Platform Specific Projects

When a project involves platform-specific code, some consideration needs to be made to the LID file and registry, as well as the layout of code. As an example, consider the io and system libraries.

In summary, there must be a LID file for each version of your library that needs some platform-specific code, and a platform-specific registry file that points to the appropriate LID file.

LID File

For further details of the LID file format, see LID File Format.

  1. The Library keyword

    The library keyword remains the same across all platforms since it is, after all, a platform-dependent version of that library:

    Keyword

    unix-io.lid

    win32-io.lid

    Library:

    io

    io

  2. The Files keyword

    Each platform’s project may contain files that are the same in each platform, as well as files which are present in one but not in another:

    Keyword

    unix-io.lid

    win32-io.lid

    Files:

    buffered-format

    buffered-format

    format-condition

    format-condition

    unix-interface

    win32-interface

    unix-file-accessor

    win32-file-accessor

    unix-standard-io

    win32-standard-io

    format-out

    format-out

    (etc)

    (etc)

    C-Source-Files:

    unix-portability.c

    RC-Files:

    version.rc

  3. The C-Libraries keyword

    Each platform’s project will probably require a different set of linked libraries. (Here we use an example from the “system” library as the “io” library doesn’t link directly against any C libraries.)

    Keyword

    x86_64-linux-system.lid

    x86-win32-system.lid

    C-Libraries:

    -ldl

    advapi32.lib

    shell32.lib

  4. The Platforms keyword

    Platform-specific LID files should use the Platforms keyword to indicate which platforms they apply to. This helps the deft update command decide which registry files to create. If there is no Platforms keyword deft assumes the LID file applies to the current platform and creates a registry file for its library.

    Keyword

    unix-io.lid

    win32-io.lid

    Platforms:

    x86_64-linux

    win32

    x86_64-darwin

    x86_64-freebsd

LID File Inheritance

When LID files are almost identical, it can be useful to create a base LID file and inherit it, overriding whatever is necessary for each platform. A per-platform LID file might look like:

Library:        uv
LID:            uv-posix.lid
C-libraries:    -framework CoreServices

Registry

For further details of setting up the registry entries, see Using Source Registries.

Normally, when a reference to a platform-independent project is placed in the registry, it is put into the “generic” directory. Platform dependent projects are placed in subdirectories named for the platform. For example, opendylan/sources/registry/x86_64-linux/io points to unix-io.lid and opendylan/sources/registry/x86-win32/io points to win32-io.lid.

Code Layout

The “io” library is laid out in the following manner:

  1. All platform-specific code is inside a single module (io-internals).

  2. *-interface.dylan contains the low-level functions accessing the platform-specific libraries (e.g. unix-read, win32-read).

  3. *-file-accessor.dylan uses the functions from (2) to produce a platform-independent API (e.g. accessor-read-into!).

  4. Only those methods from (3) are exported from the module.

Note

Most libraries that are portable aren’t as complex in their layout as the io library and don’t require separate modules.