short-description: Definition of build targets ...
Meson provides four kinds of build targets: executables, libraries (which can be set to be built as static or shared or both of them at the build configuration time), static libraries, and shared libraries. They are created with the commands executable, library, static_library and shared_library, respectively. All objects created in this way are immutable. That is, you cannot change any aspect of them after they have been constructed. This ensures that all information pertaining to a given build target is specified in one well defined place.
Libraries and executables
As an example, here is how you would build a library.
project('shared lib', 'c') library('mylib', 'source.c')
It is generally preferred to use the library command instead of shared_library and static_library and then configure which libraries (static or shared or both of them) will be built at the build configuration time using the default_library built-in option.
In Unix-like operating systems, shared libraries can be versioned. Meson supports this with keyword arguments, which will be ignored if the library is configured as static at the compile time.
project('shared lib', 'c') library('mylib', 'source.c', version : '1.2.3', soversion : '1')
It is common to build a library and then an executable that links against it. This is supported as well.
project('shared lib', 'c') lib = library('mylib', 'source.c') executable('program', 'prog.c', link_with : lib)
Meson sets things up so that the resulting executable can be run directly from the build directory. There is no need to write shell scripts or set environment variables.
One target can have multiple language source files.
project('multilang', 'c', 'cpp') executable('multiexe', 'file.c', 'file2.cc')
Object files
Sometimes you can't build files from sources but need to utilize an existing object file. A typical case is using an object file provided by a third party. Object files can be specified just like sources.
exe = executable('myexe', 'source.cpp', objects : 'third_party_object.o')
A different case is when you want to use object files built in one target directly in another. A typical case is when you build a shared library and it has an internal class that is not exported in the ABI. This means you can‘t access it even if you link against the library. Typical workarounds for this include building both a shared and static version of the library or putting the source file in the test executable’s source list. Both of these approaches cause the source to be built twice, which is slow.
In Meson you can extract object files from targets and use them as-is on other targets. This is the syntax for it.
lib = shared_library('somelib', 'internalclass.cc', 'file.cc', ...) eo = lib.extract_objects('internalclass.cc') executable('classtest', 'classtest.cpp', objects : eo)
Here we take the internal class object and use it directly in the test. The source file is only compiled once.
Note that careless use of this feature may cause strange bugs. As an example trying to use objects of an executable or static library in a shared library will not work because shared library objects require special compiler flags. Getting this right is the user's responsibility. For this reason it is strongly recommended that you only use this feature for generating unit test executables in the manner described above.