beman.exemplar: A Beman Library Exemplar

beman.exemplar is a minimal C++ library conforming to The Beman Standard. This can be used as a template for those intending to write Beman libraries. It may also find use as a minimal and modern C++ project structure.

Implements: std::identity proposed in Standard Library Concepts (P0898R3).

Status: Under development and not yet ready for production use.

Usage

std::identity is a function object type whose operator() returns its argument unchanged. std::identity serves as the default projection in constrained algorithms. Its direct usage is usually not needed.

Usage: default projection in constrained algorithms

The following code snippet illustrates how we can achieve a default projection using beman::exemplar::identity:

#include <beman/exemplar/identity.hpp>

namespace exe = beman::exemplar;

// Class with a pair of values.
struct Pair
{
    int n;
    std::string s;

    // Output the pair in the form {n, s}.
    // Used by the range-printer if no custom projection is provided (default: identity projection).
    friend std::ostream &operator<<(std::ostream &os, const Pair &p)
    {
        return os << "Pair" << '{' << p.n << ", " << p.s << '}';
    }
};

// A range-printer that can print projected (modified) elements of a range.
// All the elements of the range are printed in the form {element1, element2, ...}.
// e.g., pairs with identity: Pair{1, one}, Pair{2, two}, Pair{3, three}
// e.g., pairs with custom projection: {1:one, 2:two, 3:three}
template <std::ranges::input_range R,
          typename Projection>
void print(const std::string_view rem, R &&range, Projection projection = exe::identity>)
{
    std::cout << rem << '{';
    std::ranges::for_each(
        range,
        [O = 0](const auto &o) mutable
        { std::cout << (O++ ? ", " : "") << o; },
        projection);
    std::cout << "}\n";
};

int main()
{
    // A vector of pairs to print.
    const std::vector<Pair> pairs = {
        {1, "one"},
        {2, "two"},
        {3, "three"},
    };

    // Print the pairs using the default projection.
    print("\tpairs with beman: ", pairs);

    return 0;
}

Full runnable examples can be found in examples/.

Dependencies

Build Environment

This project requires at least the following to build:

• C++17
• CMake 3.25
• (Test Only) GoogleTest

You can disable building tests by setting cmake option BEMAN_EXEMPLAR_BUILD_TESTS to OFF when configuring the project.

Even when tests are being built and run, some will not be compiled unless provided compiler support C++20 or ranges capabilities enabled.

Tip

In the logs you will be able to see if there are any examples that aren't enabled due to compiler capabilities or the configured C++ version.

Below is an example:

-- Looking for __cpp_lib_ranges
-- Looking for __cpp_lib_ranges - not found
CMake Warning at examples/CMakeLists.txt:12 (message):
  Missing range support! Skip: identity_as_default_projection


Examples to be built: identity_direct_usage

Supported Platforms

This project officially supports:

• GNU GCC Compiler [version 12-14]
• LLVM Clang++ Compiler [version 17-20]
• AppleClang compiler on Mac OS
• MSVC compiler on Windows

Note

Versions outside of this range would likely work as well, especially if you're using a version above the given range (e.g. HEAD/ nightly). These development environments are verified using our CI configuration.

Development

Develop using GitHub Codespace

This project supports GitHub Codespace via Development Containers, which allows rapid development and instant hacking in your browser. We recommend you using GitHub codespace to explore this project as this requires minimal setup.

You can create a codespace for this project by clicking this badge:

For more detailed documentation regarding creating and developing inside of GitHub codespaces, please reference this doc.

Note

The codespace container may take up to 5 minutes to build and spin-up, this is normal as we need to build a custom docker container to setup an environment appropriate for beman projects.

Develop locally on your machines

For Linux based systems

Beman libraries requires recent versions of CMake, we advice you download CMake directly from CMake's website or install via the Kitware apt library.

A supported compiler should be available from your package manager. Alternatively you could use an install script from official compiler vendors.

Here is an example of how to install the latest stable version of clang as per the official LLVM install guide.

bash -c "$(wget -O - https://apt.llvm.org/llvm.sh)"

If the included test suite is being built and run, a GoogleTest library will be required. Here is an example of installing GoogleTest on a Debian-based Linux environment:

apt install libgtest-dev

The precise command and package name will vary depending on the Linux OS you are using. Be sure to consult documentation and the package repository for the system you are using.

For MacOS based systems

Beman libraries require recent versions of CMake. You can use Homebrew to install the latest major version of CMake.

brew install cmake

A supported compiler is also available from brew.

For example, you can install latest major release of Clang++ compiler as:

brew install llvm

Configure and Build the Project Using CMake Presets

This project recommends using CMake Presets to configure, build and test the project. Appropriate presets for major compilers have been included by default. You can use cmake --list-presets to see all available presets.

Here is an example to invoke the gcc-debug preset.

cmake --workflow --preset gcc-debug

Generally, there's two kinds of presets, debug and release.

The debug presets are designed to aid development, so it has debugging instrumentation enabled and as many sanitizers turned on as possible.

Note

The set of sanitizer supports are different across compilers. You can checkout the exact set compiler arguments by looking at the toolchain files under the cmake directory.

The release presets are designed for use in production environments, thus it has the highest optimization turned on (e.g. O3).

Configure and Build Manually

While CMake Presets are convenient, you might want to set different configuration or compiler arguments than any provided preset supports.

To configure, build and test the project with extra arguments, you can run this sets of command.

cmake -B build -S . -DCMAKE_CXX_STANDARD=20 # Your extra arguments here.
cmake --build build
ctest --test-dir build

Important

Beman projects are passive projects, therefore, you will need to specify C++ version via CMAKE_CXX_STANDARD when manually configuring the project.

Project specific configure arguments

When configuring the project manually, you can pass an array of project specific CMake configs to customize your build.

Project specific options are prefixed with BEMAN_EXEMPLAR. You can see the list of available options with:

cmake -LH | grep "BEMAN_EXEMPLAR" -C 2

Details of CMake arguments.

BEMAN_EXEMPLAR_BUILD_TESTS

Enable building tests and test infrastructure. Default: ON. Values: { ON, OFF }.

You can configure the project to have this option turned off via:

cmake -B build -S . -DCMAKE_CXX_STANDARD=20 -DBEMAN_EXEMPLAR_BUILD_TESTS=OFF

[!TIP] Because this project requires Google Tests as part of its development dependency, disable building tests avoids the project from pulling Google Tests from GitHub.

BEMAN_EXEMPLAR_BUILD_EXAMPLES

Enable building examples. Default: ON. Values: { ON, OFF }.

Build GoogleTest dependency from github.com

If you do not have GoogleTest installed on your development system, you may optionally configure this project to download a known-compatible release of GoogleTest from source and build it as well.

cmake -B build -S . -DCMAKE_PROJECT_TOP_LEVEL_INCLUDES=./cmake/use-fetch-content.cmake

The precise version of GoogleTest that will be used is maintained in ./lockfile.json.

Integrate beman.exemplar into your project

To use beman.exemplar in your C++ project, include an appropriate beman.exemplar header from your source code.

#include <beman/exemplar/identity.hpp>

Note

beman.exemplar headers are to be included with the beman/exemplar/ directories prefixed. It is not supported to alter include search paths to spell the include target another way. For instance, #include <identity.hpp> is not a supported interface.

How you will link your project against beman.exemplar will depend on your build system. CMake instructions are provided in following sections.

Linking your project to beman.exemplar with CMake

For CMake based projects, you will need to use the beman.exemplar CMake module to define the beman::exemplar CMake target:

find_package(beman.exemplar REQUIRED)

You will also need to add beman::exemplar to the link libraries of any libraries or executables that include beman.exemplar's header file.

target_link_libraries(yourlib PUBLIC beman::exemplar)

Produce beman.exemplar static library locally

You can include exemplar's headers locally by producing a static libbeman.exemplar.a library.

cmake --workflow --preset gcc-release
cmake --install build/gcc-release --prefix /opt/beman.exemplar

This will generate such directory structure at /opt/beman.exemplar.

/opt/beman.exemplar
├── include
│   └── beman
│       └── exemplar
│           └── identity.hpp
└── lib
    └── libbeman.exemplar.a

Contributing

Please do! You encourage you to checkout our contributor's guide. Issues and pull requests are appreciated.