range-v3

Range library for C++14/17/20. This code was the basis of a formal proposal to add range support to the C++ standard library. That proposal evolved through a Technical Specification, and finally into P0896R4 "The One Ranges Proposal" which was merged into the C++20 working drafts in November 2018.

About:

Ranges are an extension of the Standard Template Library that makes its iterators and algorithms more powerful by making them composable. Unlike other range-like solutions which seek to do away with iterators, in range-v3 ranges are an abstration layer on top of iterators.

Range-v3 is built on three pillars: Views, Actions, and Algorithms. The algorithms are the same as those with which you are already familiar in the STL, except that in range-v3 all the algorithms have overloads that take ranges in addition to the overloads that take iterators. Views are composable adaptations of ranges where the adaptation happens lazily as the view is iterated. And an action is an eager application of an algorithm to a container that mutates the container in-place and returns it for further processing.

Views and actions use the pipe syntax (e.g., rng | adapt1 | adapt2 | ...) so your code is terse and readable from left to right.

Documentation:

Check out the (woefully incomplete) documentation here.

Other resources (mind the dates, the library probably has changed since then):

• Usage:

  • Talk: CppCon 2015: Eric Niebler "Ranges for the Standard Library", 2015.
  • A slice of Python in C++, 07.12.2014.
  • Actions (back then called Container Algorithms), 23.11.2014.
  • Range comprehensions, 27.04.2014.
  • Input iterators vs input ranges, 07.11.2013.

• Design / Implementation:

  • Rationale behind range-v3: N4128: Ranges for the standard library Revision 1, 2014.
  • Ranges TS: N4560: C++ Extensions for Ranges, 2015.
  • Implementation of customization points in range-v3:
    • N4381: Suggested Design for Customization Points, 2015.
    • P0386: Inline variables, 2016.
    • Customization Point Design in C++11 and Beyond, 2014.
  • Proxy iterators in range-v3:
    • D0022: Proxy Iterators for the Ranges Extensions.
    • To Be or Not to Be (an Iterator), 2015.
    • Iterators++: Part1, 2015.
    • Iterators++: Part2, 2015.
    • Iterators++: Part3, 2015.
  • Metaprogramming utilities:
    • See the meta documentation, the library has changed significantly since the 2014 blog post.
  • Concept emulation layer: Concept checking in C++11, 2013.
  • C++Now 2014: Eric Niebler "C++11 Library Design", 2014.

License:

Most of the source code in this project are mine, and those are under the Boost Software License. Parts are taken from Alex Stepanov's Elements of Programming, Howard Hinnant's libc++, and from the SGI STL. Please see the attached LICENSE file and the CREDITS file for the licensing and acknowledgments.

Supported Compilers

The code is known to work on the following compilers:

• clang 3.9 (or later)
• GCC 6.5 (or later)
• Clang/LLVM 6 (or later) on Windows (older versions may work - we haven't tested.)
• Visual Studio 2019 (or later) on Windows, with some caveats due to range-v3's strict conformance requirements:
  • range-v3 needs /std:c++latest /permissive-
  • range-v3 needs a fully conforming preprocessor, so /experimental:preprocessor is necessary. Note that the conforming preprocessor diagnoses C5105 "macro expansion producing 'defined' has undefined behavior" in some of the Windows SDK headers, so you'll probably want to suppress that warning with /wd5105.

[ Note: We've "retired" support for Clang/C2 with the VS2015 toolset (i.e., the v140_clang_c2 toolset) which Microsoft no longer supports for C++ use. We no longer have CI runs, but haven't gone out of our way to break anything, so it will likely continue to work. ]

Development Status: This code is fairly stable, well-tested, and suitable for casual use, although currently lacking documentation. In general, no promise is made about support or long-term stability. This code will evolve without regard to backwards compatibility.

A notable exception is anything found within the ranges::cpp20 namespace. Those components will change rarely or (preferably) never at all.

Build status

• on Travis-CI:
• on AppVeyor:

Say Thanks!

I do this work because I love it and because I love C++ and want it to be as excellent as I know it can be. If you like my work and are looking for a way to say thank you, you can leave a supportive comment on my blog. Or you could leave me some kudos on my Open Hub range-v3 contribution page. Just click the Give Kudos button here.