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<H1> 10.1 Separate Compilation</H1>
<DIV Class="Paranum"><FONT SIZE=-2>1</FONT></DIV>
<DIV Class="Normal"> [<A NAME="I3844"></A> <A NAME="I3845"></A><A NAME="I3846"></A>A
<I>program unit</I> is either a package, a task unit, a protected unit,
a protected entry, a generic unit, or an explicitly declared subprogram
other than an enumeration literal. Certain kinds of program units can
be separately compiled. Alternatively, they can appear physically nested
within other program units.</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3847"></A>The text of a program can
be submitted to the compiler in one or more <FONT FACE="Arial, Helvetica">compilation</FONT>s.
Each <FONT FACE="Arial, Helvetica">compilation</FONT> is a succession
of <FONT FACE="Arial, Helvetica">compilation_unit</FONT>s. A <FONT FACE="Arial, Helvetica">compilation_unit</FONT>
contains either the declaration, the body, or a renaming of a program
unit.] The representation for a <FONT FACE="Arial, Helvetica">compilation</FONT>
is implementation-defined. </DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Implementation defined: </B>The
representation for a <FONT FACE="Arial, Helvetica">compilation</FONT>.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Ramification: </B>Some implementations
might choose to make a <FONT FACE="Arial, Helvetica">compilation</FONT>
be a source (text) file. Others might allow multiple source files to
be automatically concatenated to form a single <FONT FACE="Arial, Helvetica">compilation</FONT>.
Others still may represent the source in a nontextual form such as a
parse tree. Note that the RM95 does not even define the concept of a
source file.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2.c</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>Note that a protected subprogram
is a subprogram, and therefore a program unit. An instance of a generic
unit is a program unit.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>2.d</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>A protected entry is a program
unit, but protected entries cannot be separately compiled. </FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>3</FONT></DIV>
<DIV Class="Normal"> <A NAME="I3848"></A>A library unit is a separately
compiled program unit, and is always a package, subprogram, or generic
unit. Library units may have other (logically nested) library units as
children, and may have other program units physically nested within them.
<A NAME="I3849"></A>A root library unit, together with its children and
grandchildren and so on, form a <I>subsystem</I>.</DIV>
<H4 ALIGN=CENTER>Implementation Permissions</H4>
<DIV Class="Paranum"><FONT SIZE=-2>4</FONT></DIV>
<DIV Class="Normal"> An implementation may impose implementation-defined
restrictions on <FONT FACE="Arial, Helvetica">compilation</FONT>s that
contain multiple <FONT FACE="Arial, Helvetica">compilation_unit</FONT>s.
</DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4.a</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Implementation defined: </B>Any
restrictions on <FONT FACE="Arial, Helvetica">compilations</FONT> that
contain multiple <FONT FACE="Arial, Helvetica">compilation_unit</FONT>s.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4.b</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1><B>Discussion: </B>For example,
an implementation might disallow a <FONT FACE="Arial, Helvetica">compilation</FONT>
that contains two versions of the same compilation unit, or that contains
the declarations for library packages P1 and P2, where P1 precedes P2
in the <FONT FACE="Arial, Helvetica">compilation</FONT> but P1 has a
<FONT FACE="Arial, Helvetica">with_clause</FONT> that mentions P2. </FONT></DIV>
<H4 ALIGN=CENTER>Wording Changes from Ada 83</H4>
<DIV Class="Paranum"><FONT SIZE=-2>4.c</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>The interactions between language
issues and environmental issues are left open in Ada 95. The environment
concept is new. In Ada 83, the concept of the program library, for example,
appeared to be quite concrete, although the rules had no force, since
implementations could get around them simply by defining various mappings
from the concept of an Ada program library to whatever data structures
were actually stored in support of separate compilation. Indeed, implementations
were encouraged to do so.</FONT></DIV>
<DIV Class="Paranum"><FONT SIZE=-2>4.d</FONT></DIV>
<DIV Class="Annotations"><FONT SIZE=-1>In RM83, it was unclear which
was the official definition of ``program unit.'' Definitions appeared
in RM83-5, 6, 7, and 9, but not 12. Placing it here seems logical, since
a program unit is sort of a potential compilation unit. </FONT></DIV>
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