🚀 go-pugleaf

Recently, Paul Chisholm replied to Dominich Samperi's query on this
subject, saying that this idea had been beaten to death recently.
He went on to summarize the discussion, saying roughly that the two
extreme solutions to "the include file problem" are

1) Write "foo.h" in the form
#ifndef _FOO_H_
#define _FOO_H_ 1
<contents of foo.h>
#endif // _FOO_H_

This requires no modifications to cpp.

2) Build a cpp so that it never includes a file twice -- this
increases efficeincy significantly because, unlike the above, it
doesn't even have to open the file to determine that it doesn't need
to be included.  Unfortunately, despite what many of us might think
about such usage, some files are written to be included multiple
times.

Many people in the discussion tried to find compromise solutions; I
was one of them.  Unfortunately, my idea didn't work.  I'm posting to
plug what I thought was the best solution I read; I think all cpp's
should be written this way (I forget who proposed this -- they should
take a bow, I think):

When cpp first processes a file, it determines all non-comment,
non-whitespace text in the file is enclosed in an #ifndef block, as
above.  If so, the file name and the variable whose definedness
determines inclusion are put in a table.  On subsequent includes, the
file is opened and processed only if the variable is not defined.
This would seem to have all the performance advantages of proposal 2,
while retaining all the compatibility advantages of proposal 1.  Just
a marvelous idea.


--
Dave Detlefs			Any correlation between my employer's opinion
Carnegie-Mellon CS		and my own is statistical rather than causal,
dld@cs.cmu.edu			except in those cases where I have helped to
				form my employer's opinion.  (Null disclaimer.)
--