On 26 January 2013 10:58, Pavel Stehule <pavel.steh...@gmail.com> wrote: > updated patches due changes for better variadic "any" function. > > apply fix_mixing_positinal_ordered_placeholders_warnings_20130126.patch first >
Hi, No one is listed as a reviewer for this patch so I thought I would take a look at it, since it looks like a useful enhancement to format(). Starting with the first patch - it issues a new WARNING if the format string contains a mixture of format specifiers with and without parameter indexes (e.g., 'Hello %s, %1$s'). Having thought about it a bit, I really don't like this for a number of reasons: * I actually quite like the current behaviour. Admittedly putting ordered specifiers (like '%s') after positional ones (like '%3$s') is probably not so useful, and potentially open to different interpretations. But putting positional specifiers at the end is completely unambiguous and can save a lot of typing (e.g., '%s,%s,%s,%s,%,s,%s,%s,%1$s'). * On backwards compatibility grounds. The fact that the only example of format() in the manual is precisely a case of mixed positional and ordered parameters makes it quite likely that people will have used this feature already. * Part of the justification for adding the warning is for compatibility with glibc/SUS printf(). But if we are aiming for that, then we should also produce a warning if positional parameters are used and not all parameters are consumed. That would be a pain to implement and I don't think it would be particularly helpful in practice. Here is what the SUS says: """ The format can contain either numbered argument specifications (that is, %n$ and *m$), or unnumbered argument specifications (that is, % and *), but normally not both. The only exception to this is that %% can be mixed with the %n$ form. The results of mixing numbered and unnumbered argument specifications in a format string are undefined. When numbered argument specifications are used, specifying the Nth argument requires that all the leading arguments, from the first to the (N-1)th, are specified in the format string. """ I think that if we are going to do anything, we should explicitly document our current behaviour as a PostgreSQL extension to the SUS printf(), describing how we handle mixed parameters, rather than adding this warning. The current PostgreSQL code isn't inconsistent with the SUS, except in the error case, and so can reasonably be regarded as an extension. Regards, Dean -- Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org) To make changes to your subscription: http://www.postgresql.org/mailpref/pgsql-hackers
