edwiincao / variant

C++11 Variant

Mapbox Variant

An alternative to boost::variant for C++11.

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

Depends

• Compiler supporting -std=c++11

Tested with

• g++-4.7
• g++-4.8
• clang++-3.4
• clang++-3.5
• Visual C++ Compiler November 2013 CTP
• Visual C++ Compiler 2014 CTP 4

Note: get the "2013 Nov CTP" release at http://www.microsoft.com/en-us/download/details.aspx?id=41151 and the 2014 CTP at http://www.visualstudio.com/en-us/downloads/visual-studio-14-ctp-vs.aspx

Usage

There is nothing to build, just include variant.hpp and recursive_wrapper.hpp in your project.

Tests

The tests depend on:

• Boost headers (for benchmarking against boost::variant)
• Boost built with --with-timer (used for benchmark timing)

On Unix systems set your boost includes and libs locations and run make test:

export LDFLAGS='-L/opt/boost/lib'
export CXXFLAGS='-I/opt/boost/include'
make test

On windows do:

vcbuild

Benchmark

On Unix systems run the benchmark like:

make bench

Check object sizes

make sizes /path/to/boost/variant.hpp