Re: Separate Compilation in Programming Languages

[Robert A Duff <bobduff@shell01.TheWorld.com>]

<adaworks@sbcglobal.net> writes:

> Recently, I have been engaged in some conversations with colleagues
> about the value of separate compilation.  This is one of my favorite
> features in Ada.  In fact, as nearly as I can tell, none of the other
> popular languages includes this feature in as well-developed a form as
> Ada.  Java has no separate compilation at all.  Nor does Eiffel.  C++
> has a rather kludgy form that is sometimes worse than none at all.
> Modula includes a form of separate compilation, but requires opaque
> types.  Older languages such as PL/I, COBOL, and Fortran are pretty
> useless in this respect.

Please define what you mean by "separate compilation".

My definition is that you can store parts of the program in separate
source files, and compile each source file separately from other source
files.  You can compile parts of incomplete programs.  In that sense,
all of the above-mentioned languages (or language implementations in
common use) have it.  So I'm puzzled by your statement to the contrary.

I've also heard the term "independent compilation" used for the above,
with "separate compilation" meaning that in addition, whatever type
checking is done within a single compilation unit should be done across
separately compiled units.  In that sense, Ada, Eiffel, Modula-2, and
Java still have separate compilation.  C and C++ do too, sort of, if you
rely on taking care with include files.  Still puzzled.

By the way, Eiffel compilers typically use incremental compilation,
which if implemented well, is strictly superior to separate
compilation on a file-by-file basis.

- Bob