---
title: D
short-description: Compiling D sources
...

# Compiling D applications

Meson has support for compiling D programs. A minimal `meson.build` file for D looks like this:

```meson
project('myapp', 'd')

executable('myapp', 'app.d')
```

## Compiling different versions

If you are using the [version()](https://dlang.org/spec/version.html) feature for conditional compilation, you can use it using the `d_module_versions`
target property:
```meson
project('myapp', 'd')
executable('myapp', 'app.d', d_module_versions: ['Demo', 'FeatureA'])
```

## Using embedded unittests

If you are using embedded [unittest functions](https://dlang.org/spec/unittest.html), your source code needs to be compiled twice, once in regular
mode, and once with unittests active. This is done by setting the `d_unittest` target property to `true`.
Meson will only ever pass the respective compiler's `-unittest` flag, and never have the compiler generate an empty main function.
If you need that feature in a portable way, create an empty `main()` function for unittests yourself, since the GNU D compiler
does not have this feature.

This is an example for using D unittests with Meson:
```meson
project('myapp_tested', 'd')

myapp_src = ['app.d', 'alpha.d', 'beta.d']
executable('myapp', myapp_src)

test_exe = executable('myapp_test', myapp_src, d_unittest: true)
test('myapptest', test_exe)
```

# Compiling D libraries and installing them

Building D libraries is a straightforward process, not different from how C libraries are built in Meson. You should generate a pkg-config file
and install it, in order to make other software on the system find the dependency once it is installed.

This is an example on how to build a D shared library:
```meson
project('mylib', 'd', version: '1.2.0')

project_soversion = 0
glib_dep = dependency('glib-2.0')

my_lib = library('mylib',
    ['src/mylib/libfunctions.d'],
    dependencies: [glib_dep],
    install: true,
    version: meson.project_version(),
    soversion: project_soversion,
    d_module_versions: ['FeatureA', 'featureB']
)
pkgc.generate(name: 'mylib',
              libraries: my_lib,
              subdirs: 'd/mylib',
              version: meson.project_version(),
              description: 'A simple example D library.',
              d_module_versions: ['FeatureA']
)
install_subdir('src/mylib/', install_dir: 'include/d/mylib/')
```

It is important to make the D sources install in a subdirectory in the include path, in this case `/usr/include/d/mylib/mylib`.
All D compilers include the `/usr/include/d` directory by default, and if your library would be installed into `/usr/include/d/mylib`, there
is a high chance that, when you compile your project again on a machine where you installed it, the compiler will prefer the old installed include over
the new version in the source tree, leading to very confusing errors.

This is an example of how to use the D library we just built and installed in an application:
```meson
project('myapp', 'd')

mylib_dep = dependency('mylib', version: '>= 1.2.0')
myapp_src = ['app.d', 'alpha.d', 'beta.d']
executable('myapp', myapp_src, dependencies: [mylib_dep])
```

Please keep in mind that the library and executable would both need to be built with the exact same D compiler and D compiler version. The D ABI is not
stable across compilers and their versions, and mixing compilers will lead to problems.
