The previous section described the use of the Source_File_Name
pragma to allow arbitrary names to be assigned to individual source files.
However, this approach requires one pragma for each file, and especially in
large systems can result in very long
gnat.adc files, and also create
a maintenance problem.
GNAT also provides a facility for specifying systematic file naming schemes other than the standard default naming scheme previously described. An alternative scheme for naming is specified by the use of Source_File_Name pragmas having the following format:
pragma Source_File_Name ( Spec_File_Name => FILE_NAME_PATTERN [ , Casing => CASING_SPEC] [ , Dot_Replacement => STRING_LITERAL ] ); pragma Source_File_Name ( Body_File_Name => FILE_NAME_PATTERN [ , Casing => CASING_SPEC ] [ , Dot_Replacement => STRING_LITERAL ] ) ; pragma Source_File_Name ( Subunit_File_Name => FILE_NAME_PATTERN [ , Casing => CASING_SPEC ] [ , Dot_Replacement => STRING_LITERAL ] ) ; FILE_NAME_PATTERN ::= STRING_LITERAL CASING_SPEC ::= Lowercase | Uppercase | Mixedcase
The FILE_NAME_PATTERN string shows how the file name is constructed. It contains a single asterisk character, and the unit name is substituted systematically for this asterisk. The optional parameter Casing indicates whether the unit name is to be all upper-case letters, all lower-case letters, or mixed-case. If no Casing parameter is used, then the default is all lower-case.
The optional Dot_Replacement string is used to replace any periods that occur in subunit or child unit names. If no Dot_Replacement argument is used then separating dots appear unchanged in the resulting file name. Although the above syntax indicates that the Casing argument must appear before the Dot_Replacement argument, but it is also permissible to write these arguments in the opposite order.
As indicated, it is possible to specify different naming schemes for bodies, specs, and subunits. Quite often the rule for subunits is the same as the rule for bodies, in which case, there is no need to give a separate Subunit_File_Name rule, and in this case the Body_File_name rule is used for subunits as well.
The separate rule for subunits can also be used to implement the rather unusual case of a compilation environment (e.g., a single directory) which contains a subunit and a child unit with the same unit name. Although both units cannot appear in the same partition, the Ada Reference Manual allows (but does not require) the possibility of the two units coexisting in the same environment.
The file name translation works in the following steps:
As an example of the use of this mechanism, consider a commonly used scheme
in which file names are all lower case, with separating periods copied
unchanged to the resulting file name, and specs end with
bodies end with
.2.ada. GNAT will follow this scheme if the following
two pragmas appear:
pragma Source_File_Name (Spec_File_Name => ".1.ada"); pragma Source_File_Name (Body_File_Name => ".2.ada");
The default GNAT scheme is actually implemented by providing the following default pragmas internally:
pragma Source_File_Name (Spec_File_Name => ".ads", Dot_Replacement => "-"); pragma Source_File_Name (Body_File_Name => ".adb", Dot_Replacement => "-");
Our final example implements a scheme typically used with one of the
Ada 83 compilers, where the separator character for subunits was '__'
(two underscores), specs were identified by adding
.ADA, and subunits by
.SEP. All file names were
upper case. Child units were not present of course since this was an
Ada 83 compiler, but it seems reasonable to extend this scheme to use
the same double underscore separator for child units.
pragma Source_File_Name (Spec_File_Name => "_.ADA", Dot_Replacement => "__", Casing = Uppercase); pragma Source_File_Name (Body_File_Name => ".ADA", Dot_Replacement => "__", Casing = Uppercase); pragma Source_File_Name (Subunit_File_Name => ".SEP", Dot_Replacement => "__", Casing = Uppercase);