Re: Mostly Harmless: Welcoming our C++ friends

Added to TODO:

Allow C++ code to more easily access backend code

* http://archives.postgresql.org/pgsql-hackers/2008-12/msg00302.php

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Kurt Harriman wrote:
> > Is there anything in the source that would necessarily preclude using the
> > C++ compiler to build *all* the code?
>
> No. Most of the source files would need a sprinkling of
> tiny changes: typically only a handful of casts need to be
> added. Some files would need more widespread (but still
> trivial) changes, such as renaming local variables or
> parameters which are C++ reserved words. There are a few
> head-scratchers: see this post (1 July 2007)
> http://groups.google.com/group/pgsql.patches/msg/91775dc1355cdc72
> or http://tinyurl.com/6a67ms
>
> I've actually gone through the tedious experiment of fixing up
> about 40 of the source files so they can be compiled as either
> C or C++. With these files compiled as C++, and the remainder
> compiled as C, PostgreSQL builds successfully and passes the
> 'make check' regression tests. The intermixture of C together
> with C-compiled-as-C++ works just fine, at least on my x86-32
> Linux platform. On the other hand, PostgreSQL already works
> as C; trying to convert it all to C++ doesn't seem useful.
>
> Suppose we were to use the C++ compiler to build all of
> PostgreSQL. Consider the alternatives: either
>
> A) switch over entirely to C++, no longer supporting C; or
>
> B) let the build farm do a nightly build with a C++ compiler
> merely as a test to verify that no C++ compilation errors
> are introduced, but continue to use C 'officially' for
> builds and releases; or
>
> C) support C and C++ equally, allowing the choice to be made
> by each person who builds PostgreSQL from source.
>
> Alternative A breaks (almost?) all existing third party
> extension code: sufficient reason to rule out this alternative.
>
> With Alternative B, most development work would probably still
> be done in C. C programmers surely won't embrace the idea
> that they should conform to C++ rules and take care that their
> C code is C++-compilable. Some of the C++ rules are obscure;
> rare is the C++ programmer who never omits a needed cast.
> Every patch will have to be checked for C++ compatibility.
> If the build farm detects a C++ error, likely one of the
> committers would be saddled with the burden of backing
> out the patch and/or correcting the error.
>
> Alternative C seems to just about double the amount of work
> involved in every commit, build, and release. Again, much
> of the burden probably falls on the committers.
>
> All the extra work and trouble will be justified if there is
> a truly spectacular payoff. What magnificence awaits us when
> all of PostgreSQL is C++-compilable? I don't have a good
> answer.
>
> The best alternative, in my opinion, is "none of the above".
> That's why I have instead offered some patches to enable C++
> for new extensions and add-on development with minimal
> impact to the C core.
>
> As a courteous host, one might extend hospitality to a guest,
> but not indeed go so far as to redecorate the house from top
> to bottom to suit the guest's taste.
>
> Regards,
> ... kurt
>
> James Mansion wrote:
> > Is there anything in the source that would necessarily preclude using the
> > C++ compiler to build *all* the code?
> >
> > I'd guess that this would be quite a big patch to do this in any places
> > where we have implicit conversions from void* to char* etc, but
> > the result is valid as C and C++ and arguably better documented.
> >
> > C++ is picky about a few things you can do in C, but most of them
> > are things I'd rather not do anyway.
> >
> > Run such a build on the build farm each night, and it will be obvious as
> > soon as C++-unfriendly code sneaks in.
> >
> > And who know, maybe eventually we could use C++ properly in the
> > code.
> >
> > James
>
>
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Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
EnterpriseDB http://enterprisedb.com

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