::util::variant<Types...>& v) const noexcept
+    {
+        return ::mapbox::util::apply_visitor(::mapbox::util::detail::hasher{}, v);
+    }
+};
+
+}
+
+#endif // MAPBOX_UTIL_VARIANT_HPP
diff --git a/third-party/mapbox/variant_cast.hpp b/third-party/mapbox/variant_cast.hpp
new file mode 100644
index 0000000000..fe1ab35432
--- /dev/null
+++ b/third-party/mapbox/variant_cast.hpp
@@ -0,0 +1,85 @@
+#ifndef VARIANT_CAST_HPP
+#define VARIANT_CAST_HPP
+
+#include <type_traits>
+
+namespace mapbox {
+namespace util {
+
+namespace detail {
+
+template <class T>
+class static_caster
+{
+public:
+    template <class V>
+    T& operator()(V& v) const
+    {
+        return static_cast<T&>(v);
+    }
+};
+
+template <class T>
+class dynamic_caster
+{
+public:
+    using result_type = T&;
+    template <class V>
+    T& operator()(V& v, typename std::enable_if<!std::is_polymorphic<V>::value>::type* = nullptr) const
+    {
+        throw std::bad_cast();
+    }
+    template <class V>
+    T& operator()(V& v, typename std::enable_if<std::is_polymorphic<V>::value>::type* = nullptr) const
+    {
+        return dynamic_cast<T&>(v);
+    }
+};
+
+template <class T>
+class dynamic_caster<T*>
+{
+public:
+    using result_type = T*;
+    template <class V>
+    T* operator()(V& v, typename std::enable_if<!std::is_polymorphic<V>::value>::type* = nullptr) const
+    {
+        return nullptr;
+    }
+    template <class V>
+    T* operator()(V& v, typename std::enable_if<std::is_polymorphic<V>::value>::type* = nullptr) const
+    {
+        return dynamic_cast<T*>(&v);
+    }
+};
+}
+
+template <class T, class V>
+typename detail::dynamic_caster<T>::result_type
+dynamic_variant_cast(V& v)
+{
+    return mapbox::util::apply_visitor(detail::dynamic_caster<T>(), v);
+}
+
+template <class T, class V>
+typename detail::dynamic_caster<const T>::result_type
+dynamic_variant_cast(const V& v)
+{
+    return mapbox::util::apply_visitor(detail::dynamic_caster<const T>(), v);
+}
+
+template <class T, class V>
+T& static_variant_cast(V& v)
+{
+    return mapbox::util::apply_visitor(detail::static_caster<T>(), v);
+}
+
+template <class T, class V>
+const T& static_variant_cast(const V& v)
+{
+    return mapbox::util::apply_visitor(detail::static_caster<const T>(), v);
+}
+}
+}
+
+#endif // VARIANT_CAST_HPP
diff --git a/third-party/mapbox/variant_io.hpp b/third-party/mapbox/variant_io.hpp
new file mode 100644
index 0000000000..1456cc5abc
--- /dev/null
+++ b/third-party/mapbox/variant_io.hpp
@@ -0,0 +1,45 @@
+#ifndef MAPBOX_UTIL_VARIANT_IO_HPP
+#define MAPBOX_UTIL_VARIANT_IO_HPP
+
+#include <iosfwd>
+
+#include <mapbox/variant.hpp>
+
+namespace mapbox {
+namespace util {
+
+namespace detail {
+// operator<< helper
+template <typename Out>
+class printer
+{
+public:
+    explicit printer(Out& out)
+        : out_(out) {}
+    printer& operator=(printer const&) = delete;
+
+    // visitor
+    template <typename T>
+    void operator()(T const& operand) const
+    {
+        out_ << operand;
+    }
+
+private:
+    Out& out_;
+};
+}
+
+// operator<<
+template <typename CharT, typename Traits, typename... Types>
+VARIANT_INLINE std::basic_ostream<CharT, Traits>&
+operator<<(std::basic_ostream<CharT, Traits>& out, variant<Types...> const& rhs)
+{
+    detail::printer<std::basic_ostream<CharT, Traits>> visitor(out);
+    apply_visitor(visitor, rhs);
+    return out;
+}
+} // namespace util
+} // namespace mapbox
+
+#endif // MAPBOX_UTIL_VARIANT_IO_HPP
diff --git a/third-party/mapbox/variant_visitor.hpp b/third-party/mapbox/variant_visitor.hpp
new file mode 100644
index 0000000000..54ddba0e1c
--- /dev/null
+++ b/third-party/mapbox/variant_visitor.hpp
@@ -0,0 +1,43 @@
+#ifndef MAPBOX_UTIL_VARIANT_VISITOR_HPP
+#define MAPBOX_UTIL_VARIANT_VISITOR_HPP
+
+#include <utility>
+
+namespace mapbox {
+namespace util {
+
+template <typename... Fns>
+struct visitor;
+
+template <typename Fn>
+struct visitor<Fn> : Fn
+{
+    using Fn::operator();
+
+    template<typename T>
+    visitor(T&& fn) : Fn(std::forward<T>(fn)) {}    
+};
+
+template <typename Fn, typename... Fns>
+struct visitor<Fn, Fns...> : Fn, visitor<Fns...>
+{
+    using Fn::operator();
+    using visitor<Fns...>::operator();
+
+    template<typename T, typename... Ts>
+    visitor(T&& fn, Ts&&... fns)
+        : Fn(std::forward<T>(fn))
+        , visitor<Fns...>(std::forward<Ts>(fns)...) {}
+};
+
+template <typename... Fns>
+visitor<typename std::decay<Fns>::type...> make_visitor(Fns&&... fns)
+{
+    return visitor<typename std::decay<Fns>::type...>
+        (std::forward<Fns>(fns)...);
+}
+    
+} // namespace util
+} // namespace mapbox
+
+#endif // MAPBOX_UTIL_VARIANT_VISITOR_HPP