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Switch settings for a project-aware tool can be specified through
attributes in the package that corresponds to the tool.
The example above illustrates one of the relevant attributes,
Default_Switches, which is defined in packages
in both project files.
Unlike simple attributes like Source_Dirs,
Default_Switches is
known as an associative array. When you define this attribute, you must
supply an “index” (a literal string), and the effect of the attribute
definition is to set the value of the array at the specified index.
For the Default_Switches attribute,
the index is a programming language (in our case, Ada),
and the value specified (after use) must be a list
of string expressions.
The attributes permitted in project files are restricted to a predefined set. Some may appear at project level, others in packages. For any attribute that is an associative array, the index must always be a literal string, but the restrictions on this string (e.g., a file name or a language name) depend on the individual attribute. Also depending on the attribute, its specified value will need to be either a string or a string list.
In the Debug project, we set the switches for two tools,
gnatmake and the compiler, and thus we include the two corresponding
packages; each package defines the Default_Switches
attribute with index "Ada".
Note that the package corresponding to
gnatmake is named Builder. The Release project is
similar, but only includes the Compiler package.
In project Debug above, the switches starting with
-gnat that are specified in package Compiler
could have been placed in package Builder, since gnatmake
transmits all such switches to the compiler.