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https://github.com/arximboldi/lager

C++ library for value-oriented design using the unidirectional data-flow architecture — Redux for C++
https://github.com/arximboldi/lager

cpp17 functional-programming interactive library redux value-semantics

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C++ library for value-oriented design using the unidirectional data-flow architecture — Redux for C++

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  Logotype



.. include:introduction/start



**lager** is a C++ library to assist `value-oriented design`_ by

implementing the `unidirectional data-flow architecture`_.  It is

heavily inspired by Elm_ and Redux_, and enables composable designs by

promoting the use of simple value types and testable application logic

via pure functions.  And you get time-travel for free!



.. _unidirectional data-flow architecture: https://www.exclamationlabs.com/blog/the-case-for-unidirectional-data-flow

.. _Elm: https://guide.elm-lang.org/architecture

.. _Redux: https://redux.js.org/introduction/getting-started

.. _value-oriented design: https://www.youtube.com/watch?v=_oBx_NbLghY



* **Documentation** (Contents_)

* **Code** (GitHub_)

* **CppRussia-Piter 2019 Talk**: *Squaring the circle* (`YouTube

  `_, `Slides

  `_)

* **CppCon 2018 Talk**: *The most valuable values* (`YouTube

  `_, `Slides

  `_)

* **C++ on Sea 2019 Talk**: *Postmodern immutable data-structures*

  (`YouTube `_, `Slides

  `_)



.. _contents: https://sinusoid.es/lager/#contents

.. _github: https://github.com/arximboldi/lager



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  This project is part of a long-term vision helping interactive and

  concurrent C++ programs become easier to write. **Help this project's

  long term sustainability by becoming a patron or buying a

  sponsorship package:** [email protected]



.. include:index/end



Examples

--------



For a guided introductory tour with **code samples**, please read the

`architecture overview`_ section. Other examples:



.. _architecture overview: https://sinusoid.es/lager/architecture.html



* **Counter**, a minimalistic example with multiple UIs (`link

  `_).

* **Autopong**, a basic game using SDL2 (`link

  `_).

* **Ewig**, a terminal text editor with undo, asynchronous loading,

  and more (`link `_).



Why?

----



Most interactive software of the last few decades has been written

using an object-oriented interpretation of the `Model View

Controller`_ design.  This architecture provides nice separation of

concerns, allowing the core application logic to be separate from the

UI, and a good sense of modularity.  However, its reliance on stateful

object graphs makes the software hard to test or parallelize.  It's

reliance on fine-grained callbacks makes composition hard, resulting

in subtle problems that are hard to debug.



*Value-based unidirectional data-flow* tackles a few of these

problems:



* Thanks to immutability_ and value-types, it is very easy to add

  **concurrency** as threads can operate on their local copies of the

  data without mutexes or other flaky synchronization mechanisms.

  Instead, worker threads communicate their results back by *dispatching*

  actions to the main thread.



* The application logic is made of `pure functions`_ that can be easily

  **tested** and are fully reproducible.  They interact with the world

  via special side-effects procedures loosely coupled to the services

  they need via  `dependency injection`_.



* This also means that data and call-graphs are always trees or

  `DAGs`_ (instead of cyclical graphs), with *explicit composition*

  that is to trace and **debug**.  You can also always

  *snapshot* the state, making undo and time-travel easy peasy!



.. _immutability: https://github.com/arximboldi/immer

.. _pure functions: https://en.wikipedia.org/wiki/Pure_function

.. _model view controller:

   https://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93controller

.. _dependency injection:

   https://en.wikipedia.org/wiki/Dependency_injection

.. _DAGs: https://en.wikipedia.org/wiki/Directed_acyclic_graph



Dependencies

------------



This library is written in **C++17** and a compliant compiler and

standard library necessary.  It is `continuously tested`_ with GCC 7,

but it might work with other compilers and versions.



It also depends on `Zug`_ and `Boost Hana`_. Some optional extensions and modules

may have other dependencies documented in their respective sections.



.. _Zug: https://github.com/arximboldi/zug/

.. _Boost Hana: https://boostorg.github.io/hana

.. _continuously tested: https://travis-ci.org/arximboldi/immer



Usage

-----



This is a **header only** you can just copy the ``lager`` subfolder

somewhere in your *include path*.



Some components, like the time-travelling debugger, also require the

installation of extra files.



You can use `CMake`_ to install the library in your system once you

have manually cloned the repository::



    mkdir -p build && cd build

    cmake .. && sudo make install



.. _nix package manager: https://nixos.org/nix

.. _cmake: https://cmake.org/



Development

-----------



In order to develop the library, you will need to compile and run the

examples, tests and benchmarks.  These require some additional tools.

The easiest way to install them is by using the `Nix package

manager`_.  At the root of the repository just type::



    nix-shell



This will download all required dependencies and create an isolated

environment in which you can use these dependencies, without polluting

your system.



Then you can proceed to generate a development project using `CMake`_::



    mkdir build && cd build

    cmake ..



From then on, one may build and run all tests by doing::



    make check



License

-------



.. image:: https://raw.githubusercontent.com/arximboldi/lager/docs/doc/_static/mit.png

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   :target: https://opensource.org/licenses/MIT

   :align: right

   :width: 140 px



**This software is licensed under the MIT license**.



The full text of the license is can be accessed `via this link

`_ and is also included in the

``LICENSE`` file of this software package.