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)

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)

find_package(mpark_variant 1.3.0 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:

NOTES

• GCC 4.8/4.9: 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.