🚀 go-pugleaf

dechc00@tohi.DMI.USherb.Ca (CHRISTIAN DECHAMPLAIN) writes:

>I understand the reasons why nobody wants to change the linkers, then how
>about a pre-linker!

That's what I was thinking.  The C++ compiler already uses stabs (or
whatever) to map object code back to the original source files; it
should be possible to use the same features for generating templates.
Have the compiler generate stabs information that points template
symbols back to the original header files.  Just before the usual
linking, a pre-linker sweeps through all the object files and looks
for unresolved template symbols (the mangler should make template
symbols obvious).  The pre-linker does consistency checks, then
compiles the template source files for every needed case, without
duplication.  After it's done, it strips the stabs info out of the
original object files and calls the "regular" linker.  To save time,
there might be an option to save the automatically generated ".o"
files in the compilation directory.

There are a couple of simple ways of finding the definitions/source
code with this method.

 * the library writer could just stick them into the header file (which
would probably be compatible with the current G++ method---oh boy).
The compiler would keep track of template definitions that it saw, but
otherwise would just ignore them until pre-link time (at which point
the header file would be interpreted as a regular source file).

 * the compiler could assume that if the header file was
"/usr/include/foo.hh", then the corresponding source file would be
named "/usr/include/foo.cc" (Dialect Alert!), stored in the same
directory; the pre-linker would just look through the same set of
#include directories as the pre-processor (which does mean the current
directory as well).

 * To be really sure, the library writer could add a #pragma directive
of some sort to the header file.  This would also be helpful as a
supplement to the other two.

The first method has a slight edge in that it's a bit more
idiot-proof.  It should also deal more gracefully with the case of a
template function (as opposed to a template class with template
members) that is defined and used throughout a single ".cc" file.

Derek

-- 
Derek Lynn Upham                               University of British Columbia
upham@cs.ubc.ca                                   Computer Science Department
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