beman.copyable_function: A Beman Library Implementation of copyable_function (P2548)

beman.copyable_function is a type-erased function wrapper that can represent any copyable callable matching the function signature R(Args...). The library conforms to the The Beman Standard.

Implements: std::copyable_function proposed in P2548R6.

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

License

beman.copyable_function is licensed under the Apache License v2.0 with LLVM Exceptions.

Usage

The following code snippet illustrates copyable_function:

#include <beman/copyable_function/copyable_function.hpp>

// a Callable object
struct Callable {
    int operator()() { return 42; }
    int operator()() const noexcept { return 43; }
};

int main()
{
    beman::copyable_function<int()> f(Callable{});
    int x = f();
    return 0;
}

Full runnable examples can be found in examples/.

Dependencies

Build Environment

This project requires at least the following to build:

• A C++ compiler that conforms to the C++17 standard or greater
• CMake 3.30 or later
• (Test Only) GoogleTest

You can disable building tests by setting CMake option BEMAN_COPYABLE_FUNCTION_BUILD_TESTS to OFF when configuring the project.

Supported Platforms

Compiler	Version	C++ Standards	Standard Library
GCC	15-13	C++26, C++23	libstdc++
GCC	12	C++23	libstdc++
Clang	22-19	C++26, C++23	libstdc++, libc++
Clang	18	C++26, C++23	libc++
Clang	18	C++23	libstdc++
Clang	17	C++26, C++23	libc++
AppleClang	latest	C++26, C++23	libc++
MSVC	latest	C++23	MSVC STL

Development

See the Contributing Guidelines.

Integrate beman.copyable_function into your project

Build

You can build copyable_function using a CMake workflow preset:

cmake --workflow --preset gcc-release

To list available workflow presets, you can invoke:

cmake --list-presets=workflow

For details on building beman.copyable_function without using a CMake preset, refer to the Contributing Guidelines.

Installation

To install beman.copyable_function globally after building with the gcc-release preset, you can run:

sudo cmake --install build/gcc-release

Alternatively, to install to a prefix, for example /opt/beman, you can run:

sudo cmake --install build/gcc-release --prefix /opt/beman

This will generate the following directory structure:

/opt/beman
├── include
│   └── beman
│       └── copyable_function
│           ├── copyable_function.hpp
│           └── ...
└── lib
    └── cmake
        └── beman.copyable_function
            ├── beman.copyable_function-config-version.cmake
            ├── beman.copyable_function-config.cmake
            └── beman.copyable_function-targets.cmake

CMake Configuration

If you installed beman.copyable_function to a prefix, you can specify that prefix to your CMake project using CMAKE_PREFIX_PATH; for example, -DCMAKE_PREFIX_PATH=/opt/beman.

You need to bring in the beman.copyable_function package to define the beman::copyable_function CMake target:

find_package(beman.copyable_function REQUIRED)

You will then need to add beman::copyable_function to the link libraries of any libraries or executables that include beman.copyable_function headers.

target_link_libraries(yourlib PUBLIC beman::copyable_function)

Using beman.copyable_function

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

#include <beman/copyable_function/copyable_function.hpp>

Note

beman.copyable_function headers are to be included with the beman/copyable_function/ prefix. Altering include search paths to spell the include target another way (e.g. #include <copyable_function.hpp>) is unsupported.

Contributing

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