During development of a large system, it is sometimes necessary to use modified versions of some of the source files, without changing the original sources. This can be achieved through the project extension facility.
project Modified_Utilities extends "/baseline/utilities.gpr" is ...
A project extension declaration introduces an extending project (the child) and a project being extended (the parent).
By default, a child project inherits all the sources of its parent. However, inherited sources can be overridden: a unit in a parent is hidden by a unit of the same name in the child.
Inherited sources are considered to be sources (but not immediate sources) of the child project; see Project File Syntax.
An inherited source file retains any switches specified in the parent project.
For example if the project
Utilities contains the spec and the
body of an Ada package
Util_IO, then the project
Modified_Utilities can contain a new body for package
The original body of
Util_IO will not be considered in program builds.
However, the package spec will still be found in the project
A child project can have only one parent, except when it is qualified as abstract. But it may import any number of other projects.
A project is not allowed to import directly or indirectly at the same time a child project and any of its ancestors.