Deimos

From D Wiki
Jump to: navigation, search

Deimos is an endeavor to host and maintain D bindings for popular non-D libraries and projects, notably which have a C ABI.

The original proposal for Deimos can be found in DIP12.

Rationale

Having a central place for bindings allows them to be:

  1. easily discovered;
  2. maintained by the community, even past the original author's interest in the project.

Agreeing on a common layout and conventions will also make usage and contribution easier.

Hosting bindings under the D-Programming-Deimos organization is orthogonal to, and provides benefits in addition to, publishing the bindings on the Dub registry (code.dlang.org).

Description

A repository for each project is created under https://github.com/D-Programming-Deimos.

Following these conventions should maximize consistency and simplify distribution / usage:

Directory structure

Repositories have the following directory structure:

|--- library name (repository root)
    |--- README.md
    |--- dub.sdl
    |--- C
        |--- foo.h
        |--- bar
            |--- baz.h
    |--- deimos
        |--- foo.d
        |--- bar
            |--- baz.d

The C directory should contain a copy of the original C headers that were translated. Doing so allows updating them to newer versions easily, as only the diffs between the old and new C headers need to be translated and applied to the D bindings.

The layout of the C directory corresponds to /usr/include on UNIX machines. Thus, if a C header file would be installed to /usr/include/bar/baz.h, in the repository it should be added as C/bar/baz.h.

The D module/package names should map such that #include <path/to/header.h> should correspond to import path.to.header;.

Module and package names should match file and directory names, i.e. the module path.to.header should be at deimos/path/to/header.d (or .di), but not somewhere else.

Recommendations

  • Each library should contain a README file (README, or README.md for Markdown syntax) in the root folder.
    The README file should contain exact source and version of the C library.
    Any specific notes regarding the usage or translation of the bindings should also be placed there.
  • Every library should contain a simple D example under an examples directory.

Translation

  • Deimos repositories should aim to provide 1:1 bindings of C APIs, without any higher-level wrapping. Higher-level wrappers can be included alongside low-level ones, but are best provided as separate projects / repositories on top of the Deimos bindings.
    Rationale:
    • Low-level bindings will generally satisfy the constraints of all D projects, regardless of platform / architecture / toolchain, and usable from nothrow / @nogc / -betterC code. Higher-level bindings will generally compromise on some of these constraints in order to provide a more idiomatic D API.
    • Low-level bindings, being a 1:1 translation of C header files, are generally uncontroversial (as in, there isn't really more than one way to write them). Higher-level wrappers can be potentially written using a variety of approaches / paradigms / style, thus there not being one single obviously correct way to write them.
  • The D import files should try to do as least modifications as possible to simplify updates of the C headers. This includes leaving comments intact (unless e.g. adapting them to DDoc syntax).
  • The copyright for the D import files should match the one being used by the C header as they constitute a derived work.
  • If the C header file has a name that is a D keyword, an underscore will be appended to the D module name and file name.
  • If a C type name matches a C function name (e.g. stat), the type name will have a _t appended (e.g. stat_t).
  • Ideally, translated header modules should not require linkage of any D binary. Macros and inline functions can be translated as templates, e.g.:
    • C: #define GET(x) x.value
    • D: int GET(X)(X x) { return x.value; }

    One way to test if your bindings satisfy this property is to write a program making use of these bindings, and compile it without including the bindings' source files in the compilation, e.g. dmd -Lmytestlib.lib test.d (as opposed to using dub, rdmd, or dmd -i).

Versioning

Version tags should match the ones being used by the C headers.

For repositories providing bindings for projects which use a versioning scheme incompatible with semantic versioning, the preferred approach is to use semantic versioning and append the original library version past a + sign (example: OpenSSL).

Submitting

To propose a new binding project to be added to Deimos, contact a member of the D-Programming-Deimos organization:

https://github.com/orgs/D-Programming-Deimos/people

If you are already a member of D-Programming-Deimos, consider making your membership public, so that you can be contacted by submitters.

Contributing

To submit updates or improvements, send a pull request as usual.

If you get no response to your pull request, or if you would like to be added as a project maintainer, ping an organization member.