Re: DBI package problem?

On Sun, 28 Mar 2010 23:40:35 +0200, [email protected] wrote:

> What is the preferred way of allowing a driver to use either
> DBI::PurePerl or DBI?

Because DBI::PurePerl is inside the DBI package, the only way to
disable DBI is to make your C compiler unavailable.

requiring DBI::PurePerl will, when not found, install DBI, which
includes DBI and DBI::PurePerl. The first will only not be installed
if it cannot be compiled.

> Module::Build does not support alternative requirements
> (one-or-the-other), but it does allow:
> =================================
>     requires => {
>         'DBI::PurePerl' => 0.0,
>         },
>     recommends => {
>         'DBI' => 0.0,
>         },
> =================================

Which will essentially require the same distribution.

It looks like you have no option but to require nothing, and try to
"require DBI::PurePerl" during Makefile.PL time maybe.

> In practice this results in circa 70% of smoke testers running the
> module with DBI installed.
> 
> The remaining 30% however, fails with this error:
> =================================
> #   Failed test 'use DBI;'
> #   at t/00-load.t line 4.
> #     Tried to use 'DBI'.
> #     Error:  Can't locate DBI.pm in @INC (@INC contains:
> [...snip...]) at (eval 4) line 2.
> # BEGIN failed--compilation aborted at (eval 4) line 2.
> =================================
> 
> I could easily change the "use DBI" line into a conditional "require
> DBI::PurePerl" during BEGIN, but this does not fix the root of the
> problem, namely that the PurePerl version of DBI never gets installed.

Why would someone install DBI::PurePerl with a working XS version?

> Being able to install DBI::PurePerl is unfortunately kind of critical
> to being able to use it in any way whatsoever..
> 
> Any good ideas?

Maybe too late now. But when Makamake took over Text::CSV, we discussed
the best interface. The old Text::CSV was heavily broken, and he wanted
Text::CSV to be the pur perl version of Text::CSV_XS.

We decided that the best plan was to create Text::CSV_PP to be the
pure-perl version of Text::CSV_XS and to Have Text::CSV choose the
fastest available on invocation. There is still a way to prefer either
by environment variables.

In order to do something similar with DBI, DBI should be renamed to
DBI::XS (or DBI_XS) and a new wrapper called DBI can at runtime select
either DBI::XS or DBI::PurePerl whatever is available. If this path
would be chosen, then it would be `normal' to also install
DBI::PurePerl because now the end-user has an option.

FWIW I am not the one going to implement this.

-- 
H.Merijn Brand  http://tux.nl      Perl Monger  http://amsterdam.pm.org/
using & porting perl 5.6.2, 5.8.x, 5.10.x, 5.11.x on HP-UX 10.20, 11.00,
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