Re: array_length(anyarray)
От | Marko Tiikkaja |
---|---|
Тема | Re: array_length(anyarray) |
Дата | |
Msg-id | 52B22C40.1070200@joh.to обсуждение исходный текст |
Ответ на | Re: array_length(anyarray) (David Johnston <polobo@yahoo.com>) |
Список | pgsql-hackers |
On 12/19/13, 12:01 AM, David Johnston wrote: > Marko Tiikkaja-4 wrote >> On 2013-12-18 22:32, Andrew Dunstan wrote: >>> You're not really free to assume it - you'll need an exception handler >>> for the other-than-1 case, or your code might blow up. >>> >>> This seems to be codifying a bad pattern, which should be using >>> array_lower() and array_upper() instead. >> >> That's the entire point -- I *want* my code to blow up. If someone >> passes a multi-dimensional array to a function that assumes its input is >> one-dimensional and its indexes start from 1, I want it to be obvious >> that the caller did something wrong. Now I either copy-paste lines and >> lines of codes to always test for the weird cases or my code breaks in >> subtle ways. >> >> This is no different from an Assert() somewhere -- if the caller breaks >> the documented interface, it's his problem, not mine. And I don't want >> to waste my time coding around the fact that this simple thing is so >> hard to do in PG. > > 1) Why cannot we just make the second argument of the current function > optional and default to 1? That still does the wrong thing for the empty array, multidimensional arrays and arrays that don't start from index 1. > 2) How about providing a function that returns the "1-dim/lower=1" input > array or raise/exception if the input array does not conform? > > <not tested/psuedo-code> > CREATE FUNCTION array_normal(arr anyarray) RETURNS anyarray > $$ > begin > if (empty(arr)) return arr; > if (ndim(arr) > 1) raise exception; > if (array_lower() <> 1) raise exception > return arr; > end; > $$ With this, I would still have to do COALESCE(array_length(array_normal($1), 1), 0). That's pretty stupid for the most common use case of arrays, don't you think? > I can also see wanting 1-dimensional enforced without having to require the > lower-bound to be 1 so maybe a separate function for that. I really don't see the point. How often have you ever created a function that doesn't have a lower bound of 1 on purpose? What good did it serve you? > Usage: > > SELECT array_length(array_normal(input_array)) > > I could see this being especially useful for a domain and/or column > constraint definition and also allowing for a textbook case of separation of > concerns. What would array_length() in this case be? With what you suggested above, you would still get NULL for an empty array. > I am torn, but mostly opposed, to making an array_length(anyarray) function > with these limitations enforced - especially if other similar functions are > not created at the same time. I fully agree that array_length(anyarray) > should be a valid call without requiring the user to specify ", 1" by rote. I'm specifically asking for something that is different from array_length(anyarray, int), because I personally think it's too full of caveats. Regards, Marko Tiikkaja
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