MPark.Variant

C++17 std::variant for C++11/14/17

Introduction

MPark.Variant is an implementation of C++17 std::variant for C++11/14/17.

• Based on my implementation of std::variant for libc++
• Continuously tested against libc++'s std::variant test suite.

Documentation

• cppreference.com
• eel.is/c++draft

Integration

Single Header

The single-header branch provides a standalone variant.hpp file for each release. Copy it and #include away!

Submodule

You can add mpark/variant as a submodule to your project.

git submodule add https://github.com/mpark/variant.git 3rdparty/variant

Add the include directory to your include path with -I3rdparty/variant/include then #include the variant.hpp header with #include <mpark/variant.hpp>.

If you use CMake, you can simply use add_subdirectory(3rdparty/variant):

cmake_minimum_required(VERSION 3.6.3)

project(HelloWorld CXX)

set(CMAKE_CXX_STANDARD 14)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

add_subdirectory(3rdparty/variant)

add_executable(hello-world hello_world.cpp)
target_link_libraries(hello-world mpark_variant)

Installation / CMake find_package

git clone https://github.com/mpark/variant.git
mkdir variant/build && cd variant/build
cmake ..
cmake --build . --target install

This will install mpark/variant to the default install-directory for your platform (/usr/local for Unix, C:\Program Files for Windows). You can also install at a custom location via the CMAKE_INSTALL_PREFIX variable, (e.g., cmake .. -DCMAKE_INSTALL_PREFIX=/opt).

The installed mpark/variant can then be found by CMake via find_package:

cmake_minimum_required(VERSION 3.6.3)

project(HelloWorld CXX)

set(CMAKE_CXX_STANDARD 14)
set(CMAKE_CXX_STANDARD_REQUIRED ON)
set(CMAKE_CXX_EXTENSIONS OFF)

find_package(mpark_variant 1.2.0 REQUIRED)

add_executable(hello-world hello_world.cpp)
target_link_libraries(hello-world mpark_variant)

CMake will search for mpark/variant in its default set of installation prefixes. If mpark/variant is installed in a custom location via the CMAKE_INSTALL_PREFIX variable, you'll likely need to use the CMAKE_PREFIX_PATH to specify the location (e.g., cmake .. -DCMAKE_PREFIX_PATH=/opt).

Requirements

This library requires a standard conformant C++11 compiler. The following compilers are continously tested:

Compiler	Operating System	Version String
GCC 4.9.4	Ubuntu 14.04.5 LTS	g++-4.9 (Ubuntu 4.9.4-2ubuntu1~14.04.1) 4.9.4
GCC 5.4.1	Ubuntu 14.04.5 LTS	g++-5 (Ubuntu 5.4.1-2ubuntu1~14.04) 5.4.1 20160904
GCC 6.3.0	Ubuntu 14.04.5 LTS	g++-6 (Ubuntu/Linaro 6.3.0-18ubuntu2~14.04) 6.3.0 20170519
GCC 7.2.0	Ubuntu 14.04.5 LTS	g++-7 (Ubuntu 7.2.0-1ubuntu1~14.04) 7.2.0
Clang 3.5.0	Ubuntu 12.04.5 LTS	Ubuntu clang version 3.5.0-svn217304-1~exp1 (branches/release_35) (based on LLVM 3.5.0)
Clang 3.6.2	Ubuntu 12.04.5 LTS	Ubuntu clang version 3.6.2-svn240577-1~exp1 (branches/release_36) (based on LLVM 3.6.2)
Clang 3.7.1	Ubuntu 12.04.5 LTS	Ubuntu clang version 3.7.1-svn253571-1~exp1 (branches/release_37) (based on LLVM 3.7.1)
Clang 3.8.1	Ubuntu 12.04.5 LTS	clang version 3.8.1-svn271772-1~exp1 (branches/release_38)
Clang 3.9.1	Ubuntu 14.04.5 LTS	clang version 3.9.1-4ubuntu3~14.04.2 (tags/RELEASE_391/rc2)
Clang 4.0.1	Ubuntu 14.04.5 LTS	clang version 4.0.1-svn305264-1~exp1 (branches/release_40)
Clang 5.0.0	Ubuntu 14.04.5 LTS	clang version 5.0.0-svn312333-1~exp1 (branches/release_50)
Clang Xcode 6.4	Darwin Kernel Version 14.5.0 (OS X 10.10.3)	Apple LLVM version 6.1.0 (clang-602.0.53) (based on LLVM 3.6.0svn)
Clang Xcode 7.3	Darwin Kernel Version 15.6.0 (OS X 10.10.5)	Apple LLVM version 7.3.0 (clang-703.0.31)
Clang Xcode 8.3	Darwin Kernel Version 16.6.0 (OS X 10.12.5)	Apple LLVM version 8.1.0 (clang-802.0.42)
Visual Studio 14 2015	Visual Studio 2015 with Update 3	MSVC 19.0.24215.1
Visual Studio 15 2017	Visual Studio 2017	MSVC 19.11.25507.1
Visual Studio 14 2015 (Clang/LLVM)	Visual Studio 2015 with Update 3	Clang 4.0.0

NOTES

• GCC 4.9: constexpr support is not available for visit and relational operators.
• Enabling libc++ std::variant tests require -std=c++17 support.

CMake Variables

• MPARK_VARIANT_INCLUDE_TESTS:STRING (default: "")

  Semicolon-separated list of tests to build. Possible values are mpark, and libc++.

  NOTE: The libc++ std::variant tests are built with -std=c++17.

Unit Tests

Refer to test/README.md.

License

Distributed under the Boost Software License, Version 1.0.