A stand-alone library is a library that contains the necessary code to elaborate the Ada units that are included in the library. A stand-alone library is a convenient way to add an Ada subsystem to a more global system whose main is not in Ada since it makes the elaboration of the Ada part mostly transparent. However, stand-alone libraries are also useful when the main is in Ada: they provide a means for minimizing relinking & redeployment of complex systems when localized changes are made.
The name of a stand-alone library, specified with attribute
Library_Name, must have the syntax of an Ada identifier.
The most prominent characteristic of a stand-alone library is that it offers a
distinction between interface units and implementation units. Only the former
are visible to units outside the library. A stand-alone library project is thus
characterised by a third attribute, usually Library_Interface, in addition
to the two attributes that make a project a Library Project
Library_Dir). This third attribute may also be
Interfaces. Library_Interface only works when the interface is in Ada
and takes a list of units as parameter. Interfaces works for any supported
language and takes a list of sources as parameter.
Library_Interface. Other sources are considered implementation units.
for Library_Dir use "lib"; for Library_Name use "loggin"; for Library_Interface use ("lib1", "lib2"); -- unit names
Library_Interface, in which case, units have to be replaced by source files. For multi-language library projects, it is the only way to make the project a Stand-Alone Library project whose interface is not purely Ada.
standardis used the code to elaborate and finalize the library is embedded, when
encapsulatedis used the library can furthermore only depends on static libraries (including the GNAT runtime). This attribute can be set to
noto make it clear that the library should not be standalone in which case the
Library_Interfaceshould not defined.
for Library_Dir use "lib"; for Library_Name use "loggin"; for Library_Interface use ("lib1", "lib2"); -- unit names for Library_Standalone use "encapsulated";
In order to include the elaboration code in the stand-alone library, the binder
is invoked on the closure of the library units creating a package whose name
depends on the library name (^b~logging.ads/b^B$LOGGING.ADS/B^ in the example).
This binder-generated package includes initialization and finalization
procedures whose names depend on the library name (
loggingfinal in the example). The object corresponding to this package is
included in the library.
When a non-automatically initialized stand-alone library is used in an
executable, its initialization procedure must be called before any service of
the library is used. When the main subprogram is in Ada, it may mean that the
initialization procedure has to be called during elaboration of another
Library_Interface) are copied to the library directory. As a consequence, only the interface units may be imported from Ada units outside of the library. If other units are imported, the binding phase will fail.
Inlineare used, or when there is a generic units in the spec. This directory cannot point to the object directory or one of the source directories, but it can point to the library directory, which is the default value for this attribute.
"default": exported symbols are not controlled
"compliant": if attribute Library_Reference_Symbol_File is not defined, then it is equivalent to policy "autonomous". If there are exported symbols in the reference symbol file that are not in the object files of the interfaces, the major ID of the library is increased. If there are symbols in the object files of the interfaces that are not in the reference symbol file, these symbols are put at the end of the list in the newly created symbol file and the minor ID is increased.
"controlled": the attribute Library_Reference_Symbol_File must be defined. The library will fail to build if the exported symbols in the object files of the interfaces do not match exactly the symbol in the symbol file.
"restricted": The attribute Library_Symbol_File must be defined. The library will fail to build if there are symbols in the symbol file that are not in the exported symbols of the object files of the interfaces. Additional symbols in the object files are not added to the symbol file.
"direct": The attribute Library_Symbol_File must be defined and must designate an existing file in the object directory. This symbol file is passed directly to the underlying linker without any symbol processing.