beman.scan_view: A range adaptor that is a lazy view version of std::inclusive_scan

Implements: std::views::scan proposed in views::scan (P3351R4).

Difference from the paper:

• Implemented reserve_hint are hidden behind a feature-test macro.

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

License

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

Usage

views::scan is a range adaptor that takes a range and a function that takes the current element and the current state as parameters. Basically, views::scan is a lazy view version of std::inclusive_scan, or views::transform with a stateful function.

#include <functional>
#include <print>
#include <vector>

#include <beman/scan_view/scan.hpp>

namespace exe = beman::scan_view;

// Example given in the paper for `views::scan`. (Needs C++23)
int main()
{
    std::vector vec{1, 2, 3, 4, 5, 4, 3, 2, 1};

    // [1, 3, 6, 10, 15, 19, 22, 24, 25]
    std::println("{}", vec | exe::scan(std::plus{}));
    // [11, 13, 16, 20, 25, 29, 32, 34, 35]
    std::println("{}", vec | exe::scan(std::plus{}, 10));
    // [1, 2, 3, 4, 5, 5, 5, 5, 5]
    std::println("{}", vec | exe::scan(std::ranges::max));
    // [3, 3, 3, 4, 5, 5, 5, 5, 5]
    std::println("{}", vec | exe::scan(std::ranges::max, 3));

    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++20 standard or greater
• CMake 3.30 or later
• (Test Only) GoogleTest

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

Supported Platforms

Compiler	Version	C++ Standards	Standard Library
GCC	16-13	C++26-C++20	libstdc++
GCC	12-11	C++23, C++20	libstdc++
Clang	20-19	C++26-C++20	libstdc++, libc++
Clang	18-17	C++26-C++20	libc++
Clang	18-17	C++20	libstdc++
AppleClang	latest	C++26-C++20	libc++
MSVC	latest	C++23	MSVC STL

Development

See the Contributing Guidelines.

Integrate beman.scan_view into your project

Build

You can build scan_view 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.scan_view without using a CMake preset, refer to the Contributing Guidelines.

Installation

Vcpkg

The preferred way to install scan_view is via vcpkg. To do so, after installing vcpkg itself, you need to add support for the Beman project's vcpkg registry by configuring a vcpkg-configuration.json file (which scan_view provides).

Then, simply run vcpkg install beman-scan-view.

Manual

To install beman.scan_view 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
│       └── scan_view
│           ├── scan.hpp
│           └── ...
└── lib
    └── cmake
        └── beman.scan_view
            ├── beman.scan_view-config-version.cmake
            ├── beman.scan_view-config.cmake
            └── beman.scan_view-targets.cmake

CMake Configuration

If you installed beman.scan_view 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.scan_view package to define the beman::scan_view CMake target:

find_package(beman.scan_view REQUIRED)

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

target_link_libraries(yourlib PUBLIC beman::scan_view)

Using beman.scan_view

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

#include <beman/scan_view/scan.hpp>

Note

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