https://github.com/avakar/metapp

A small header-only C++ library for manipulating lists of types.
https://github.com/avakar/metapp

Last synced: about 2 months ago
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A small header-only C++ library for manipulating lists of types.

• Host: GitHub
• URL: https://github.com/avakar/metapp
• Owner: avakar
• Created: 2017-05-22T16:47:31.000Z (about 8 years ago)
• Default Branch: master
• Last Pushed: 2017-05-22T18:10:17.000Z (about 8 years ago)
• Last Synced: 2025-04-12T19:57:45.577Z (about 2 months ago)
• Language: C++
• Homepage:
• Size: 5.86 KB
• Stars: 3
• Watchers: 3
• Forks: 1
• Open Issues: 0
• Metadata Files:
  • Readme: README.md

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README

        
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# Meta++

A small header-only C++ library for manipulating lists of types.

## Installation

Clone anywhere and make "include" directory visible. If you're using CMake, you can link against avakar_metapp target and the include directories will be made available automatically.

## Getting started

Lists of types are represented using `avakar::meta::list` template.

    #include 

    namespace meta = avakar::meta;

    

    using L = meta::list;

Lists can be empty or contain repeated elements. Note that the `list` class is incomplete and cannot be instantiated. There is a collection of metafunctions one would expect to have to manipulate lists. 

  * `length`: returns `n`.

  * `contains`: returns true if there is an `i` such that `T_i == T`.

  * `contains_unique`: returns true if there is exactly one `i` such that `T_i == T`.

  * `first_index_of`: returns the first `i` such that `T_i == T`. The class is incomplete if `!contains`.

  * `index_of`: returns `i` such that `T_i == T`. Incomplete if `!contains_unique`.

  * `sub`: returns `T_i`.

  * `concat`: returns a concatenation of lists `L_i`. Arguments that are not `list` are wrapped in one; as such this metafunction also works as an append.

## Choosing a type at runtime

The major reason for the library is the function `visit`, which accepts a list as a template argument, and an index and a visitor function as its regular arguments. Visit calls the visitor with an argument of type `list_item`.

    void * storage = /*...*/;

    using L = meta::list;

    size_t index = 1;

    // prints the content of `storage` as if it contained a std::string

    meta::visit(index, [storage](auto m) {

        std::cout << *static_cast(storage) << "\n";

    });