Re: RfD: more powerful "any" types

On Thu, 2009-09-10 at 22:15 +0200, Pavel Stehule wrote:
> 2009/9/10 Hannu Krosing <hannu(at)2ndquadrant(dot)com>:
> > On Thu, 2009-09-10 at 21:35 +0200, Pavel Stehule wrote:
> >> 2009/9/10 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
> >> > Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> >> >> I don't afraid about crashing. Simply I have not idea what sql
> >> >> sprintf's behave in case:
> >> >
> >> >> SELECT sprintf('some %s', 10)
> >> >
> >> > That one I don't think is hard --- coerce the input type to text and
> >> > print the string.
> >> >
> >> >> SELECT sprintf('some %d', 10::mycustomtype)
> >> >
> >> > For the formats that presume an integer or float input in C, perhaps
> >> > we could coerce to numeric (failing if that fails) and then print
> >> > appropriately. Or maybe int or float8 would be more appropriate
> >> > conversion targets.
> >>
> >> it's possible - so format tags doesn't mean data type, but it means
> >> "try to drow it as type" - etc invisible explicit casting.
> >
> >
> > what is the difference between these two ?
>
> first is coming from C and has C semantic - there is only one possible
> tag (without binary compatible types) - you cannot use %s for numbers,
> and %d for strings is some specific value.

Similar functionality in python allows %s for any type (it will just get
string representation of the value), but not vice-versa:

>>> '%s' % 10
'10'
>>> '%d' % 10
'10'
>>> '%d' % '10'
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: %d format: a number is required, not str

More restrictive than Tom's proposal.

> sprintf("%d", "10") - show address of static string "10"
>
> second is Tom's proposal. More dynamic. Tag specify target type.
>
> so sprintf('%d', '10') show 10 with possible width manipulation operations

this would be interesting for cases like

sprintf('%.2f', '3.1415927')

but I'd frefer here python-like sematics, where you need to make
explicit casts, i.e.

sprintf('%.2f', '3.1415927'::float)

--
Hannu Krosing http://www.2ndQuadrant.com
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