Helpers for Ranges + Coroutines

UPDATE

The code in this repository is now obsolete. The range-v3 library now contains a generator that works as a View. Please use that instead as it is more feature-complete and correct that the implementation in this repository.

Introduction

This repository contains some helpers for and demonstrations of using Ranges and Coroutines together.

Currently this code has only been tested using Visual Studio 2017 and a build of specific branches of clang and libc++.

generator - a Range-friendly generator

Included in Microsoft's Coroutines support library is the class template std::experimental::generator. This allows a coroutine to return a lazy sequence of values using co_yield.

This allows code like:

generator<int> infinite_sequence() {
  for (int i = 0; ; ++i) {
    co_yield i;
  }
}

for (int i : infinite_sequence()) {
  cout << i;
  if (i > 10) break;
}

This is wonderful, however these generator objects can't be using alongside the also wonderful range-v3 library. This is due to generator not satisfying all of the requirements of the Range concept (see https://github.com/Microsoft/Range-V3-VS2015/issues/12).

The generator class template included in this repository is intended to be a drop-in replacement for Microsoft's one. It has the advantage that it supports Ranges. It has the disadvantage that it is ever-so-slightly less efficient because it has to maintain a reference count in order to support copying.

It allows you to write code like:

generator<int> infinite_sequence() {
  for (int i = 0; ; ++i) {
    co_yield i;
  }
}

infinite_sequence()
  | take(10)
  | for_each([](int x) { cout << x; });

Also, it's easy to write an adaptor using a coroutine:

template <typename InputRange, typename UnaryPredicate>
auto filter_co(InputRange range, UnaryPredicate pred)
    -> generator<ranges::range_value_t<InputRange>> {
  for (auto&& x : range) {
    if (pred(x)) {
      co_yield x;
    }
  }
}

template <typename UnaryPredicate>
auto filter_co(UnaryPredicate pred) {
  return ranges::make_pipeable([pred = std::move(pred)](auto&& rng) {
    return filter_co(std::forward<decltype(rng)>(rng), std::move(pred));
  });
}

infinite_sequence()
  | filter_co([](int x) { return x % 2 == 0; })
  | take(10)
  | for_each([](int x) { cout << x; });

Dependencies

To build the tests, you will need either:

• Visual Studio 2017 (2015 might also work - not tested)
• Clang and libc++ built from particular branches (see below)

The following are included:

• range-v3
• spdlog (currently not)
• doctest

The library itself is header-only and only depends on having an <experimental/coroutine> header available.

Building

Visual Studio

Clang

Currently, you will need to build your own clang and libc++. Hopefully this stuff will get merged into those projects' trunks soon.

Checkout llvm, clang, libcxx and libcxxabi

cd $SRC_ROOT # you choose this directory
git clone -b merge0307 https://github.com/GorNishanov/llvm.git
cd llvm/tools
git clone -b merge0307 https://github.com/GorNishanov/clang.git
cd ../projects
git clone -b coroutines https://github.com/efcs/libcxx.git
git clone https://github.com/llvm-mirror/libcxxabi.git

Configure

cd $SRC_ROOT
mkdir build
cd build
cmake ..

Build

cd $SRC_ROOT/build
make # use -jN if you have lots of RAM

Configure generator

cd $LOCATION_OF_THIS_FILE
mkdir build
cd build
cmake CXX=$SRC_ROOT/build/bin/clang++ ..

Build generator

make

Run tests

LD_LIBRARY_PATH=$SRC_ROOT/build/lib ./generator/generator_test