Re: patch: to_string, to_array functions

On Wed, Jul 21, 2010 at 7:39 AM, Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> wrote:
> 2010/7/21 Robert Haas <robertmhaas(at)gmail(dot)com>:
>> On Wed, Jul 21, 2010 at 12:39 AM, Itagaki Takahiro
>> <itagaki(dot)takahiro(at)gmail(dot)com> wrote:
>>> 2010/7/20 Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com>:
>>>> here is a new version - new these functions are not a strict and
>>>> function to_string is marked as stable.
>>>
>>> We have array_to_string(anyarray, text) and string_to_array(text, text),
>>> and you'll introduce to_string(anyarray, text, text) and
>>> to_array(text, text, text).
>>> Do we think it is good idea to have different names for them?  IMHO, we'd
>>> better  use 3 arguments version of array_to_string() instead of the
>>> new to_string() ?
>>
>> The worst part is that the new names are not very mnemonic.
>>
>> I think maybe what we really need here is array equivalents of
>> COALESCE() and NULLIF().  It looks like the proposed to_string()
>> function is basically equivalent to replacing each NULL entry with the
>> array with a given value, and then doing array_to_string() as usual.
>> And it looks like the proposed to_array function basically does the
>> same thing as to_array(), and then replaces empty strings with NULL or
>> some other value.
>>
>> Maybe we just need a function array_replace(anyarray, anyelement,
>> anyelement) that replaces any element in the array that IS NOT
>> DISTINCT FROM $2 with $3 and returns the new array.  That could be
>> useful for other things besides this particular case, too.
>
> I don't agree. Building or updating any array is little bit expensive.
> There can be same performance issue like combination array_agg and
> array_to_string versus string_agg.

But is it really bad enough to introduce custom versions of every
function that might want to do this sort of thing?

> I am not against to possible name
> changes. But I am strong in opinion so current string_to_array and
> array_to_string are buggy and have to be deprecated.

But I don't think anyone else agrees with you. The current behavior
isn't the only one anyone might want, but it's one reasonable
behavior.

> p.s. can we use a names - text_to_array, array_to_text ?

That's not going to reduce confusion one bit...

--
Robert Haas
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