Обсуждение: Add Optional Variadic Invocation Explanation to 35.4.5 (xfunc-sql)
CREATE FUNCTION varfunc (fixed1 text, VARIADIC vars text[]) [...]
SELECT varfunc('text fixed 1'); -- error: function signature not found; thus the number of supplied variadic values must be >= 1
Describes how to invoke a function defined with VARIADIC with an actual array as input instead of supplying ONE-or-more individual arguments to the call.
AFAICS the only way to get the called function to see an empty array is to call it like:
SELECT varchar('text fixed 1', VARIADIC ARRAY[]::text[])
While this is a logical solution to the problem, given the above knowledge, it would be nice if both points were made explicitly in the documentation in the section linked above.
Existing: "Sometimes it is useful to be able to pass an already-constructed array to a variadic function; this is particularly handy when one variadic function wants to pass on its array parameter to another one."
Change that to:
"Sometimes it is useful to be able to pass an already-constructed array to a variadic function."
<move existing sample to here>
"While this is particularly handy when one variadic function wants to pass on its array parameter to another[/cut] it is required if you wish to invoke the function without passing any optional arguments. The following example's first attempt to omit the variadic argument fails since the planner looks for a different function signature. By using the variadic invocation the second attempt succeeds. The alternative is to define an overloaded function without a VARIADIC parameter but with the same non-optional ones."
<better example maybe...but show/explain the two queries above>
Thoughts? Am I missing something?
David J.
David Johnston <david.g.johnston@gmail.com> writes: > This: > http://www.postgresql.org/docs/9.4/static/xfunc-sql.html > Describes how to invoke a function defined with VARIADIC with an actual > array as input instead of supplying ONE-or-more individual arguments to the > call. Right, and it does specifically say that there must be at least one actual argument matching the VARIADIC parameter. Still, an example to clarify that isn't a bad idea. > AFAICS the only way to get the called function to see an empty array is to > call it like: > SELECT varchar('text fixed 1', VARIADIC ARRAY[]::text[]) > While this is a logical solution to the problem, given the above knowledge, > it would be nice if both points were made explicitly in the documentation > in the section linked above. I did not like your proposed wording, as it seemed to complicate matters unduly by treating two independent points in the same para. I went with just adding a separate para instead: http://git.postgresql.org/gitweb/?p=postgresql.git;a=commitdiff;h=699300a146c04e207a8fdec407538cdf5368fde5 regards, tom lane